Identification of Patients with Cholesterol or Pigment Gallstones by Discriminant Analysis of Radiographic Features

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Abstract
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.)