Biochemical composition of urolithiasis from stone dust - a matched-pair analysis

To determine if the biochemical composition of a renal calculus can be measured from 'dust' obtained during laser fragmentation.

This pilot study was set in a tertiary referral hospital between 2011 and 2013. Stone dust was aspirated through the ureteroscope during lasering and a stone fragment also retrieved. Both samples were analysed by Fourier transform infrared spectroscopy. Pairs of stone (standard) and dust were compared. They were deemed to match if both were of the same pure biochemical composition or if the predominant constituent was the same in mixed compositions, as this would not alter subsequent management.

Paired specimens were obtained from 97 ureteroscopies. The dust specimen was sufficient for analysis in 66/97 (68%) cases. Of these, the composition matched that of the stone in 49/66 (74%) cases. In 12/66 (18%) the biochemistry differed only in the relative proportions of each constituent, whilst 5/66 (8%) showed a complete mismatch. The overall sensitivity was 51% and specificity 97%. A limitation of the study is the small number of some stone types analysed (<5 each cystine, atazanavir, mixed uric acid/calcium oxalate).

We have demonstrated in this pilot study successful proof of principle. Further work is required initially to improve the number of sufficient dust specimens. This technique may offer an option when a stone cannot be retrieved ureteroscopically.