[COMPARISON OF QuantiFERON® TB GOLD TEST RESULTS BEFORE AND AFTER ENDOTOXIN CONTAMINATION]

In response to a case of endotoxin contamination of tubes used in QuantiFERON® TB Gold (QFT-3G) testing in Japan in 2013, the effect of this contamination on QFT-3G test results was investigated.

We analyzed QFT-3G results from 4,258 participants in a tuberculosis contact investigation in Yamagata, Japan from September 2010 to April 2015. Of these, 2,488 samples were collected before the endotoxin contamination, while 1,770 samples were collected after the contamination.

Negative control values in the group tested after the contamination were significantly lower than those in the group tested before the contamination (P < 0.0005). The proportion of positive controls that exceeded the calculated limit (10IU/ml) in the group tested after the contamination (87.8%) was lower than that in the group tested before the contamination (96.8%; P < 0.0005). The proportion of intermediate results in the group tested after the contamination (3.2%) was markedly lower than that in the group tested before the contamination (6.6%).

Differences in QFT-3G test results were found to be related to a difference in blood collection before or after endotoxin contamination of blood collection tubes. Values resulting from QFT-3G testing were lower in blood samples that were collected after the contamination relative to those collected before the contamination.