Hemac is an automated blood counting system which is based on production of impulses from light scattered and diffracted by cells flowing past a laser beam. The pulses are processed electronically for cell counts and packed cell volume; haemoblobin is measured as cyanmethaemoglobin; absolute values are computed. On evaluation the precision was of the order of 2% for Hb and RBC, 2-8% for PVC, and 3% for WBC. When compared with other methods in the routine laboratory, PCV and absolute values gave divergent results, but PCV was found to correlate well with microhaematocrit corrected for trapped plasma. This suggests that Hemac may more closely reflect true values of PCV, MCV, and MCHC than other routine methods. Whether this "accuracy" is necessarily an advantage must be considered ietation of the blood count data, especially MCV, are discussed.
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