Prediction of red cell and blood volumes distribution by various nomograms: do current nomograms overestimate?

Background: Currently used formulas for estimation of a person's red cell volume (RCV) by weight and height are decades old and were based on the use of 51Cr isotopes and on a sample population, which may not be reflective of today's population. In this study, the accuracy and precision of the use of 99mTc RCV measurements in volunteers more typical of today's population were evaluated.

Study Design And Methods: The subjects were volunteers who met the requirements for a standard blood donation.

Results: The mean +/- standard deviation (SD) 99mTc RCV for 127 males (mean weight, 83.2 kg; height, 180 cm) was 2062 +/- 339 mL, and for 101 females (mean weight, 69.5 kg; height, 166 cm) it was 1320 +/- 201 mL. These results were highly correlated with RCV results with the standard extrapolation 51Cr method with stored red blood cells (RBCs) and highly consistent (within +/-10%) by repeated measurements with the same 22 donors over a 3.5-year period. The RCV results correlated with estimates from the current formulas, but were on average 11 to 14 percent lower.

Conclusion: The studies demonstrated that 99mTc is a reproducible and precise method for determination of a person's RCV and that current formulas may significantly overestimate the RCV of today's population. This is likely the result of a shift in population characteristics over the past four decades as reflected by an increased mean body mass index (from 25 to 28 kg/m2), which has not resulted in a proportionally increased RCV.