Red Cell Mass: The Sleeping Beauty

Abstract

Objective: One of the more neglected procedures in nuclear medicine is the radioisotopic determination of red cell mass (RCM) which is a valuable, cost-effective and easily performed procedure that helps establish the diagnosis of true polycythemia and distinguish it from relative erythrocytosis. Early diagnosis of polycythemia is important since a delay in treatment may be associated with serious complications.

Methods: Whole blood (15–25 ml) was withdrawn and added to a small volume of ACD solution. Chromate-51 (1.48–1.85 MBq) was added to the blood with continuous mixing at 37°–39°C. After incubation, ascorbic acid (50–100 mg) was added to reduce the ⁵¹Cr to the trivalent state and stop it from binding to the red cells. The blood was reinjected into the patient and a whole-blood sample was drawn from a different vein at 45 min postinjection. The aliquots from the sample were washed three times in saline and then counted.

Results: If the RCM exceeds the predicted mean normal value by more than 12.5%, the patient is thought to have a high-normal RCM, which may be a physiologic variable, transient anomoly or an early stage of an absolute polycythemia.

Conclusions: Although many labaratories express the results of RCM in terms of ml/kg body weight, this approach may be inaccurate for the individual patient. Based on the literature, a more accurate and practical method of predicting and interpreting RCM is presented.