Normal Lab Values: Definition + What High/Low Values Mean

  1. Laboratory Values
  2. Electrolytes
  3. Hematology
  4. Lipids
  5. Acid Base Values
  6. Gastrointestinal Tests
  7. Cardiac Enzymes
  8. Hormones
  9. Vitamins
  10. Tumor Markers
  11. Miscellaneous
  12. Comparing the Client's Laboratory Values to Normal Laboratory Values
  13. Educating the Client About the Purpose and Procedure of Prescribed Laboratory Tests
  14. Peripheral Venous Blood Samples
  15. Central Line Blood Samples
  16. Obtaining Specimens Other Than Blood for Diagnostic Testing
  17. Monitoring the Client's Laboratory Values
  18. Notifying the Primary Health Care Provider About Laboratory Test Results
  19. Normal Lab Values – Common Laboratory Values
  20. What are normal lab values?
  21. HEMATOLOGY – White Blood Cells. Back to top
  22. HEMOGLOBIN Back to top
  23. HEMATOCRIT Back to top
  24. CARDIAC MARKERS Back to top
  25. GENERAL CHEMISTRY Back to top
  26. URINE Back to top
  27. COAGULATION Back to top
  31. ARTERIAL VALUES Back to top
  32. VENOUS VALUES Back to top
  33. Normal Lab Values: Definition + What High/Low Values Mean
  34. What Are Normal Lab Values?
  35. How Reference Ranges Are Created
  36. Reference Interval Studies
  37. A Posteriori Studies
  38. Decision Limits
  39. Why Labs Have Different Reference Ranges
  40. Pros of Reference Ranges
  41. Cons of Reference Ranges
  42. What Does it Mean if My Lab Value is Outside the Normal Range?
  43. Normal Lab Values vs. Optimal Values
  44. Limitations
  45. Hematocrit Blood Test: Normal, High, Low Ranges & Results
  46. How Is the Hematocrit Measured?
  47. What Is a Normal Hematocrit?
  48. What Does a Low Hematocrit Mean?
  49. What Does a High Hematocrit Mean?
  50. How Is a Low or High Hematocrit Treated?
  51. Reference Ranges and What They Mean

Laboratory Values

Normal Lab Values: Definition + What High/Low Values Mean

In this section of the NCLEX-RN examination, you will be expected to demonstrate your knowledge and skills of laboratory values in order to:

  • Identify laboratory values for ABGs (pH, PO2, PCO2, SaO2, HCO3), BUN, cholesterol (total) glucose, hematocrit, hemoglobin, glycosylated hemoglobin (HgbA1C), platelets, potassium, sodium, WBC, creatinine, PT, PTT & APTT, INR
  • Compare client laboratory values to normal laboratory values
  • Educate client about the purpose and procedure of prescribed laboratory tests
  • Obtain blood specimens peripherally or through central line
  • Obtain specimens other than blood for diagnostic testing (e.g., wound, stool, urine)
  • Monitor client laboratory values (e.g., glucose testing results for the client with diabetes)
  • Notify primary health care provider about laboratory test results
  • Partial pressure of oxygen (PaO2): 75 – 100 mmHg
  • Partial pressure of carbon dioxide (PaCO2): 38 – 42 mmHg
  • Arterial blood pH: 7.38 – 7.42
  • Oxygen saturation (SaO2): 94 – 100%
  • Bicarbonate – (HCO3): 22 – 28 mEq/L

The oxygen value is lower with an altitude of > 3,000 feet.


  • Ammonia: 15-50 µmol/L
  • Ceruloplasmin: 15-60 mg/dL
  • Chloride: 95-105 mmol/L
  • Copper: 70-150 µg/dL
  • Creatinine: 0.8-1.3 mg/dL
  • Blood urea nitrogen: 8-21 mg/dL
  • Ferritin: 12-300 ng/mL (men), 12-150 ng/mL (women)
  • Glucose: 65-110 mg/dL
  • Inorganic phosphorous: 1-1.5 mmol/L
  • Ionized calcium: 1.03-1.23 mmol/L
  • Magnesium: 1.5-2 mEq/L
  • Phosphate: 0.8-1.5 mmol/L
  • Potassium: 3.5-5 mmol/L
  • Pyruvate: 300-900 µg/dL
  • Sodium: 135-145 mmol/L
  • Total calcium: 2-2.6 mmol/L
  • Total iron-binding capacity: 45-85 µmol/L
  • Total serum iron: 65-180 µg/dL (men), 30-170 µg/dL (women)
  • Transferrin: 200-350 mg/dL
  • Urea: 1.2-3 mmol/L
  • Uric acid: 0.18-0.48 mmol/L
  • Zinc: 70-100 µmol/L


