The estimation of phospholipids in bile.

Total and lipid phosphorus were measured in the duodenal aspirate of 24 fasting subjects following an injection of cholecystokinin. The lipid phosphorus values were lower than the total phosphorus, a difference most pronounced in dilute samples. Storage at -20 degrees C over 4 weeks resulted in a loss of over 50% lipid phosphorus. Such alterations in the lipid phosphorus affected the calculation of biliary phospholipid and hence the saturation index of cholesterol in bile causing it to be erroneously elevated. It is concluded that analysis of bile samples should be undertaken on freshly obtained samples and include a preliminary step for the extraction of lipids.