Nitroblue tetrazolium: its use in the diagnosis of infection and in the study of leukocytes, lipoproteins and liposomes
A rapid, objective indicator of pyogemc infection would be of great value in the practice of clinical medicine. On the basis of earlier studies it was claimed that the nitroblue tetrazolium ( NBT) test might fulfill such a role. In view of the potential value of this test, it was reassessed m order to determine its diagnostic accuracy and clinical value. The results obtained in this study did not conform with those previously published. Elevated NBT scores were not diagnostic of pyogenic infection, there was a wide overlap of the results of tests performed on patients with pyogenic disease, patients with other diseases and normal subjects. In addition, there was a significant observer error in the interpretation of the slide preparations. The extent of this error was reduced with experience, but was still considerable in the hands of experienced observers. In the NBT test, the dye enters neutrophils by phagocytosis of NBT in particulate form, complexed to heparin and/or '·fibrinogen. The proportion of neutrophils which phagocytose these complexes seems to be related to the severity of illness of the patient. As serum from these patients is capable of enhancing phagocytosis of complexed dye by normal cells, a humeral factor could be responsible for the increased phagocytosis of complexed NBT indicated by a positive test. , Of the compounds tested, man m vitro model system designed to simulate the NBT test, 3 a,l_acid glycoprotein, immunoglobulins and endotoxin, in concentrations that occur in vivo, enhanced NBT reduction. Any one of these compounds, singly or in combination, could be responsible for positive NBT tests.
Infection, diagnosis, communicable diseases
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Centre for Infectious Disease Epidemiology and Research