Analytical artifacts in hematocrit measurements by whole-blood chemistry analyzers

Abstract

Compact analyzers suited to near-patient testing estimate hematocrit by measuring the conductivity of undiluted blood. We evaluated the accuracy 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, the BGE analyzer correlated well with both EPC and PCV hematocrit determinations (BGE = 1.00 PCV + 0.3%, S(y)/x = 2.0%), suggesting that all three methods are similar in performance for most patients. However, a patient with increased plasma osmolality showed significant decreases in BGE and PCV hematocrits relative 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 cardiac surgery, whose blood had large changes in protein concentration, showed discrepancies between hematocrits by conductivity and other methods; similar effects could be produced by changes in protein concentration or in vitro addition of polyethylene glycol. We conclude that conductivity measurements provide accurate hematocrit results for physiologically normal subjects but not for some intensive-care and surgical patients.

Where are we at with point‐ of‐ care testing in haematology?

“…One of the most frequently used methods for measuring Hb in ICU or during surgical interventions is via the blood‐gas analysers, based on either conductivity or spectrophotometry. Although conductivity‐based POCT devices provide accurate Hct results in normal subjects (Stott et al , ), results can be erroneously low or high during haemodilution or the alteration of plasma proteins, electrolytes or triglycerides. Discrepancies of up to 20 g/l for Hb and 4% for Hct have been reported (Hopfer et al , ).…”

“…Discrepancies of up to 20 g/l for Hb and 4% for Hct have been reported (Hopfer et al , ). As these dynamic changes are likely to occur during surgery or ICU, the conductivity‐based POCT results should be interpreted with caution in these circumstances (McMahon & Carpenter, ; Stott et al , ; McNulty et al , ; Hopfer et al , ; Stadlbauer et al , ). A downward bias has been demonstrated when the Hct is below 30% (al‐Odeh et al , ).…”

Point-of-Care Versus Central Testing of Hemoglobin During Large Volume Blood Transfusion

“…They reported a bias of only 2.78%, which was surprisingly lower than all other POC devices they evaluated, even with the hematocrit result range varying widely from 24 to 45% [10]. These authors did not have an explanation for why the bias was so much lower for the EPOC® device's hemoglobin in their study, especially since it was not consistent with the results of the other POC devices they had tested which utilized similar technology or prior literature that demonstrated that other POC devices using conductometric hemoglobin measurements were not that accurate in similar patient populations [10,[17][18][19].…”

In vitroandin vivoevaluation of blood coagulation activation of polyvinyl alcohol hydrogel plus dextran-based vascular grafts

“…This phenomenon is explained by the overestimation of true volume of erythrocytes due to the entrapment of plasma in the cellular layer. 79 Also the contribution of leukocytes and platelets for the total volume of erythrocytes can be considered, however, their volume in practice is neglected. 79 These results suggest that intravascular hemolysis was negligible and cannot be attributed to PVA vascular grafts as proved before at in vitro hemolysis testing that considered this biomaterial as non-hemolytic (data not shown).…”

“…79 Also the contribution of leukocytes and platelets for the total volume of erythrocytes can be considered, however, their volume in practice is neglected. 79 These results suggest that intravascular hemolysis was negligible and cannot be attributed to PVA vascular grafts as proved before at in vitro hemolysis testing that considered this biomaterial as non-hemolytic (data not shown). In fact in vitro hemolysis testing correlates well with the in vivo findings and most of altered erythrocyte morphology observed by implantation of vascular grafts was related to altered blood flow rather than by incompatible blood-material interactions.…”