  • Hemoglobin: 13-17 g/dL (men), 12-15 g/dL (women)
  • Hematocrit 40%-52% (men), 36%-47%
  • Glycosylated hemoglobin 4%-6%
  • Mean corpuscular volume (MCV): 80-100 fL
  • Red blood cell distribution width (RDW): 11.5%-14.5%
  • Mean corpuscular hemoglobin (MCH): 0.4-0.5 fmol/cell
  • Mean corpuscular hemoglobin concentration (MCHC): 30-35 g/dL
  • Reticulocytes 0.5%-1.5%
  • White blood cells (WBC) 4-10 x 109/L
  • Neutrophils: 2-8 x 109/L
  • Bands: < 1 x 109/L
  • Lymphocytes: 1-4 x 109/L
  • Monocytes: 0.2-0.8 x 109/L
  • Eosinophils: < 0.5 x 109/L
  • Platelets: 150-400 x 109/L
  • Prothrombin time: 11-14 sec
  • International normalized ratio (INR): 0.9-1.2
  • Activated partial thromboplastin time (aPTT): 20-40 sec
  • Fibrinogen: 1.8-4 g/L
  • Bleeding time: 2-9 min


  • Triglycerides: 50-150 mg/dL
  • Total cholesterol: 3-5.5 mmol/L
  • High-density lipoprotein (HDL): 40-80 mg/dL
  • Low-density lipoprotein (LDL): 85-125 mg/dL

Acid Base Values

  • pH: 7.35-7.45
  • Base excess: (-3)-(+3)
  • H+: 36-44 nmol/L
  • Partial pressure of oxygen (pO2): 75-100 mm Hg
  • Oxygen saturation: 96%-100%
  • Partial pressure of carbon dioxide (pCO2): 35-45 mm Hg
  • Bicarbonate (HCO3): 18-22 mmol/L

Gastrointestinal Tests

  • Albumin: 35-50 g/L
  • Alkaline phosphatase: 50-100 U/L
  • Alanine aminotransferase (ALT): 5-30 U/L
  • Amylase: 30-125 U/L
  • Aspartate aminotransferase (AST): 5-30 U/L
  • Direct bilirubin: 0-6 µmol/L
  • Gamma glutamyl transferase: 6-50 U/L
  • Lipase: 10-150 U/L
  • Total bilirubin: 2-20 µmol/L
  • Total protein: 60-80 g/L

Cardiac Enzymes

  • Creatine kinase: 25-200 U/L
  • Creatine kinase MB (CKMB): 0-4 ng/mL
  • Troponin: 0-0.4 ng/mL


  • 17 hydroxyprogesterone (female, follicular): 0.2-1 mg/L
  • Adrenocorticotropic hormone (ACTH): 4.5-20 pmol/L
  • Estradiol: 1.5-5 ng/dL (male), 2-14 ng/dL (female, follicular), 2-16 ng/dL (female, luteal), < 3.5 ng/dL (postmenopausal)
  • Free T3: 0.2-0.5 ng/dL
  • Free T4: 10-20 pmol/L
  • Follicle-stimulating hormone (FSH): 1-10 IU/L (male), 1-10 IU/L (female, follicular/luteal), 5-25 IU/L (female, ovulation), 30-110 IU/L (postmenopause)
  • Growth hormone (fasting) : 0-5 ng/mL
  • Progesterone: 70-280 (ovulation), ng/dL
  • Prolactin: < 14 ng/mL
  • Testosterone (male): 10-25 nmol/L
  • Thyroxine-binding globulin: 12-30 mg/L
  • Thyroid-stimulating hormone (TSH): 0.5-5 mIU/L
  • Total T4: 4.9-11.7 mg/dL
  • Total T3: 0.7-1.5 ng/dL
  • Free T3: 0.6-1.6 ng/mL


  • Folate (serum) : 7-36 nmol/L
  • Vitamin A: 30-65 µg/dL
  • Vitamin B12: 130-700 ng/L
  • Vitamin C: 0.4-1.5 mg/dL
  • Vitamin D: 5-75 ng/mL

Tumor Markers

  • Alpha fetoprotein: 0-44 ng/mL
  • Beta human chorionic gonadotropin (HCG): < 5 IU/I
  • CA19.9: < 40 U/mL
  • Carcinoembryonic antigen (CEA): < 4 ug/L
  • Prostatic acid phosphatase (PAP): 0-3 U/dL
  • Prostate-specific antigen (PSA): < 4 ug/L


  • Alpha 1-antitrypsin: 20-50 µmol/L
  • Angiotensin-converting enzyme: 23-57 U/L
  • C-reactive protein: < 5 mg/L
  • D-dimer: < 500 ng/mL
  • Erythrocyte sedimentation rate (ESR): Less than age/2 mm/hour
  • Lactate dehydrogenase (LDH): 50-150 U/L
  • Lead: < 40 µg/dL
  • Rheumatoid factor: < 25 IU/ml

Comparing the Client's Laboratory Values to Normal Laboratory Values

The client's current laboratory values are compared to the normal laboratory values, as above, in order to determine the physiological status of the client and to compare the current values during treatment to the laboratory values taken prior to a treatment.

Educating the Client About the Purpose and Procedure of Prescribed Laboratory Tests

As previously discussed, clients must be educated about the purpose of the prescribed laboratory test, the procedure for the laboratory test and any preparation the laboratory tests that is indicated.

For example, a client in the community may be instructed to remain NPO after midnight.

More information about this client education was previously discussed in the section entitled “Applying a Knowledge of Related Nursing Procedures and Psychomotor Skills When Caring for Clients Undergoing Diagnostic Testing”.

