Faecal fat and faecal weight: reproducibility and diagnostic efficiency of various regimens.

The reproducibility of measuring 3-day faecal fat and weight in outpatients, in inpatients served a fixed diet, and in intake-excretion studies was estimated from 64 duplicate measurements. Qualitatively, no significant difference between the results of the three regimens was found. Quantitatively, however, the more controlled the regimen, the better the reproducibility. The diagnostic efficiency of measuring faecal fat was estimated from comparison with the other clinical findings. No significant difference between the three regimes was found, the overall diagnostic efficiency being 83% (95% confidence limits, 71-91%). The inconvenience, the uncontrollable sources of error, and the difficulties in obtaining quantitative information still make measurement of faecal fat and weight inexpedient as a clinical test.