In a search for a way to distinguish cholesterol gallstones from pigment gallstones by oral cholecystography, we evaluated 56 patients with surgically confirmed cholelithiasis. Only buoyancy was highly predictive of gallstone composition: all 14 patients with floating stones had cholesterol stones (P<0.01), but only one third of the patients with cholesterol stones had stone buoyancy. Using a function derived by stepwise discriminant analysis, we separated patients with cholesterol stones from those with pigment stones. The predictive accuracy was significantly improved: sensitivity was 95 per cent (37 of 39 patients with cholesterol stones), specificity was 82 per cent (14 of 17 patients with pigment stones), and efficiency was 91 per cent (51 of 56 total patients). The resultant function, applied prospectively to 17 additional cases, classified all of them correctly. In patients with cholelithiasis and gallbladders visualized on oral cholecystography, discriminant analysis can improve the prediction of gallstone composition and the subsequent selection of medical or surgical therapy. (N Engl J Med. 1981; 304:808–11.) ALTHOUGH dissolution of cholesterol gallstones has been undertaken during the past decade, 1 2 3 noninvasive differentiation of these stones from pigment stones has not been highly reliable. Current criteria for the selection of patients for medical treatment of cholelithiasis include the demonstration of a functioning gallbladder with oral cholecystography and the presence of either entirely radiolucent gallstones or lucent gallstones with a calcified center less than 3 mm in diameter.3 4 5 Reliability in predicting stone composition is important, since dissolution takes between one and two years and entails a large expenditure of money and time. Trotman et al. have reported that 14 per. . .
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