NEW YORK (Reuters Health) - HIV-infected patients with urinary lithiasis should undergo a complete metabolic evaluation, because more often than not, their renal stones are composed of calcium salts or uric acid rather than crystallized protease inhibitor.

Dr. Robert B Nadler and his colleagues at the Northwestern University Medical School in Chicago note in the February issue of the Journal of Urology that urinary stones in patients treated for HIV are thought to be composed mainly of protease inhibitor. However, they have seen "many" patients with non-PI stones, and so investigated further.

They describe 24 HIV-infected patients on protease inhibitors who developed nephrolithiasis. Stones were recovered from 18 patients.

Only 4 stones of 14 patients being treated with indinavir treatment were composed of indinavir. Six of the remaining stones were composed of calcium oxalate monohydrate and dihydrate, three were ammonium acid urate, four were uric acid and one was calcium phosphate.

The investigators found abnormalities such as hypocitraturia and hyperoxaluria in 8 of 10 patients examined by 24-hour urine collection.

Dr. Nadler's group recommends urine analyses that include 24-hour volume, levels of calcium, oxalate, uric acid, magnesium, phosphorous and sodium, as well as supersaturations. Measurements of serum levels of urea nitrogen, creatinine, calcium and electrolytes are also advised, with consideration of malnutrition, infectious diarrhea and bowel disease as potential contributors to the risk of urolithiasis.

By doing so, clinicians may avoid having to discontinue or switch antiretroviral therapy or perform unnecessary surgical measures, the authors note.

J Urol 2003;169:475-477.

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