[Misdiagnosis of urinalysis due to in vivo formation of urinary stones].

The occurrence of biochemically unaltered urinalyses in patients with severe recurrent stone formation is not a rare observation in practice. The possible reasons for that phenomenon are manifold. We show that stone growth-related urinary depletion of lithogenic constituents caused by acute growth of urinary calculi in vivo can be an important reason for the observed phenomenon. The described process which can strongly influence the urinary composition occurs in any stone-bearing patient. Thus, it is strongly recommended that stone-related alterations be taken into account when interpreting the urinalyses of these patients. Based on simplified model assumptions, the extent of the expected chemical depletion effect can be calculated for any stone patient's urine sample. In two easy-to-use nomograms, we have combined the key parameters which govern the process, allowing the user a fast and easy estimation.