ANALYTICAL ARTIFACTS IN HEMATOCRIT MEASUREMENTS BY WHOLE-BLOOD CHEMISTRY ANALYZERS

Compact analyzers suited to near-patient testing estimate hematocrit b y measuring the conductivity of undiluted blood. We evaluated the accu racy of hematocrit determination of one such analyzer (Instrumentation Laboratory BGE Analyzer) against an automated cell counter (EPC) and packed cell volume (PCV) microhematocrit. When specimens (n = 34) from outpatient and ward patients were analyzed with all three methods, th e BGE analyzer correlated well with both EPC and PCV hematocrit determ inations (BGE = 1.00 PCV + 0.3%, S-y/x = 1.6%; BGE = 1.04 EPC + 0.4%, S-y/x = 2.0%), suggesting that all three methods are similar in perfor mance for most patients. However, a patient with increased plasma osmo lality showed significant decreases in BGE and PCV hematocrits relativ e to the EPC method. The differences in hematocrit measurements could be reproduced by adding solutes to blood in vitro or by modifying the plasma osmolality of rats in vivo. Samples from patients undergoing ca rdiac surgery, whose blood had large changes in protein concentration, showed discrepancies between hematocrits by conductivity and other me thods; similar effects could be produced by changes in protein concent ration or in vitro addition of polyethylene glycol. We conclude that c onductivity measurements provide accurate hematocrit results for physi ologically normal subjects but not for some intensive-care and surgica l patients.