Evaluation of the phagocytic-bactericidal capacity of neutrophils: A current review

Abstract

The evaluation of neutrophil function is an important consideration in the overall ability of the host defense system to cope adequately with an active infection. Although knowledge of interaction between white blood cells and bacteria and the subsequent changes in intracellular metabolism has increased rapidly within the past several years, the precise mechanisms involved and their relative importance have yet to be elucidated unequivocally. This lack of understanding is largely responsible for the difficulty in establishing a reliable laboratory test of neutrophil phagocytic-bactericidal capacity. The most widely used method for evaluating neutrophil function is the nitro blue tetrazolium (NBT) test and its variations. The reduction of this dye is thought to be indicative of certain intracellular metabolic steps essential to bactericidal competency. Although useful in certain clinical situations, inherent weaknesses in the NBT test itself, as well as a number of complicating clinical variables, have detracted significantly from its reliability. The NBI and LBI, statistically based indices of neutrophil function, are inordinately dependent upon establishment of control values. Even though it is statistically superior to the NBI, the LBI is unduly complicated and probably is equally incapable of detecting slight changes in neutrophil function. The direct measurement tests, which are also in vitro assays, have the advantage of distinguishing phagocytic from intracellular processes. Interpretation of results, however, requires 36–48 hr bacterial colony counts. The sensitivity for other than gross alterations of leukocyte function remains to be established. Although obviously needed in the management of the increasingly complex patients being considered for operative care, these “first generation” indicators of leukocyte function have proved as deceptive as informative. Refinements of concept and technique will be needed before such evaluations contribute reliably to clinical patient care decisions.