Polymorphonuclear leucocyte function tests: a comparison of cytochrome C reduction and flow cytometric analysis

Assay results were compared between the cytochrome C reduction test and flow cytometry using fluorescent beads or DCFH-DA (2', 7'-dichlorofluorescein diacetate) granules, in examining the phagocytosing and killing properties of polymorphonuclear leucocytes (PMN). When PMN samples from 20 healthy persons were assayed, no correlation was found between the cytochrome test and the phagocytosis (fluorescent beads) test or phagocytosing-killing (DCFH-DA) test by flow cytometry techniques. It is suggested that this might be caused by the fact that for technical reasons the two tests employed different stimulants and different substances to be phagocytosed. The simple flow cytometry procedure is now in widespread use as a PMN function test rather than the cytochrome C or nitroblue tetrazolium (NBT) dye reduction tests, and caution should be exercised in comparing and interpreting test results reported from separate laboratories. Because results using these two tests do not necessarily agree with each other, it seems preferable for PMN function testing to employ a combination of two or more approaches relying on different assay principles.