Polarizing microscopy of partially dissolved gallstone powder: a simple technique for studying gallstone composition.

A quick and reliable method for estimating the proportion of constituents of a stone may be useful in determining the prevalence of chemical type of gallstones in different geographic areas or ethnic groups. Chemical and infrared spectroscopy estimation facilities are not commonly available in many parts of the world and visual inspection may not be reliable for scientific purposes. To investigate whether identification of microcrystalline solids in partially dissolved stone powder could accurately predict the chemical nature of the gallstone we undertook a blind study on 40 samples of gallstones and compared our results with those of visual inspection and quantitative infrared spectroscopy. There were 29 cholesterol stones (mean cholesterol 83.4 +/- 7.5%), six intermediate cholesterol stones (mean cholesterol 48.0 +/- 21.2%) and five pigment stones (mean cholesterol 14.3 +/- 4.3%) as determined by quantitative infrared spectroscopy. Microscopic examination of partially dissolved gallstone powder in ethanol correctly identified all 29 cholesterol gallstones (sensitivity 100%, specificity 92%), four of six intermediate cholesterol stones (sensitivity 67%, specificity 100%) and all five pigment stones (sensitivity 100%, specificity 97%). It also 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 examination was correct in 37 (93%) of 40 samples and was especially useful in identifying 'intermediate' cholesterol stones which cannot be recognized by visual inspection. Thus microscopic examination of powdered gallstones appears to be a simple and reliable method of determining gallstone composition.