Diurnal, postural and postprandial variations of hematocrit.

The microhematocrit (HCT) values of 59 subjects increased significantly in the sitting position and after moderate exercise, in comparison with the values obtained during recumbency. The consumption of an 800-calorie meal decreased the HCT and this effect lasted for six hours. In order to obtain comparable results blood for HCT should be taken in a "standard basal condition" in the morning hours, in the fasting state or after a light breakfast, and the patient should sit for at least 30 minutes before the blood specimen is taken.