[Analysis of the statistical value of various commercially available stool tests - a comparison of one stool sample...

Guajac based fecal occult blood tests have proven to reduce mortality of colorectal cancer - despite their unsatisfactory statistical values. The potential of newer tests is yet inconclusive. We compared two guajac based, four immunochemical and the M2-PK test with colonoscopic and histological results as a reference.

In 1128 stool samples of patients undergoing (screening) colonoscopy the mentioned tests were performed.

Positivity rate was 1.9 to 4.1 % for guajac based and immunochemical tests, M2-PK reached 11.6 %. In case of advanced neoplasias, no significant differences in sensitivity (7.3 - 20 %), specifity (96.6 - 98.4 %), positive predictive value (16.7 - 30.6 %) or accuracy (92.9 - 94.0 %) between guajac based and immunochemical tests were encountered. The slightly higher sensitivity of M2-PK (27.3 %) did not reach statistical significance - however the comparatively low specifity (89.2 %) and accuracy (86.2 %) were clearly lower compared to all other tests. Regarding all neoplasia, immunochemical tests performed better than conventional hemoccult, but the difference did not reach statistical significance. In this group, the sensitivity of M2-PK is clearly better, but specifity is clearly inferior to all other tests.

Low sensitivity and low predictive values are explained by the study design with single test and low prevalence of neoplasia. Due to small numbers, there is only a trend, but no significant difference between the performance of conventional hemoccult compared with immunochemical and high senstitive guajac tests. Because of its low specificity, M2-PK is not an appropriate screening test for colorectal neoplasia.