(133) Comparative Analysis of HemoCue Versus a Colorimetric Assay to Measure Cell-Free Plasma Hemoglobin

Introduction: Hemolysis is a frequent sequela of extracorporeal therapies, resulting in the release of cell-free plasma hemoglobin (PHb). PHb and its degradation products are known for their toxicity and contribution to organ dysfunction. Despite this, laboratory measurement of PHb in the clinical setting is often limited or delayed. Consequently, this makes the study of hemolysis in a research setting additionally challenging, particularly when involving multiple institutions. Thus, we provide a comparative analysis of the ability of the rapid HemoCue® system to detect clinically significant hemolysis, defined as levels ≥50mg/dL, as compared to an established PHb colorimetric assay available in the laboratory of the UPMC Children’s Hospital of Pittsburgh.

Methods: Blood samples were taken from 88 pediatric patients undergoing cardiopulmonary bypass for cardiac surgery at the UPMC Children’s Hospital of Pittsburgh at 5 time points. Samples were immediately centrifuged after which plasma was separated and then analyzed by the HemoCue® system, which utilizes a modified azidemethemoglobin reaction contained within a commercially available microcuvette to measure PHb. An aliquot was simultaneously sent to the clinical laboratory for analysis by a colorimetric assay that utilizes the peroxidase activity of PHb to produce a chromogenic oxidized product.

Results: A total of 419 paired samples were analyzed. PHb measured via the HemoCue® and the clinical laboratory were correlated (rho 0.78, p<.00001). Using critical PHb levels (50 mg/dL as measured by the clinical laboratory) as a binary outcome, the area under the receiver operating characteristic curve was 0.95 (95% CI 0.92-0.98), indicating excellent diagnostic performance of the HemoCue® to be able to determine clinically significant hemolysis.

Conclusions: The reliable measurement of PHb is an important prerequisite to the study of hemolysis as well as to the initiation of interventions to minimize its effects. The HemoCue® Low Hb/Plasma system shows the ability to identify actionable levels of hemolysis and may represent an alternative and less cumbersome method for the measurement of PHb.