Precision and accuracy in the measurement of the cholesterol saturation index of duodenal bile. Lack of variation due to the menstrual cycle.

The reproducibility of measurement of the cholesterol saturation index of duodenal bile has been investigated in 5 healthy male and 10 healthy female volunteers. Two possible causes for variation in the saturation index were examined. First, the precision of the assays for cholesterol, bile acids, and phospholipids was such that after replicate analysis of eight individual bile samples, analytic variation produced cholesterol saturation index values which covered a mean range of 0.09 +/- 0.01 (SEM). Secondly, biologic variation was observed in all volunteers when eight duodenal bile samples were collected on different days over a 1-month period. Biologic plus analytic variation accounted for large fluctuations in the biliary cholesterol saturation index, covering a mean range of 0.32 +/- 0.05 (SEM). The magnitude of both types of variation was the same for men and women and was not related to physiologic changes in sex hormone levels during the menstrual cycle. After allowing for analytic variation, the cholesterol saturation index of duodenal bile accurately reflected that of gallbladder bile when collected at the same time from gallstone patients at operation.