Overestimation of hemoglobin in a patient with an IgA-kappa monoclonal gammopathy

A patient with multiple myeloma had an automated blood count performed on a Coulter STK-S counter that repeatedly failed internal limits for both mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration. The calculated hematocrit agreed with a spun hematocrit, suggesting that the he moglobin concentration was being overestimated by the automated counter. Me asurement of the plasma hemoglobin concentration of the sample, which showe d no visible hemolysis, gave a hemoglobin concentration of 32 g/L on the ST K-S analyzer. Correction of the whole blood hemoglobin using the plasma hem oglobin gave a value consistent with the hematocrit. The corrected mean cor puscular hemoglobin and mean corpuscular hemoglobin concentration values we re within standard limits. This patient's paraprotein was characterized as IgA-kappa and was present at a concentration of 61 g/L. The hemoglobin conc entration measured on whole blood by Sysmex NE 8000 and Technicon H*1E auto analyzers agreed reasonably well with the corrected result from the STK-S.