Peripheral Venous Blood Samples

Drawing a peripheral venous blood sample is done in this manner:

  • Gather and organize the correct laboratory tubes for the specimens that you will be collecting.
  • Choose a suitable site for the venipuncture.
  • Place the tourniquet on the client's arm about 3 to 4 inches above the selected site.
  • Palpate the vein.
  • Clean the site with an alcohol prep pad with a circular pattern from the site of the venipuncture to the area surrounding the site of the venipuncture.
  • Allow the area to air dry.
  • Ask the patient to make a fist.
  • Pull the skin taunt so that the desired and suitable vein is accessible.
  • Insert the sterile needle into the vein at a 15 to 30 degree angle.
  • Pop the tube onto the tubing.
  • Take the tourniquet off when the last tube is filled.
  • Take the needle out.
  • Place sterile gauze on the site using sufficient pressure to prevent bleeding for about 1 or 2 minutes.
  • Remove the gauze.
  • Place an adhesive bandage over the site.
  • Label the specimen with the data that is required according to your facility's policy and procedure for laboratory blood samples.

Central Line Blood Samples

Some central venous catheters have a couple or several lumens, one of may be used to withdraw a blood sample. The port that can be used to draw a blood sample is cleansed with alcohol. Then a small amount of blood is drawn out and discarded, after which the intended blood sample is drawn. After the sample is taken, the central line is then flushed with 20 mL of sterile saline.

Obtaining Specimens Other Than Blood for Diagnostic Testing

Other than blood, other specimens that are collected include urine, stool and wound specimens. Urine and stool specimens were discussed earlier in this NCLEX-RN review in the section entitled “Applying a Knowledge of Related Nursing Procedures and Psychomotor Skills When Caring for Clients Undergoing Diagnostic Testing”

Wound specimens are obtained in the following manner:

  • Gently irrigate the wound with sterile normal saline to remove any debris and extraneous matter.
  • Remove the swab from the Culturette tube.
  • Gently place the swab and rotate the swab on the wound's granulating tissue.
  • Place the swab into the Culturette tube.
  • Crack the Culturette tube so the culture medium soaks into the swab

Monitoring the Client's Laboratory Values

Client's laboratory values are monitored prior to, during and after therapeutic interventions and treatments.

For example, diabetic clients should have their blood glucose levels are taken and monitored by the nurse and they are also monitored by the client in their home.

This monitoring permits the nurse and the client the opportunity to evaluate how well the diabetes is being managed.

Notifying the Primary Health Care Provider About Laboratory Test Results

The primary health care provider is immediately informed about all abnormal laboratory test results.


SEE – Reduction of Risk Potential Practice Test Questions

Alene Burke RN, MSN is a nationally recognized nursing educator. She began her work career as an elementary school teacher in New York City and later attended Queensborough Community College for her associate degree in nursing.

She worked as a registered nurse in the critical care area of a local community hospital and, at this time, she was committed to become a nursing educator.

She got her bachelor’s of science in nursing with Excelsior College, a part of the New York State University and immediately upon graduation she began graduate school at Adelphi University on Long Island, New York.

She graduated Summa Cum Laude from Adelphi with a double masters degree in both Nursing Education and Nursing Administration and immediately began the PhD in nursing coursework at the same university.

She has authored hundreds of courses for healthcare professionals including nurses, she serves as a nurse consultant for healthcare facilities and private corporations, she is also an approved provider of continuing education for nurses and other disciplines and has also served as a member of the American Nurses Association’s task force on competency and education for the nursing team members.


Normal Lab Values – Common Laboratory Values

Normal Lab Values: Definition + What High/Low Values Mean

Laboratory tests are procedures wherein a sample of blood, urine, other bodily fluid or tissue are checked in order to know more about a person’s health. The results of the test will show if a person is within the normal lab values.

What are normal lab values?

According to the Food and Drug Administration (FDA), normal lab test values are a set of upper and lower limits generally given as a range since normal values vary from person to person.

Laboratory tests are commonly administered in discovering the cause of symptoms, confirming a diagnosis and screening for diseases.

The information obtained from the test can also help rule out, asses and monitor the progression of a disease and plan for treatment.

All laboratory test results should be interpreted within the context of the patient’s general health and must be used with additional exams or tests.

A doctor will send the sample collected to a laboratory for testing. The sample will be tested to see how it reacts to different substances. The results will then be returned to the doctor to determine health conditions. Laboratories may also compare previous tests to see if there is a change in condition.

There are many factors that can affect lab results including sex, age, race, medical history and general health. Food, drugs, laboratory techniques and changes in laboratories may also affect results. In most cases, patients are advised to defer from drinking, eating and taking medication several hours before the tests.

The FDA is the regulating body in charge of the development and marketing of laboratory tests that use test kits and equipment commercially manufactured in the United States. Once approved, federal and state agencies ensure that test materials and equipment meet manufacturing and use standards.

The following lab values is just a partial listing of the information provided to students enrolled in select training courses. Click on the specific term to see their normal lab values:

It is the measurement of the normal range of red blood cell count of a person.

  • RBC (Male) 4.2 – 5.6 106 / µL [Scientific Notation: 106 = 1,000,000]
  • RBC (Female) 3.8 – 5.1 106 / µL
  • RBC (Child) 3.5 – 5.0 106 / µL

HEMATOLOGY – White Blood Cells. Back to top

It is the measurement of the white blood cell count in the body.

