Interpretation of measured red cell mass in the diagnosis of polycythaemia.

Expression of predicted and measured red cell mass (RCM) in terms of ml/kg body wt. lacks precision. The use of formulae for prediction of normal mean red cell mass derived from the blood volume prediction (BV) of Nadler et al (1962) has been examined. It is proposed that a more accurate determination of mean normal predicted red cell mass (MNRCM) is obtained by using: 0.47 X 0.91 X BV = MNRCM for males; 0.43 X 0.91 X BV = MNRCM for females. The MNRCMs given by these formulae agree with those given by predictions based on lean body mass and surface area. Examination of the '95% confidence limits' of the 'Nadler' prediction indicates that males with measured RCMs greater than 25% and females with measured RCMs greater than 30% above their MNRCM may be regarded as having polycythaemia.