Diagnosis of Brucellosis Blood, bone marrow, and cerebrospinal fluid (CSF) cultures Acute and convalescent serologic testing (not reliable for B canis) and polymerase chain reaction (PCR) assay Blood cultures should be obtained; growth may take > 7 days, and subcultures using special media may need to be held for up to 3 to 4 weeks, so the laboratory should be notified of the suspicion of brucellosis.