Discussion

Abstract

McNulty: I would like to make a series of comments about the biopsy urease test and the factors that alter the sensitivity and specificity of the test. First, transport of the biopsy specimen is important. If you transport the specimen in a saline or other transport media, urease will obviously diffuse in the fluid, and will decrease the urease concentration in the biopsy specimen. Secondly, the volume of broth used, is important. If you use 1 ml broth, you will get more false negatives than if you use 0.5 ml. Thirdly, you must crush or squash the biopsy specimen well in the broth. We now have modified our broth: we have removed peptone and glucose from it, and this may prevent the false positives that other workers describe. We have also increased the percentage of phenol red indicator, and our modified broth now has four times the amount of phenol red as in the method described by Deltenre. Lastly, the pH of the broth is extremely important; our pH is 6.8. If you use a lower pH, the phenol red indicator will obviously take longer to change colour. Using this modification, we have now analysed 600 biopsy specimens, achieving a specificity of 99.7% and a sensitivity of 96%. Also 72% of positive tests are positive within 2 h. If all researchers used the same biopsy urease broth, everybody would achieve this specificity and sensitivity.