MISDIAGNOSIS OF MULTIDRUG-RESISTANT TUBERCULOSIS POSSIBLY DUE TO LABORATORY-RELATED ERRORS

Objective.-To describe 9 cases where a misdiagnosis of multidrug-resis tant tuberculosis (MDR TB) was made, possibly due to laboratory-relate d errors. Design.-Case series. Setting.-Public and private hospitals, outpatient clinics, and mycobacteriology laboratories serving those in stitutions in Los Angeles County, Calif. Patients.-Consecutive sample of 70 patients diagnosed with MDR TB who were identified between Augus t 1993 and August 1994 by the Multidrug-Resistant Unit within TB Contr ol in Los Angeles County. Outcome Measure.-Detection of laboratory-rel ated diagnostic errors. Results.-Pulmonary MDR TB was misdiagnosed in 9 (13%) of 70 patients. Reasons why the diagnoses appeared to be erron eous are as follows. growth of MDR TB from an old tuberculous lesion i n a patient who was never treated for TB and whose diagnosis predated anti-TB drugs (1 case), documented contamination with Mycobacterium av ium complex (1 case), suspected cross-contamination (1 case), suspecte d specimen mislabeling (1 case), successful treatment using drugs to w hich the isolate was reportedly resistant (4 cases), discrepant suscep tibility test results on additional sputum specimens submitted by the patient (2 cases), and no clinical evidence of TB (3 cases). Conclusio ns.-These cases emphasize the diagnostic errors that can occur if myco bacterial susceptibility results are not correlated with all clinical data including other laboratory results for a given patient. We conclu de that susceptibility results alone are not enough to dictate treatme nt, and that careful clinical correlation is necessary in making the d iagnosis of MDR TB.