Bile salts encompass salts derived from four distinct types of bile acids: cholic, deoxycholic, chenodeoxycholic, and lithocholic. These bile acids form intricate salts or acids by binding with either glycine or taurine. Originating from the bile, these bile salts make their way into the small intestine, where they serve as detergents. Their primary function is to emulsify fat, thereby reducing the surface tension on fat droplets. This reduction in tension enables enzymes, specifically lipases, to effectively break down the fat. Subsequently, in the terminal ileum, bile salts are absorbed and enter the bloodstream. Once in the blood, they are taken up by the liver and subsequently re-excreted in bile, participating in the enterohepatic circulation.
In instances of obstructive jaundice, both bile salts and bilirubin can be identified in urine. In this condition, increased intrabiliary pressure causes the regurgitation of bile salts and conjugated bilirubin into the bloodstream from biliary canaliculi. The subsequent excretion of these elements in urine is detectable through a test known as the Hay’s surface tension test. This examination capitalizes on the ability of bile salts to lower surface tension.
To conduct the Hay’s surface tension test, collect a sample of fresh urine in a conical glass tube at room temperature. Sprinkle sulphur particles onto the urine's surface. If bile salts are present, the sulphur particles will sink to the bottom due to the surface tension-lowering effect of bile salts. Conversely, if the sulphur particles remain on the surface, it indicates the absence of bile salts. Notably, the presence of thymol, a preservative, can yield false positive results in this test.