A 69-year-old Caucasian man presented with general malaise and multiple febrile episodes that started several weeks prior to presentation. He was found to have a serum Cr of 3.6 mg/dl. Urinalysis showed 20 to 30 red blood cells/high-power field and occasional white blood cells. Urine showed a protein: Cr ratio of 2. A biopsy was performed to evaluate the etiology of the renal failure. Photomicrographs A and B show caseating necrosis in the renal parenchyma. Rare acid-fast bacilli were identified on the auramine-rhodamine (C) and acid-fast (D) stains. Follow-up laboratories confirmed the presence of a mycobacterium tuberculosis infection. Tuberculosis may involve the kidney as a localized process or a component of the disseminated disease. The presence of microorganisms on biopsy can be evaluated by using the Ziehl–Neelsen stain, also known as the acid-fast stain. The auramine-rhodamine stain is also used to visualize acid-fast bacilli by fluorescence microscopy. In this stain, the organisms fluoresce reddish-yellow. Although auramine-rhodamine has a lower specificity for acid-fast organisms compared with the Ziehl-Neelsen stain, it is far more sensitive and is, therefore, is often utilized as a screening tool in laboratories with fluorescence microscopy available.
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