To the Editor.
—In the February Archives (1983;143:282-283) Fischer and Fischer claim that the mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) provide little clinical information and should be abandoned. However, laboratories still use these indices as quality control indicators to detect instrument malfunction.The average value of mean corpuscular volume (MCV), MCH, and MCHC for a large number of patients remains relatively constant in each laboratory. Modern hematology instruments incorporate microcomputers that use a special "moving average" formula to monitor patient RBC indices. The moving average values for MCV, MCH, and MCHC can rapidly detect instrument malfunction and indicate which RBC parameters are at fault.1In addition, laboratory technologists use the consistency of the MCHC (hemoglobin/RBC × MCV) to ensure accuracy of the measured RBC parameters on individual patient samples. An abnormal MCHC value must be regarded with suspicion. Elevated MCHC values are seen with spherocytosis,