An improved micromethod for evaluating the phagocytic potential of granulocytes by the nitroblue tetrazolium (NBT) slide test.

A comparison of granulocyte preparations obtained with the original endotoxin-stimulated nitroblue tetrazolium (NBT) slide test and a modified NBT slide test developed in our laboratory was performed as blind study on paired peripheral blood samples from 25 normal, adult humans and 25 normal, adult BALB/c mice. Distinct qualitative differences between granulocyte preparations obtained with the two NBT methods were observed. The original NBT procedure yielded cell preparations which were poorly stained and morphologically altered. In contrast the modified procedure consistently resulted in human and murine cell preparations which were intensely stained and morphologically intact. A blinded comparison of the number of NBT-positive cells showed quantitative differences between the original and modified NBT slide tests. The average percentage of NBT-positive cells of the 25 normal human subjects was 79.81 +/- 17.40 with the original method and 90.83 +/- 7.71 with the modified method (p less than 0.0002). The average percentage of NBT-positive cells obtained on 25 normal BALB/c mice was 29.52 +/- 17.26 and 69.22 +/- 9.01 for the original and modified procedures, respectively (p less than 0.0001). The increased numbers of NBT-positive cells observed with the modified NBT procedure may have resulted from variation in the original method due to the misinterpretation of weakly stained and morphologically altered granulocyte preparations.