Optimal conditions for the NBT-reduction test have been sought. Increasing heparin concentrations up to 100 units per ml and a delay in performance of the test, especially when blood specimens are kept at room temperature, resulted in higher values for the NBT index, which then sometimes exceeded the upper limit of normal in healthy people and in uninfected patients. The effect of H, composition of the buffer, and dye concentration was also investigated. Phosphate-buffered saline H 7·2 containing 0·1% NBT dye, without glucose, gave the most reliable results.

In endotoxin-stimulated NBT tests, the following procedure is recommended: incubation of 0·1 ml whole blood with lyophilised endotoxin 20 μg per ml, for 15 min. in a 37°C water bath, followed by the standard test with a 0·2% NBT solution. By this technique, the leucocyte reaction to various types of lipopolysaccharides was of the same order of magnitude. Drug therapy having an effect on blood components lowered this reaction, whatever the source of endotoxin used as stimulant.

The importance of NBT-reduction tests is discussed. Standard conditions of test performance are strictly requisite if comparable results are to be obtained and if data not corresponding with the apparent clinical and other laboratory findings are to be evaluated correctly. The stimulated NBT test, performed in parallel with the standard test, is useful in the interpretation of abnormal results and in the detection of factors with a temporary or permanent effect on the phagocytic activity of PMN leucocytes.


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