Glucose determinations in plasma and serum: potential error related to increased hematocrit.

This study reports the effect of increased hematocrit (packed cell volume) on the rate of decrease in plasma glucose during 6 h in blood specimens from seven newborns (cord blood) and heparin-treated blood specimens from eight adults. Mean hematocrits ranged frm 0.43 to 0.75 for the adults and from 0.51 to 0.81 for the infants. The decrease in glucose was related to time and to hematocrit. For example, in adults with a mean hematocrit of 0.43, glucose decreased from 890 +/- 40 mg/L to 570 +/- 30 mg/L (mean +/- SEM) at 6 h, whereas in adults with a mean hematocrit of 0.75, glucose decreased from 890 +/- 40 to 200 +/- 30 mg/L. In infants with a mean hematocrit of 0.51, glucose decreased from 1010 +/- 20 to 480 +/- 70 mg/L at 6 h; infants with a mean hematocrit of 0.81 had blood glucose decrease from 1010 +/- 20 to 50 +/- 30 mg/L. These results indicate that the incidence of hypoglycemia in infants with polycythemia may be overestimated, and emphasize the need for prompt handling of blood samples collected from newborns for glucose determinations.