Hematocrit
HCT· also: Hct, Packed Cell Volume, PCV
Clinical Overview
Hematocrit (HCT) measures the percentage of blood volume made up of red blood cells. It reflects the overall red cell mass and is used alongside hemoglobin and RBC count to assess anemia and polycythemia. Hematocrit is approximately three times the hemoglobin value in most clinical situations.
Why This Test Matters
Hematocrit is particularly useful in managing patients with fluid balance disorders. In dehydration, hematocrit rises because plasma volume decreases while red cell mass stays the same. In overhydration or pregnancy, hematocrit falls without any true decrease in red cells. For assessing true anemia, hemoglobin is generally the preferred measurement.
Reference RangesWHO/IFCC standards
| Age Group | Sex | Reference Range | Unit | Notes |
|---|---|---|---|---|
| Adults (18–64) | Male | 41 – 53 | % | — |
| Adults (18–64) | Female | 36 – 46 | % | — |
| All ages | Female | 33 – 42 | % | Pregnancy |
Also reported in: L/L.
Critical (Panic) Values
Critical Low: < 21 %. Critical High: > 60 %. Values outside these limits require immediate clinical attention.
What Causes Abnormal Results?
High HCT Causes
- Dehydration (most common cause)
- Polycythemia vera
- Chronic hypoxia (COPD, high altitude)
- Heavy smoking
- Burns (plasma loss, relative rise)
- Erythropoietin misuse
Low HCT Causes
- Iron deficiency anemia
- Overhydration or IV fluid administration
- Pregnancy (physiological hemodilution)
- Hemolytic anemia
- Bone marrow failure
- Chronic kidney disease
Signs & Symptoms to Watch For
How to Prepare for This Test
No special preparation. Part of a routine CBC. Lying down for extended periods before blood draw can slightly lower hematocrit compared to standing, due to fluid redistribution.
Factors That Can Affect Results
- Dehydration (raises hematocrit)
- Pregnancy (lowers hematocrit through hemodilution)
- Posture (lying vs standing affects plasma distribution)
- Recent IV fluids (lowers hematocrit)
- Sample hemolysis (can falsely alter result)
Related Topics
Frequently Asked Questions
What is the difference between hematocrit and hemoglobin?
Hematocrit measures what fraction of blood volume is red blood cells (expressed as a percentage), while hemoglobin measures the actual amount of hemoglobin protein (in g/dL). As a rough rule, hematocrit (%) ≈ 3 × hemoglobin (g/dL). Both tests reflect anemia, but hemoglobin is generally more clinically accurate for assessing oxygen-carrying capacity.
Can a hematocrit of 60% be normal?
A hematocrit of 60% is above the critical high threshold and is never considered normal. At this level, blood viscosity is significantly increased, raising the risk of thrombosis (blood clots), stroke, and cardiovascular events. Investigation for polycythemia vera or severe secondary erythrocytosis is required.