Normal value of hematocrit
Hematocrit (Hct) is the percentage of red blood cells in total blood volume. Normal ranges vary by sex and age:
- Adult males: 40-54%
- Adult females: 36-48%
- Newborns: 44-64% (higher due to fetal hemoglobin)
- Children (varies by age): roughly 30-44%
A quick rule of thumb: Hct is approximately 3x the hemoglobin value.
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I need to find Table 66-2 which has the normal hematocrit values by age and sex:
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Here is the complete, authoritative answer from Harrison's Principles of Internal Medicine (22nd ed., 2025):
Normal Hematocrit Values
Hematocrit (Hct) is the percentage of packed blood volume occupied by intact red blood cells (RBCs) after centrifugation. It is calculated as:
Hct = (RBC count × MCV) / 10
A quick clinical rule: Hct ≈ 3 × hemoglobin (g/dL)
Normal Values by Age, Sex & Physiological State
(From Harrison's Principles of Internal Medicine, 22nd ed., Table 66-2)
| Age / Sex / State | Hemoglobin (g/dL) | Hematocrit (%) |
|---|---|---|
| At birth | 17 | 52 |
| Childhood | 12 | 36 |
| Adolescence | 13 | 40 |
| Adult man | 16 ± 2 | 47 ± 6 (range: ~41-53%) |
| Adult woman (menstruating) | 13 ± 2 | 40 ± 6 (range: ~34-46%) |
| Adult woman (postmenopausal) | 14 ± 2 | 42 ± 6 (range: ~36-48%) |
| During pregnancy | 12 ± 2 | 37 ± 6 (range: ~31-43%) |
Key Points
- Males have a higher Hct than females due to testosterone stimulating erythropoiesis.
- Newborns have the highest Hct (~52%) because of high fetal hemoglobin and the hypoxic intrauterine environment.
- Pregnancy causes a physiological drop in Hct due to plasma volume expansion (dilutional effect).
- Altitude also affects Hct - people living at high altitudes have higher values due to chronic relative hypoxia.
- Hct is used alongside hemoglobin to define anemia (Hct below the lower limit of normal for age/sex).
Sources: Harrison's Principles of Internal Medicine 22E (2025), Table 66-2; Frameworks for Internal Medicine
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