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Introduction: There has been a shift in the stone composition of large renal calculi from predominantly infectious to metabolic. Post-operative infectious complications remain of primary concern with PCNL, especially in the setting of infectious stones. It is difficult to identify whether a stone is infectious, as routine urine cultures are often not predictive. We sought to identify differences in metabolic and infectious stones treated with PCNL using the S.T.O.N.E Nephrolithometry score.
Methods: We retrospectively reviewed patients who underwent PCNL at 3 academic institutions between 2002 and 2014. Stone composition, stone characteristics, patient factors and the S.T.O.N.E Nephrolithometry score were reviewed. Comparisons were made between infectious and metabolic stone groups using Fisher’s exact tests and Wilcoxon rank sum tests.
Results: 192 kidneys underwent PCNL. 144(75%) were metabolic and 48(25%) were infectious. Of the metabolic stones, 51%(73) were calcium phosphate. Infection stones were 63% female and metabolic stones were 46% female. Infectious stones were found to have a significantly higher S.T.O.N.E nephrolithometry score than the metabolic group(mean 9.2 vs. 8.1, p<0.001). The components driving the difference were stone volume(1234 vs. 544, p<0.001) and number of calyces involved(2.6 vs. 2.2, p<0.02). Infectious stones had significantly lower average Hounsfield units (765 vs. 899, p<0.05).
Conclusions: The S.T.O.N.E Nephrolithometry score is a useful tool to help identify infectious based renal calculi in the pre-operative setting. This knowledge can assist patient counseling and pre-operative planning. It also may help identify patients that need longer courses of pre-procedure antibiotics.