Serological assay by use of glycopeptidolipid core antigen for Mycobacterium avium complex

We evaluated the clinical usefulness of glycopeptidolipid (GPL) core antigen for diagnosing Mycobacterium avium complex (MAC) pulmonary disease (MAC-PD), including patients with clinically suspected MAC-PD.

GPL core antibody levels were measured in 57 patients with MAC-PD satisfying the American Thoracic Society (ATS) criteria for pulmonary disease due to non-tuberculous mycobacteria (NTM), and in 18 patients with clinically suspected MAC-PD, 10 with MAC contamination, 18 with pulmonary tuberculosis (TB), 9 with other NTM disease, 18 with other lung diseases, and 20 healthy subjects.

The positive response rate was 77% for MAC-PD, 39% for suspected MAC-PD, 10% for MAC contamination, and 0% for pulmonary TB, other NTM diseases, other lung diseases, and healthy subjects. GPL core antibody levels were significantly higher in patients with MAC-PD than in those of the other groups (p < 0.01). The sensitivity and specificity of the GPL core antibody assay for MAC were 77% and 99%, respectively. Among 13 patients with MAC-PD who showed false-negative results, 5 had immunosuppressive underlying diseases. No significant correlations between the antibody level and species of MAC, clinical disease types, and extent of the disease on chest computed tomography were found in patients with MAC-PD.

This enzyme immunoassay kit is a useful supportive method for the rapid and convenient diagnosis of MAC-PD using a small dose of serum, and for the differentiation of MAC-PD from other lung diseases. However, underlying diseases need to be considered in the interpretation of negative results.