  • WBC (Male) 3.8 – 11.0 103 / mm3 [Scientific Notation: 103 = 1,000]
  • WBC (Female) 3.8 – 11.0 103 / mm3
  • WBC (Child) 5.0 – 10.0 103 / mm3

HEMOGLOBIN Back to top

Diseases that affect red blood cells or the amount of hemoglobin in the blood may be

  • Hgb (Male) 14 – 18 g/dL
  • Hgb (Female) 11 – 16 g/dL
  • Hgb (Child) 10 – 14 g/dL
  • Hgb (Newborn) 15 – 25 g/dL

HEMATOCRIT Back to top

Determines the proportion of blood that is made up of red blood cells and may be used to determine the severity of anemia.

  • Hct (Male) 39 – 54%
  • Hct (Female) 34 – 47%
  • Hct (Child) 30 – 42%
  • MCV 78 – 98 fL
  • MCH 27 – 35 pg
  • MCHC 31 – 37%
  • neutrophils 50 – 81%
  • bands 1 – 5%
  • lymphocytes 14 – 44%
  • monocytes 2 – 6%
  • eosinophils 1 – 5%
  • basophils 0 – 1%


Used to diagnose patients with chest discomfort suspected with acute coronary syndrome (ACS).

  • troponin I 0 – 0.1 ng/ml (onset: 4-6 hrs, peak: 12-24 hrs, return to normal: 4-7 days)
  • troponin T 0 – 0.2 ng/ml (onset: 3-4 hrs, peak: 10-24 hrs, return to normal: 10-14 days)
  • myoglobin (Male) 10 – 95 ng/ml (onset: 1-3 hrs, peak: 6-10 hrs, return to normal: 12-24 hrs)
  • myoglobin (Female) 10 – 65 ng/ml (onset: 1-3 hrs, peak: 6-10 hrs, return to normal: 12-24 hrs)


The general chemistry panel evaluates a number of the body’s components.

  • acetone 0.3 – 2.0 mg%
  • albumin 3.5 – 5.0 gm/dL
  • alkaline phosphatase 32 – 110 U/L
  • anion gap 5 – 16 mEq/L
  • ammonia 11 – 35 µmol/L
  • amylase 50 – 150 U/dL
  • AST,SGOT (Male) 7 – 21 U/L
  • AST,SGOT (Female) 6 – 18 U/L
  • bilirubin, direct 0.0 – 0.4 mg/dL
  • bilirubin, indirect total minus direct
  • bilirubin, total 0.2 – 1.4 mg/dL
  • BUN 6 – 23 mg/dL
  • calcium (total) 8 – 11 mg/dL
  • carbon dioxide 21 – 34 mEq/L
  • carbon monoxide symptoms at greater than or equal to 10% saturation
  • chloride 96 – 112 mEq/L
  • creatine (Male) 0.2 – 0.6 mg/dL
  • creatine (Female) 0.6 – 1.0 mg/dL
  • creatinine 0.6 – 1.5 mg/dL
  • ethanol 0 mg%; Coma:
  • greater than or equal to 400 – 500 mg%
  • folic acid 2.0 – 21 ng/mL
  • glucose 65 – 99 mg/dL
  • (diuresis greater than or equal to 180 mg/dL)
  • HDL (Male) 25 – 65 mg/dL
  • HDL (Female) 38 – 94 mg/dL
  • iron 52 – 169 µg/dL
  • iron binding capacity 246 – 455 µg/dL
  • lactic acid 0.4 – 2.3 mEq/L
  • lactate 0.3 – 2.3 mEq/L
  • lipase 10 – 140 U/L
  • magnesium 1.5 – 2.5 mg/dL
  • osmolarity 276 – 295 mOsm/kg
  • parathyroid hormone 12 – 68 pg/mL
  • phosphorus 2.2 – 4.8 mg/dL
  • potassium 3.5 – 5.5 mEq/L
  • SGPT 8 – 32 U/L
  • sodium 135 – 148 mEq/L
  • T3 0.8 – 1.1 µg/dL
  • thyroglobulin less than 55 ng/mL
  • thyroxine (T4) (total) 5 – 13 µg/dL
  • total protein 5 – 9 gm/dL
  • TSH Less than 9 µU/mL
  • urea nitrogen 8 – 25 mg/dL
  • uric acid (Male) 3.5 – 7.7 mg/dL
  • uric acid (Female) 2.5 – 6.6 mg/dL
  • LIPID PANEL (Adult)
  • cholesterol (total) Less than 200 mg/dL desirable
  • cholesterol (HDL) 30 – 75 mg/dL
  • cholesterol (LDL) Less than 130 mg/dL desirable
  • triglycerides (Male) Greater than 40 – 170 mg/dL
  • triglycerides (Female) Greater than 35 – 135 mg/dL

URINE Back to top

Urine tests are used to diagnose different metabolic and kidney disorders.

