The diagnostic usefulness of bone marrow cultures in patients with fever of unknown origin.

Bone marrow cultures (BMCs) and blood cultures (BCs) are frequently obtained in the evaluation of fever of unknown origin (FUO). However, the low yield of clinically significant isolates leads to questions about their cost-effectiveness. We retrospectively compared BMC with BC and studied the usefulness of bone marrow trephine biopsy (BMTB) histopathology in detecting infection in an unselected population of 61 patients with FUO, among whom 215 BMCs had been performed. For patients who had undergone BMTB, the histopathology was evaluated for granulomas and microorganisms. Only 1 BMC had a clinically significant isolate, Mycobacterium avium complex (MAC), which was also identified by BC. Rhodotorula rubra was found in the BMC of another patient and classified as a contaminant. Both patients had HIV infection. No growth occurred in BCs for the other 59 patients. Culture results for all 26 BMTB specimens were negative; 4 contained nonnecrotizing granulomas, including the case with MAC. BMCs are probably not justified for routine initial evaluation of FUO, but may be valuable after culture results for blood and easily obtainable tissues have been negative. Bone marrow histopathology and special stains for microorganisms in the absence of granulomas were noncontributory.