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.

Myeloproliferative Disease: Polycythemia Vera: The Packed Cell Volume and The Curious Logic of The Red Cell Mass.

Since the first systematic blood volume studies of polycythemia in the 1920s, measurement of blood volume and red cell mass (RCM) has become routine. However, the radionuclide-labeling methods promulgated by the International Committee for Standardization in Haematology (ICSH) remain complex and poorly understood. Many hematologists and other clinicians err in the belief that these methods permit "direct measurement" of RCM, whereas the ICSH method is indirect: it requires calculation of RCM from (PCV) x (whole blood volume). The use of an elevated value of PCV to calculate RCM in order to evaluate the same elevated value of PCV is a curiously circular logic that is embraced by most clinicians and most hematologists. Analysis of published data in 186 cases of polycythemia vera indicates that RCM is an exponential function of PCV. In most cases, PCV alone suffices to document normal or increased RCM. Relative polycythemia results from dehydration, not from stress. Clinicians need to be aware of the range of physiologic fluctuations that normally occur in plasma volume. Realistic criteria for normal ranges of PCV, Hb concentration and RCM should be adopted in clinical laboratories so that clinicians will not be misled to undertake futile and costly investigations of results that are in the upper percentiles of the normal distribution, as exemplified by the Ulysses Syndrome.