  • color Straw
  • specific gravity 1.003 – 1.040
  • pH 4.6 – 8.0
  • Na 10 – 40 mEq/L
  • K Less than 8 mEq/L
  • C1 Less than 8 mEq/L
  • protein 1 – 15 mg/dL
  • osmolality 80 – 1300 mOsm/L
  • amylase 250 – 1100 IU / 24 hr
  • calcium 100 – 250 mg / 24 hr
  • chloride 110 – 250 mEq / 24 hr
  • creatinine 1 – 2 g / 24 hr
  • creatine clearance (Male) 100 – 140 mL / min
  • creatine clearance (Male) 16 – 26 mg / kg / 24 hr
  • creatine clearance (Female) 80 – 130 mL / min
  • creatine clearance (Female) 10 – 20 mg / kg / 24 hr
  • magnesium 6 – 9 mEq / 24 hr
  • osmolality 450 – 900 mOsm / kg
  • phosphorus 0.9 – 1.3 g / 24 hr
  • potassium 35 – 85 mEq / 24 hr
  • protein 0 – 150 mg / 24 hr
  • sodium 30 – 280 mEq / 24 hr
  • urea nitrogen 10 – 22 gm / 24 hr
  • uric acid 240 – 755 mg / 24 hr


Coagulation factor tests calculate the role of proteins necessary for blood clot formation.

  • ACT 90 – 130 seconds
  • APTT 21 – 35 seconds
  • platelets 140,000 – 450,000 /ml
  • plasminogen 62 – 130%
  • PT 10 – 14 seconds
  • PTT 32 – 45 seconds
  • FSP Less than 10 µg/dL
  • fibrinogen 160 – 450 mg/dL
  • bleeding time 3 – 7 minutes
  • thrombin time 11 – 15 seconds


It is a series of tests that assess substances present in the cerebral spinal fluid in order to be able to diagnose circumstances affecting the central nervous system.

  • appearance clear
  • glucose 40 – 85 mg/dL
  • osmolality 290 – 298 mOsm/L
  • pressure 70 – 180 mm/H2O
  • protein 15 – 45 mg/dL
  • total cell count 0 – 5 cells
  • WBCs 0 – 6 / µL


The examination of hemodynamic parameters over time, such as blood pressure and heart rate in order to gauge blood flow and circulation.

  • cardiac index 2.5 – 4.2 L / min / m2
  • cardiac output 4 – 8 LPM
  • left ventricular stroke work index 40 – 70 g / m2 / beat
  • right ventricular stroke work index 7 – 12 g / m2 / beat
  • mean arterial pressure 70 – 105 mm Hg
  • pulmonary vascular resistance 155 – 255 dynes / sec / cm to the negative 5
  • pulmonary vascular resistance index 255 – 285 dynes / sec / cm to the negative 5
  • stroke volume 60 – 100 mL / beat
  • stroke volume index 40 – 85 mL / m2 / beat
  • systemic vascular resistance 900 – 1600 dynes / sec / cm to the negative 5
  • systemic vascular resistance index 1970 – 2390 dynes / sec / cm to the negative 5
  • systolic arterial pressure 90 – 140 mm Hg
  • diastolic arterial pressure 60 – 90 mm Hg
  • central venous pressure 2 – 6 mm Hg; 2.5 – 12 cm H2O
  • ejection fraction 60 – 75%
  • left arterial pressure 4 – 12 mm Hg
  • right atrial pressure 4 – 6 mm Hg
  • pulmonary artery systolic 15 – 30 mm Hg
  • pulmonary artery diastolic 5 – 15 mm Hg
  • pulmonary artery pressure 10 – 20 mm Hg
  • pulmonary artery wedge pressure 4 – 12 mm Hg
  • pulmonary artery end diastolic pressure 8 – 10 mm Hg
  • right ventricular end diastolic pressure 0 – 8 mm Hg


Confirms or excludes the occurrence of a neurological disorder

  • cerebral perfusion pressure 70 – 90 mm Hg
  • intracranial pressure 5 – 15 mm Hg or 5 – 10 cm H2O

Tests performed in order to measure the pH and the amount of oxygen (O2) and carbon dioxide (CO2) present in a sample of blood. The results of the tests are used to evaluate lung function and aid to identify an acid-base imbalance. The sample may be taken from arterial or venous blood.


  • pH 7.35 – 7.45
  • PaCO2 35 – 45 mm Hg
  • HCO3 22 – 26 mEq/L
  • O2 saturation 96 – 100%
  • PaO2 85 – 100 mm Hg
  • BE -2 to +2 mmol/L


  • pH 7.31 – 7.41
  • PaCO2 41 – 51 mm Hg
  • HCO3 22 – 29 mEq/L
  • O2 saturation 60 – 85%
  • PaO2 30 – 40 mm Hg
  • BE 0 to +4 mmol/L

To know more about reference ranges for blood tests, click here.


Normal Lab Values: Definition + What High/Low Values Mean

Normal Lab Values: Definition + What High/Low Values Mean

You just got your lab test results back and your doctor tells you that all your tests were normal. Or maybe there were a couple of tests that fell outside the normal range.

But what does “normal” mean and what does it mean if you’re outside this range? Read on to find out more about normal lab values, how normal reference ranges are created, why normal doesn’t always mean healthy, and why normal ranges differ between labs.

What Are Normal Lab Values?

In most cases, normal lab values are a range of values that 95% of a healthy population falls into. However, there are some exceptions to this. For example, for markers of heart damage called troponins, 99% of the healthy population have values that fall within the normal range [1].

