Determination of the packed cell volume using 131I-human serum albumin

When trace quantities of labelled albumin have been added to blood, the packed cell volume (PCV) may be determined by isotope counting using the relationship: (plasma counts-blood counts)/(plasma counts). This method for measuring the PCV is not affected by plasma trapping between the red cells and the results do not depend upon the centrifugation conditions. The PCV determination with labelled albumin has a high precision (coefficient of variation = 0.9%) and there is very good agreement with the centrifugation PCV using Wintrobe tubes after this measurement has been corrected for plasma trapped between the red cells. No significant compression of the red cells occurred when the blood samples were centrifugated in Wintrobe PCV tubes.