What Is Hematocrit (HCT) in a Blood Test?
Hematocrit (HCT) measures the percentage of your blood volume made up of red blood cells. If your HCT is 45%, that means 45% of your blood is red cells.
Normal Ranges
- Men: 38.8–50.0%
- Women: 34.9–44.5%
- Roughly 3× hemoglobin value (Hgb 15 ≈ HCT 45%)
Low Hematocrit Causes
- Anemia — any cause
- Blood loss
- Pregnancy — plasma expansion dilutes red cells
- Bone marrow suppression
- Nutritional deficiencies
High Hematocrit Causes
- Dehydration — plasma decreases, red cells concentrate
- Chronic lung disease
- High altitude
- Smoking
- Polycythemia vera
- Testosterone use
Key Relationship
- HCT ≈ 3 × Hemoglobin
- Significant discrepancy suggests lab error or abnormal red cell condition
Source: NLM MedlinePlus, American Association for Clinical Chemistry.
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