Calibration of hematology analyzers. Role of the microhematocrit

Discrepancies between the hematocrit values measured by automated methods and those measured by centrifugation have discouraged the use of the centrifuged microhematocrit to calibrate automated hematology analyzers. The discrepancy appears to be due to changes in the internal viscosity of red blood cells and can be eliminated in the most popular line of automated whole blood analyzers (Coulter Counters) by use of a simple correction table. Fresh blood obtained from volunteers was separated by centrifugation into fractions of increasing mean corpuscular hemoglobin concentration. A correction table for hematocrit values obtained by automated equipment was derived from the linear relationship between the discrepancy in hematocrit values and the manually obtained values for mean corpuscular hemoglobin concentration. With the use of the correction table, an average of three randomly selected fresh blood samples is sufficient to transfer a centrifugally determined hematocrit value to a multichannel analyzer with a coefficient of variation of 1.5%. Thus, this straightforward approach permits the microhematocrit to function as a practical calibration standard.