Can stone composition be predicted by plain X-ray and/or non-contrast CT? A study validated by X-ray diffraction analysis

Abstract
Background
The stone composition has a great influence on the outcome of its treatment. There are several tests to predict the composition of stones preoperatively and stone analysis postoperatively. Herein, we want to evaluate if the stone composition could be predicted from plain X-ray KUB (PKUB) and/or non-contrast CT (NCCT) validated by in vitro X-ray powder diffraction analysis (XRD).

Methods
Between April 2014 and March 2016, 100 cases with urinary tract stones were included in the study. The radio-opacity of the stones in PKUB, stone density by NCCT, and after stone extraction, XRD were performed. Statistical analysis for the results was performed using Chi-square and Fisher exact tests for categorical variables and Mann–Whitney U and Kruskal–Wallis H for the nonparametric variables. The receiver operating characteristic curve was constructed to determine the best cutoff value.

Results
This study included 74 males and 26 females with a median age of 32 years (range 2–70). Regarding the radio-opacity by PKUB, there were 30 stones dense opaque, 44 opaque, 21 faint opaque, and 5 radiolucent. XRD revealed 97 mixed and 3 pure stones. The calcium oxalate monohydrate (COM) stone composition could be predicted in dense opaque stone by PKUB in 75.9% and urate composition in the radiolucent stone by 40%. The cutoff value of HU density by NCCT to the dense opaque stones in the PKUB was > 1020 and for radiolucent stones was < 590.

Conclusion
Stone radio-opacity by PKUB and its attenuation value by NCCT could successfully predict its calcium oxalate monohydrate, struvite, and urate composition. However, the chemical stone analysis is still required as most stones are mixed.