A review of methodology and normal ranges for the estimation of red cell and plasma volume

Abstract

Aim The aim of this study was to audit current procedures for the measurement of red cell volume (RCV) and plasma volume (PV) against ICSH (International Council for Standardisation in Haematology) guidelines. Method Eighty-nine measurements of RCV and PV were categorized according to three normal ranges: (1) Retzlaff's height and weight formula; (2) weight only formula; and (3) ICSH recommendations. Results Twelve patients who had a raised RCV using Retzlaff's formula fell into the ICSH normal range. Clinical follow-up has so far been obtained on seven of these patients; all were treated conservatively. Categorization of RCV by weight only formula differed from the ICSH method in 21 cases. In 14 patients with a BMI>29 kg·m−2 there was a difference between the two methods in 9 (64%) cases. Departures from the ICSH recommendations for blood sampling, resulting in an error of 5% in measured PV, and differences in the correction factors applied at the two hospitals were also investigated. Weight only based normal ranges under-diagnose polycythemia in obese subjects whilst both the Retzlaff and ICSH ranges appear to be independent of obesity. Patients diagnosed as having a raised RCV using the Retzlaff formula who were within the ICSH normal range were treated conservatively, suggesting that the Retzlaff range is too narrow. Conclusion This study demonstrates the importance of reviewing established procedures against current standards.