Red cell mass and plasma volume measurements in polycythemia: evaluation of performance and practical utility.

BACKGROUND: Despite the absence of any systematic evidence for diagnostic utility, red cell mass (RCM) measurement has been endorsed as a major diagnostic criterion for polycythemia vera (PV) based on a set of eligibility criteria for a clinical trial formulated by an International PV Study Group in 1967.

METHODS: A retrospective analysis was performed on a consecutive series of 105 patients who underwent blood volume measurements for evaluation of polycythemia. In a previous study, the authors had systematically compared RCM measurement by 51Cr-labeled erythrocytes and 125I-labeled human serum albumin and demonstrated equivalence between the two methods. In the current study, they used the latter method and applied the International Committee for Standardization in Haematology recommendations for result interpretation in order to evaluate test performance and practical utility.

RESULTS: RCM exceeded the 98-99% limits of the reference range in 76%, 20%, 22%, and 57% of patients with PV (n = 25), secondary polycythemia (n = 35), spurious or apparent polycythemia (n = 38), and essential thrombocythemia (n = 7), respectively. Decreased plasma volume was rarely seen in any of the disease categories. In all instances of PV, the diagnosis was readily apparent, based on alternative clinical and laboratory tests, and did not require the additional information from blood volume measurement. Furthermore, alternative methods of PV diagnosis, based on disease-specific biological markers as well as bone marrow histology, are now available.

CONCLUSIONS: The continued use of RCM and plasma volume measurements for the diagnosis of PV is no longer warranted.