Serodiagnosis of Mycobacterium avium-complex pulmonary disease using an enzyme immunoassay kit

Rationale The diagnosis of Mycobacterium avium-complex pulmonary disease (MAC-PD) and/or its discrimination from pulmonary tuberculosis (TB) is sometimes complicated and time consuming. Objectives: We investigated in a six-institution multicenter study whether a serologic test based on an enzyme immunoassay (EIA) kit was useful for diagnosing MAC-PD and for distinguishing it from other lung diseases. Methods: An EIA kit detecting serum IgA antibody to glycopeptido-lipid core antigen specific for MAC was developed. Antibody levels were measured in sera from 70 patients with MAC-PD, 18 with MAC contamination, 37 with pulmonary TB, 45 with other lung diseases, and 76 healthy subjects. Measurements and Main Results: Significantly higher serum IgA antibody levels were detected in patients with MAC-PD than in the other groups (P < 0.0001). Setting the cutoff point at 0.7 U/ml resulted in a sensitivity and specificity of the kit for diagnosing MAC-PD of 843 and 100%, respectively. Significantly higher antibody levels were also found in patients with nodular-bronchiectatic disease compared with fibrocavitary disease in MAC-PD (P < 0.05). There was a positive correlation between the extent of disease on chest computed tomography scans and the levels of antibody (r = 0.43, P < 0.05) in patients with MAC-PD. Conclusions: The EIA kit is useful for the rapid diagnosis of MAC-PD and for differentiating MAC-PD from pulmonary TB and, if validated by studies in other populations, could find wide application in clinical practice.