Normal ranges are commonly referred to as reference ranges or reference intervals by labs and healthcare providers. Doctors use them to interpret their patients’ lab test results, help make a diagnosis, or decide on treatment [1, 2].

In the context of lab test results, “normal” does not mean usual, typical, or ordinary. Instead, “normal” refers to how these values line up on a graph and form a range. The word “normal” here means a “normal distribution”, or set, of lab values. When we graph this, it looks the symmetrical, bell-shaped curve seen below.

In a normal distribution, the average value lies in the center. Half of the population will have values that lie on the left side of this average; the other half will have values that lie on the right side.

This accounts for most people (95%). Of course, in real life, the set of lab values taken from a population won’t fit this bell shape perfectly.

But the similarity is close enough to be useful in creating reference ranges for most tests.

Once 95% of the values are accounted for, any remaining ones fall outside of the reference range. These are the 2.5% tails on either end of the curve above. Any lab value that falls in these areas is flagged as abnormal and brought to the attention of your healthcare provider.

In cases where only “low” values of the marker are of interest to doctors and point to a disease or disorder, the reference range will be one-sided on the left with a 5% tail as the abnormal range (instead of the 2.

5% tails on either end). One example of such a test is sperm concentration, where only low values are ly to be of concern to doctors.

In other cases, only “high” values may point to health problems, and the abnormal range will be the 5% tail on the right [3].

How Reference Ranges Are Created

There are different ways to create a reference range, or reference interval, as it is commonly referred to by labs and doctors. The gold standard is to conduct a reference interval study [1].

Reference Interval Studies

A reference interval study analyzes a large number of test results from healthy individuals. These studies are often performed according to established international clinical and laboratory guidelines [1].

The first step is identifying a healthy reference population from which to take samples. The minimum number of people needed is 120, according to the guidelines. The absence of disease should be the main difference between this population and the patients for which the test will be applied [1].

Some tests need to have more than one reference range because of factors that affect the results. For example, men and women have separate ranges for total testosterone levels.

The main factors that determine whether multiple reference ranges are necessary are [1]:

  • Age
  • Sex
  • Reproductive status (puberty, menstrual cycle, stage of pregnancy, and menopause)
  • Race (e.g. prostate-specific antigen in African Americans)
  • The time of day a sample is collected (e.g. random vs. first-morning spot urine sample)

Reference interval tests should be performed exactly the same way as in the lab. The time of day for sample collection, sample handling (such as the amount of time before the sample is analyzed), a person’s fasting status – must all be the same [4].

Reference populations are selected from volunteer blood donors, door-to-door contacts, medical students, and hospital outpatients.

Potential participants take health questionnaires to exclude individuals by certain criteria such as physical activity levels, use of medications, medical history, and the presence of certain diseases.

Samples are then taken from those included and the most extreme (outliers) test results removed [3].

The final step is to analyze the lab results and identify the upper and lower limits that 95% of the values fall within [1].

A Posteriori Studies

An alternative to reference interval studies is searching the existing patient data (collected by labs and hospitals and stored in electronic databases) and analyzing it.

This type of analysis is called an “a posteriori” study, meaning that the research is done after (“post”) collecting the information. Since the data is easily accessible, these studies are less costly, less time-intensive, and can include a large number of patient samples.

However, some samples may not come from healthy subjects, especially when it comes to samples from hospitalized patients [2].

Despite these potential drawbacks, multiple a posteriori studies have found relevant and meaningful ranges for evaluating test results [5, 6, 7, 2].

Decision Limits

Certain markers are assigned a decision limit (or multiple decision limits) that is [are] better than reference ranges in making diagnoses and treatment decisions.

A decision limit is a cutoff point where values above or below are linked to an increased risk of developing specific diseases. Their purpose is to indicate when intervention is necessary to prevent disease.

Decision limits may also be doctors’ clinical experience [8].

One test with multiple decision limits is total cholesterol. The upper limits for total cholesterol levels accepted by most labs and doctors are 200 mg/dL and 240 mg/dL.

These limits were established by an expert panel for the National Cholesterol Education Program (NCEP), a program managed by the National Institutes of Health. Levels between 200 mg/dL and 240 mg/dL are associated with a moderate risk of heart disease, while levels above 240 mg/dL are associated with a high risk.

These limits inform doctors on which treatment options to use, such as lifestyle and diet interventions or prescribing statins and other cholesterol-lowering drugs [3].

Other examples of tests with decision limits include blood glucose and HbA1c (a measure of long-term glucose levels) [8].

Why Labs Have Different Reference Ranges

Because there is no universal reference range for most lab tests, ranges will vary from lab to lab. This means that it is possible to get a normal result from one lab and an abnormal result for the same test from another lab, and vice versa.

Reference ranges should be established for each marker by every lab. But the reality is that few labs carry out their own reference interval studies.

Recruiting a healthy reference group and getting their informed consent is expensive and time-intensive, so most labs opt to instead use the reference ranges provided by the test manufacturers.

This is preferable because the lab has to use only 20 sample tests to verify that the manufacturer’s range is accurate. Yet, some labs may skip this step [9, 10].

Labs are faced with numerous challenges when conducting reference interval studies: creating reference ranges for different subpopulations, rare sample types (e.g. cerebrospinal fluid), and tests that require multiple measurements [9].

