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