[Diverging detection limits of immunochemical tests for occult blood underline the necessity of standardization and...

Immunological fecal occult blood tests (FIT) are superior in detecting colorectal cancer and its precursors compared to conventional Guajac-based tests. Besides quantitative, laboratory-based FITs qualitative, office-based FITs are increasingly employed. Studies have shown major variation of these tests with respect to sensitivity and specificity, which is most probably caused by different detection limits. In the present study we therefore determined and compared the detection limits and other criteria of commercial FITs.

We determined the detection limits for 21 qualitative and one quantitative FIT using commercial control solutions with defined hemoglobin (Hb) concentrations. These detection limits were compared with the manufacturers' data.

The detection limits of the tests showed a wide range of 2 to over 60 µg Hb per gram stool. In many cases the detection limits we determined were not in accordance with the manufacturers' data. Two tests didn't show a positive reaction even with the highest hemoglobin concentration of 440 ng/mL. On the other hand one test showed a positive reaction even at the lowest hemoglobin concentration of 25 ng/mL.

The large differences in the detection limits found in this study are consistent with observations of large variation of sensitivity and specificity of qualitative FITs in screening practice. Proper clinical validation of each FIT is to be required before admission for colorectal cancer screening. An additional regular quality control, i. e. by means of external quality control measures and documentation of results of colonoscopies following positive tests results, should be mandatory.