Sometimes labs will use ranges established from previously published reference interval studies or even use ranges established by other labs [9].

Pros of Reference Ranges

Reference ranges are useful because they provide fixed values from reasonably healthy populations that healthcare providers can compare patient lab results to. This allows them to make informed diagnostic and treatment decisions.

Reference ranges are also appealing to patients (even if they may not know exactly what they mean) because they can see where their results fall in relation to upper and lower limits.

Cons of Reference Ranges

Reference ranges have some drawbacks. First, they do not take into account the results of large population research. This research can reveal different limits for an increased risk of mortality and disease. Decision limits are sometimes better for this reason.

Also, reference ranges do not leave much room for nuance and grey areas. Health is not a black and white phenomenon but instead exists on a spectrum.

Reference ranges do not take into account the uniqueness of and day-to-day, year-to-year variation in each person’s biology, environment, and genetics.

Instead, they are arbitrary cutoffs how lab values are spread out across a “healthy” population, which is hard to define.

A reference population may still contain people with an undiagnosed disease or condition that affects their lab test results.

What Does it Mean if My Lab Value is Outside the Normal Range?

Just because your lab value is outside the normal range does not mean that you necessarily have a disease or disorder. Indeed, and by definition, 5% of healthy individuals will have levels outside of the normal range.

Conversely, a normal lab value does not guarantee the absence of a disease or disease process.

It is important that your healthcare providers examine your lab results in relation to one another. They should also take into account your medical and family history as well as any previous test results (to identify trends).

It’s also important that the lab result is interpreted in light of the reason for requesting the test, such as a routine health check, managing a disease, or making sense of your overall symptoms.

For example, a provider may interpret the same total cholesterol value of 241 mg/dL differently for two patients if one has no history of heart disease, and the other previously suffered a heart attack and is on statins. The provider may be inclined to retest the patient with no past history of heart disease, but continue or increase the current statin dosage for the patient with heart disease.

Another important consideration is how far outside the normal range your lab test result is. For example, sodium concentrations in the blood are kept in a tight range. Lab results that are even slightly too high or too low can be dangerous even in the short-term [11].

For most tests, if your result is slightly outside of the normal range or the abnormal result doesn’t match the rest of your results, your provider may order additional tests or repeat the same test to confirm it.

Factors that may cause abnormal values despite the absence of a disease or disorder include errors in processing and testing the sample, poor patient compliance in pre-test preparation (e.g.

not fasting or stopping the use of prescription medications), and random fluctuations in the patient’s biology [8].

Normal Lab Values vs. Optimal Values

A normal reference range sometimes doesn’t give insight into the optimal range for a lab test. There are a couple of reasons for this. The most obvious reason is that by its very nature and design, a reference range is not intended to capture the optimal range. It is simply an interval that is samples from a pre-defined population.

Another reason reference ranges don’t provide any information on optimal values is because they rarely take into account research on the risk of developing certain diseases.

Lastly, the reference population may not have optimal levels. If the reference population isn’t sufficiently healthy, then this is reflected in the reference range.

Read more about optimal ranges here.


It is important that you mention any medications you may be taking to your healthcare provider as well as any other factors you think may affect your lab results.

To ensure consistency in your test results, you should use the same lab to perform your tests. If you are forced to switch labs, keep in mind that different labs may use different methods of testing your sample or have different reference ranges.


Hematocrit Blood Test: Normal, High, Low Ranges & Results

Normal Lab Values: Definition + What High/Low Values Mean

Picture of Red Blood Cells

The hematocrit blood test determines the percentage of red blood cells (RBC's) in the blood. Blood is composed mainly of red blood cells and white blood cells suspended in an almost clear fluid called serum.

The hematocrit test indicates the percentage of blood by volume that is composed of red blood cells. The condition called “anemia” results from having too few red blood cells. Anemia causes a variety of symptoms.

The hematocrit is a basic test that can tell a physician a lot about a person's health. 

How Is the Hematocrit Measured?

In most labs, the hematocrit is measured by a machine that automatically determines a variety of blood tests referred to as the blood count (CBC). The complete blood count is a numerical listing of the hematocrit, as well as the hemoglobin concentration, and the three blood cell lines produced by the bone marrow (the red blood cells, the white blood cells, and the platelets).

Another simple method is termed the spun hematocrit or “spun crit.” A small amount of blood (about 0.05 to 0.1ml) is placed in a thin capillary tube, the tube is sealed with wax or clay, and then placed in a centrifuge to be spun.

The red cells collect at the bottom and form a red column and are separated from the straw-colored serum column by a small area composed of white blood cells. The height of the total blood in the capillary tube (red cells, white cells and serum equals 100%).

The height of the red cell column divided by the height of the total fluid in the capillary tube equals the hematocrit (percentage of RBC's in the total blood volume). This test can be performed in a few minutes.

What Is a Normal Hematocrit?

