Errors of measurement for blood volume parameters: a meta-analysis

Abstract

The volume of red blood cells (VRBC) is used routinely in the diagnostic workup of polycythemia, in assessing the efficacy of erythropoietin administration, and to study factors affecting oxygen transport. However, errors of various methods of measurement of VRBCand related parameters are not well characterized. We meta-analyzed 346 estimates of error of measurement of VRBCfor techniques based on Evans blue (VRBC,Evans),51chromium-labeled red blood cells (VRBC,51Cr), and carbon monoxide (CO) rebreathing (VRBC,CO), as well as hemoglobin mass with the carbon-monoxide method (MHb,CO), in athletes and active and inactive subjects undergoing various experimental and control treatments lasting minutes to months. Subject characteristics and experimental treatments had little effect on error of measurement, but measures with the smallest error showed some increase in error with increasing time between trials. Adjusted to 1 day between trials and expressed as coefficients of variation, mean errors for MHb,CO(2.2%; 90% confidence interval 1.4–3.5%) and VRBC,51Cr(2.8%; 2.4–3.2%) were much less than those for VRBC,Evans(6.7%; 4.9–9.4%) and VRBC,CO(6.7%; 3.4–14%). Most of the error of VRBC,Evanswas due to error in measurement of volume of plasma via Evans blue dye (6.0%; 4.5–7.8%), which is the basis of VRBC,Evans. Most of the error in VRBC,COwas due to estimates from laboratories with a relatively large error in MHb,CO, the basis of VRBC,CO. VRBC,51Crand MHb,COare the best measures for research on blood-related changes in oxygen transport. With care, VRBC,Evansis suitable for clinical applications of blood-volume measurement.