Measurement of blood volume and red cell mass: Re-examination of ⁵¹Cr and ¹²⁵I methods

Comparison of results of red cell mass (RCM) measurement by ⁵¹Cr and ¹²⁵I methods in 119 patients showed virtual equivalence. Both methods have an acceptable coefficient of variation (CV) that is <5%. The ¹²⁵I method is simpler and much less expensive. Unrealistically narrow 'normal ranges' for RCM are likely to lead to misdiagnosis of polycythemia vera. Upper normal limits of 39 mL/kg (males) and 32 mL/kg (females) are consistent with originally published data in normal persons; use of these limits as criteria would reduce the risk of misdiagnosis. No cases of 'stress erythrocytosis' or Gaisbock Syndrome were encountered among the 119 cases reviewed.