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Normal values for the hematocrit test vary according to age, sex, pregnancy, altitude where people live, and even vary slightly between various testing methods. The following are reported ranges of normal hematocrit levels:

  • Newborns: 55%-68%
  • One (1) week of age: 47%-65%
  • One (1) month of age: 37%-49%
  • Three (3) months of age: 30%-36%
  • One (1) year of age: 29%-41%
  • Ten (10) years of age: 36%-40%
  • Adult males: 42%-54%
  • Adult women: 38%-46%
  • Adult pregnant women: about 30% – 34% lower limits and 46% upper limits
  • High Altitude residents: about 45% – 61% in males; 41% – 56% in females (These levels gradually average higher as the altitude where people live increases. This is a result of the increased demand for the oxygen-carrying capacity of red blood cells at higher altitudes where there is decreased oxygen concentration in the atmosphere.)

These values may vary from authorities in the field by as much as 7%. Consequently, it is best to have a doctor explain the significance of an individual's level of hematocrit if it is not normal.

Health Screening Tests Every Woman Needs See Slideshow

What Does a Low Hematocrit Mean?

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A low hematocrit means the percentage of red blood cells is below the lower limits of normal (see above) for that person's age, sex, or specific condition (for example, pregnancy or high-altitude living). Another term for low hematocrit is anemia. Causes of low hematocrit, or anemia, include:

What Does a High Hematocrit Mean?

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A high hematocrit means the percentage of red blood cells in a person's blood is above the upper limits of normal (see above) for that person's age, sex, or specific condition (for example, pregnancy or high altitude living). Causes of a high hematocrit include:

How Is a Low or High Hematocrit Treated?

The treatment of high or low hematocrit depends on the underlying cause(s), the hematocrit level, and the overall health status of the individual. Most people are not treated with medications or procedures if the hematocrit is only slightly above or below the normal levels.

Some patients with very low hematocrits may require intravenous iron, transfusions or medications to stimulate the production of red cells by the bone marrow.

Some patients with very high hematocrits due to diseases, such as polycythemia rubra vera, may require blood letting (blood removal).

The patient's doctor will decide when medication or procedures are necessary for each particular individual. In general, abnormal hematocrit values are monitored by doctors with routine blood testing.

Reviewed on 9/3/2019


Medically reviewed by John A. Daller, MD American Board of Surgery with subspecialty certification in surgical critical care REFERENCES: “PedNSS Health Indicators.” Blood Products Advisory Committee. Topic II: Iron Status in Blood Donors.

Nabili, Siamak N. MD, MPH. “Complete Blood Count (CBC).” Updated Jan 24, 2014.

Shiel, William C. Jr., MD, FACP, FACR. “Hematocrit.” Updated Oct. 19, 2015.


Reference Ranges and What They Mean

Normal Lab Values: Definition + What High/Low Values Mean

NOTE: This article is research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board.

This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

To access online sources, copy and paste the URL into your browser.

Sources Used in Current Review

Barth JH. Editorial: Reference Ranges Still Need Further Clarity. Annals of Clinical Biochemistry. 2990;46:1-2.

Boyd JC. Defining Laboratory Reference Values and Decision Limits: Populations, Intervals, and Interpretations. Asian Journal of Andrology. 2010;12: 83–90.

Ceriotti F. Prerequisites for Use of Common Reference Intervals. Clinical Biochemistry Review. 2007;28:115-121.

Ceriotti F, Henny J. Are my laboratory results normal? Considerations to be Made Concerning Reference Intervals and Decision Limits. Pediatric Reference Intervals. 2008;19:1-9.

Jones G, Barker A. Reference Intervals. Clinical Biochemistry Review. 2008;29 (Suppl i):S93-S97.

Phillips P. Pitfalls In Interpreting Laboratory Results. Australian Prescriber. 2009;32:43-46.

(2009) Determining Laboratory Reference Intervals: CLSI Guideline Makes the Task Manageable. Available online at Accessed August 2015.

(December 11, 2013) National Cancer Institute. Understanding Laboratory Tests. Available online at Accessed August 2015.

Graham Jones, Antony Barker. Reference Intervals. Clin Biochem Rev. 2008 Aug; 29(Suppl 1): S93–S97. Available online at Accessed August 2015.

(July 2012) Al-Borai A. Frequently-Asked-Questions on Reference Intervals and Biological Variation. Westgard QC. Available online at Accessed August 2015.

Sources Used in Previous Reviews


Clinical Diagnosis and Management by Laboratory Methods. 20th ed. Henry JB, ed. New York: Saunders: 2001.

Laboratory Medicine: Test Selection and Interpretation. Howanitz JH and Howanitz PJ, eds. New York: Churchill Livingstone; 1991:6-8.

National Committee for Clinical Laboratory Standards. How to Define and Determine Reference Intervals in the Clinical Laboratory: Approved Guideline. 2nd ed. Wayne, PA: 2000.

Sacher RA, McPherson RA, Campos J. Widmann's Clinical Interpretation of Laboratory Tests. 11th ed. Philadelphia: F.A. Davis Company; 2000:10-17.

The Science of Laboratory Diagnosis. Crocker J and Burnett D, eds. Oxford: Isis Medical Media; 1998: 391-4.

Tietz Textbook of Clinical Chemistry. Burtis CA and Ashwood ER, eds. Philadelphia: W. B. Saunders Company; 1994: 454-464.

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. St. Louis: Elsevier Saunders; 2006. Pp. 425-437.

McClatchey, et al. Clinical Laboratory Medicine. Second Edition.

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, Fourth Edition.