We describe a rapid polymerase chain reaction (PCR)-based test for diagnosing Mycobacterium avium directly from blood specimens. Blood was collected in anticoagulant (EDTA) from patients who also had blood cultures performed by the lysis-centrifugation method. Blood samples were centrifuged on a Ficoll-Hypaque gradient to purify peripheral blood mononuclear cells. The purified cells were washed and incubated in the presence of Chelex-100 (a divalent cation-binding resin), boiled to release mycobacterial DNA, and then amplified with M. avium-specific PCR primers. Amplification was detected by hybridization with radiolabelled probe, and the results were compared with the culture results. The PCR assay gave positive results for 12 of 15 specimens that were taken from patients with positive cultures for M. avium complex (sensitivity, 80%). The three PCR-negative specimens in this group showed evidence of PCR inhibition. The PCR assay gave positive results for 32 of 228 specimens taken from patients with negative cultures (specificity, 86%). Of these 32 PCR-positive culture-negative specimens, 27 were also positive when amplified with primers specific for the genus Mycobacterium, suggesting that PCR may be more sensitive than culture
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