Estimated plasma volume status is a modest predictor of true plasma volume excess in compensated chronic heart failure patients

Plasma volume and especially plasma volume excess is a relevant predictor for the clinical outcome of heart failure patients. In recent years, estimated plasma volume based on anthropometric characteristics and blood parameters has been used whilst direct measurement of plasma volume has not entered clinical routine. It is unclear whether the estimation of plasma volume can predict a true plasma volume excess. Plasma volume was measured in 47 heart failure patients (CHF, 10 female) using an abbreviated carbon monoxide rebreathing method. Plasma volume and plasma volume status were also estimated based on two prediction formulas (Hakim, Kaplan). The predictive properties of the estimated plasma volume status to detect true plasma volume excess > 10% were analysed based on logistic regression and receiver operator characteristics. The area under the curve (AUC) to detect plasma volume excess based on calculation of plasma volume by the Hakim formula is 0.65 (with a positive predictive value (PPV) of 0.62 at a threshold of - 16.5%) whilst the AUC for the Kaplan formula is 0.72 (PPV = 0.67 at a threshold of - 6.3%). Only the estimated plasma volume status based on prediction of plasma volume by the Kaplan formula formally appears as an acceptable predictor of true plasma volume excess, whereas calculation based on the Hakim formula does not sufficiently predict a true plasma volume excess. The low positive predictive values for both methods suggest that plasma volume status estimation based on these formulas is not suitable for clinical decision making.