POLARIZING MICROSCOPY OF PARTIALLY DISSOLVED GALLSTONE POWDER - A SIMPLE TECHNIQUE FOR STUDYING GALLSTONE COMPOSITION

A quick and reliable method for estimating the proportion of constitue nts of a stone may be useful in determining the prevalence of chemical type of gallstones in different geographic areas or ethnic groups. Ch emical and infrared spectroscopy estimation facilities are not commonl y available in many parts of the world and visual inspection may not b e reliable for scientific purposes. To investigate whether identificat ion of microcrystalline solids in partially dissolved stone powder cou ld accurately predict the chemical nature of the gallstone we undertoo k a blind study on 40 samples of gallstones and compared our results w ith those of visual inspection and quantitative infrared spectroscopy. There were 29 cholesterol stones (mean cholesterol 83.4 +/- 7.5%), si x intermediate cholesterol stones (mean cholesterol 48.0 +/- 21.2%) an d five pigment stones (mean cholesterol 14.3 +/- 4.3%) as determined b y quantitative infrared spectroscopy. Microscopic examination of parti ally dissolved gallstone powder in ethanol correctly identified all 29 cholesterol gallstones (sensitivity 100%, specificity 92%), four of s ix intermediate cholesterol stones (sensitivity 67%, specificity 100%) and all five pigment stones (sensitivity 100%, specificity 97%). It a lso detected microspheroliths of calcium carbonate in 14 of 16 calcium carbonate containing gallstones (sensitivity 88%, specificity 100%). The chemical grouping of stones on the basis of microscopic examinatio n was correct in 37 (93%) of 40 samples and was especially useful in i dentifying 'intermediate' cholesterol stones which cannot be recognize d by visual inspection. Thus microscopic examination of powdered galls tones appears to be a simple and reliable method of determining gallst one composition.