Hematocrit Test
Also known as: Hct, HCT, Packed Cell Volume, PCV
What is Hematocrit?
Hematocrit is the percentage of your blood that is made up of red blood cells. It reflects the proportion of blood composed of oxygen-carrying cells.[MedlinePlus (NIH)]
What This Test Measures
This test measures the ratio of the volume of red blood cells to the total volume of blood, expressed as a percentage.[Mayo Clinic]
Why It's Important
Hematocrit helps diagnose anemia, polycythemia, dehydration, and other conditions affecting red blood cell levels.[MedlinePlus (NIH)]
It is often used alongside hemoglobin to assess blood oxygen-carrying capacity.[Cleveland Clinic]
Who Should Get This Test?
Hematocrit is routinely measured as part of a complete blood count.
Risk Factors
- Symptoms of anemia (fatigue, weakness, shortness of breath)
- History of bleeding disorders or heavy menstruation
- Chronic kidney disease
- Heart or lung conditions
- Living at high altitude
- Dehydration symptoms
- Before or after major surgery
- Athletes monitoring performance
Screening Schedule
Part of routine CBC; more frequent monitoring during pregnancy, for athletes, or when managing anemia.
What Happens During the Test
A blood sample is drawn from a vein or fingerstick. Modern analyzers calculate hematocrit from the measured red blood cell count and mean cell volume, or it can be measured directly by centrifuging blood.
Duration
5-10 minutes for blood draw; results typically available same day
Discomfort Level
Minimal discomfort from needle insertion
Risks & Side Effects
Standard blood draw with minimal risks.
- •Brief pain at needle site
- •Small bruise may develop
- •Rare: lightheadedness if anxious about blood draw
- •Very rare: infection at puncture site
Normal Range
For men: 38.3% to 48.6%. For women: 35.5% to 44.9%.
Note: Normal ranges vary by age, altitude, and pregnancy status.
Source: Mayo ClinicUnit Conversion
Convert between % (L/L) and decimal fraction
| % (L/L) | decimal fraction |
|---|---|
| 35 | 0.35 |
| 40 | 0.4 |
| 45 | 0.45 |
| 50 | 0.5 |
| 55 | 0.55 |
High Values
High hematocrit can be caused by dehydration, smoking, lung disease, living at high altitude, or polycythemia vera. It thickens blood and increases clot risk.[Mayo Clinic]
Low Values
Low hematocrit indicates anemia. Causes include iron deficiency, blood loss, bone marrow problems, chronic disease, and nutritional deficiencies.[Cleveland Clinic]
Test Limitations & Accuracy
Several factors can affect hematocrit accuracy:
- ⚠Dehydration artificially raises hematocrit by reducing plasma volume
- ⚠Overhydration can falsely lower hematocrit
- ⚠Recent blood transfusion affects accuracy
- ⚠Pregnancy normally decreases hematocrit due to plasma expansion
- ⚠High altitude living increases hematocrit over time
- ⚠Time of day and body position during draw can affect results
- ⚠Very high white cell counts can interfere with measurement
Alternative & Complementary Tests
Hematocrit is typically evaluated alongside other CBC components:
Primary measure of oxygen-carrying capacity; often correlates with hematocrit
To count actual number of red cells
To determine red cell size and classify anemia type
To assess bone marrow red cell production
To evaluate iron deficiency as cause of low hematocrit
Frequently Asked Questions
What is the difference between hematocrit and hemoglobin?
Hemoglobin measures the actual amount of oxygen-carrying protein in blood (in g/dL), while hematocrit measures the percentage of blood volume occupied by red blood cells. Both assess anemia but from different angles.
Source: Mayo ClinicReferences
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Medical Disclaimer
This information is for educational purposes only and is not intended as medical advice. Always consult with a qualified healthcare provider for interpretation of test results and medical decisions.
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