A clinical trial of three-part electronic differential white blood cell counts.

Three-part white blood cell differential counts (diffs), performed during electrical impedance counting of blood cells, can accurately classify lymphocytes, granulocytes, and mononuclear cells in 85% of specimens, with an error rate not exceeding that of conventional diffs. To assess the clinical utility of the new test, we tried it for three months on a medical unit. Conventional diffs were no better than three-part diffs or total white blood cell counts in signaling clinical changes, and the same decisions would have been made in 78% of instances if only three-part diffs were available. The three-part diff is as reliable a clinical index for monitoring most inpatients as the conventional diff or white blood cell count. Although its use could effect significant cost savings, acceptance of the new test seems unlikely unless enforced by administrative flat.