An historical review of quality control in hematology.

As the use of laboratory techniques in diagnostic medicine increase, it became obvious that standardized reference methods and stable controls were essential in order for results obtained in different laboratories to be comparable. Certain procedures and standards have been adopted to provide QC in hematology. Currently procedures include the following: cyanmethemoglobin for HGB determinations; particle counter for RBC and WBC counts; phase microscopy for PLT counts; and packed cell volume for HCT determinations. These serve as acceptable reference methods for multichannel hematology instruments. Instruments that are used must be carefully calibrated. Calibration of the spectrophotometer should be performed using an acceptable standard for hemoglobin. Calibration of the particle counter to determine RBC and WBC counts should be performed using a fresh sample of anticoagulated (EDTA) blood. PLT counting by phase hemacytometry should be used to obtain reference values for automated PLT counters. Centrifuges that are used to obtain microhematocrit values should be calibrated for maximum packing times and times checked against an electric clock. After the instruments have been calibrated, fresh whole blood is measured to determine a target value for each determination. Primary calibration of multichannel instruments is performed by calibrating each parameter to the target value. This is performed initially and then once each week. Two techniques that are commonly used to monitor instrument performance are: 1) the use of at least two levels of commercially prepared control samples to prepare either Levey-Jennings charts or the simple Cusum charts, which detect presymptomatic instrument problems; and/or 2) the use of 500-1,000 patient indices and mean WBC counts analyzed by the XB statistic to establish limits for monitoring instrument performance.