Accuracy of low platelet counts on the Coulter S-Plus IV

Recent improvements have occurred in the flagging criteria for erroneous platelet counts on Coulter S-Plus series instruments. The authors tested the accuracy of the S-Plus IV on over 400 patient samples with low platelet counts (less than 50,000/microL) as compared with phase microscopy. Only a small number of samples gave discrepant results (difference greater than 10,000/microL), and, when investigated, most often were found to be due to erratic phase microscopy results. Approximately one-third of all low platelet counts in our laboratory were flagged ("error code 10") by the instrument and required determination by phase microscopy. In addition, to prevent erroneous results due to giant platelets or microcytic red blood cells, the platelet histogram should be inspected for return to baseline at 20 cubic micrometers (fL).