Inaccurate Reporting of Mineral Composition by Commercial Stone Analysis Laboratories: Implications for Infection and Metabolic Stones

Purpose: We determined the accuracy of stone composition analysis at commercial laboratories. Materials and Methods: A total of 25 human renal stones with infrared spectroscopy determined composition were fragmented into aliquots and studied with micro computerized tomography to ensure fragment similarity. Representative fragments of each stone were submitted to 5 commercial stone laboratories for blinded analysis. Results: All laboratories agreed on the composition of 6 pure stones. Only 2 of 4 stones (50%) known to contain struvite were identified as struvite at all laboratories. Struvite was reported as a component by some laboratories for 4 stones previously determined not to contain struvite. Overall there was disagreement regarding struvite in 6 stones (24%). For 9 calcium oxalate stones all laboratories reported some mixture of calcium oxalate but the quantity of subtypes differed significantly among laboratories. In 6 apatite containing stones apatite was missed by the laboratories in 20% of samples. None of the laboratories identified atazanavir in a stone containing that antiviral drug. One laboratory reported protein in every sample while all others reported it in only 1. Nomenclature for apatite differed among laboratories with 1 reporting apatite as carbonate apatite and never hydroxyapatite, another never reporting carbonate apatite and always reporting hydroxyapatite, and a third reporting carbonate apatite as apatite with calcium carbonate. Conclusions: Commercial laboratories reliably recognize pure calculi. However, variability in the reporting of mixed calculi suggests a problem with the accuracy of stone analysis results. There is also a lack of standard nomenclature used by laboratories.