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Subject: Hematocrit (Hct)
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Hct is the ratio of spun RBCs to plasma, reflecting the volume of packed RBCs. It may be performed manually following centrifugation or calculated in automated counters as the product of MCV and the RBC count. It is expressed as a percentage.
Normal range (adults): 37–47% for women and 42–52% for men.
Abnormalities in Hct levels parallel those for Hb.
Errors may occur in patients with polycythemia vera, as well as in those with very high WBC counts because of an elevated buffy coat, with RBC agglutination, and with large platelets. These errors are more marked in the manual methods.
Errors in both methodologies may also occur in patients with abnormal plasma osmotic pressure. Such errors are minimized with the current generation machines.
Technical errors in blood preparation may also result in false values (see “Hemoglobin” below). In blood kept at room temperature for more than 6 hours, the Hct and MCV are elevated due to swelling of RBCs, whereas cell counts and indices are stable for 24 hours.