Red cell volumes computed from the radioiodinated serum albumin (RISA) technique and the peripheral venous hematocrit almost always result in values that are high compared to those of the Cr51 red cell method because of the phenomenon of plasma skimming. A formula for the calculation of a correction factor was derived, and values of the factor as a function of venous hematocrit for an assumed ratio of body hematocrit / venous hematocrit = 0.87 are presented. Application of the correction factor to the RISA red cell volume in 58 patients resulted in an extraordinarily high degree of correlation (r=.970) with Cr51 red cell method, and the regression line and the line of identity were nearly indistinguishable; there was neither a statistical nor practical difference between results of both methods. The corrected RISA red cell volume may therefore be used as a good estimate of the true red cell volume in calculating red cell deficits or transfusion requirements when the Cr51 red cell technique is either unavailable or impractical.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging