Rapid Serological Detection of Anti-GM-CSF Autoantibodies in Autoimmune Pulmonary Alveolar Proteinosis Using a Novel Immunochromatographic Test.

Background and objectivesAnti-GM-CSF autoantibodies (GMAbs) are essential biomarkers for diagnosing autoimmune pulmonary alveolar proteinosis (APAP). While enzyme-linked immunosorbent assay (ELISA) is commonly used, it is time-consuming and requires specialised equipment. We developed a novel immunochromatographic test (ICT) for rapid detection of GMAbs in clinical settings.MethodsICT was designed using a gold colloid aggregation method. The test line intensity was calibrated to be close to the ELISA cutoff of 1.65 U/mL using polyclonal anti-GM-CSF antibodies purified from the pooled patient sera. Validation was performed in 211 APAP and 171 non-APAP cases. The sensitivity, specificity, and correlation with ELISA were assessed.ResultsUsing known concentrations of serum from APAP patients, the grey zone concentration, which was difficult to judge by visual inspection, was found to be below 3.5 U/mL. In serological diagnosis of 211 cases with APAP and 171 cases with non-APAP lung diseases, the sensitivity and specificity by five examiners were 100% and 98.8%, respectively. When the GMAbs positive serum was serially diluted, the end point dilution titre showed a strong correlation overall (ρ = 0.93) with the antibody concentration determined by the conventional ELISA method, but the correlation was weaker in the low concentration range below 60 U/mL (ρ = 0.67), suggesting that the accuracy of ICT was reduced in the lower concentration range.ConclusionThis ICT offers a practical alternative to ELISA for APAP serological diagnosis. It enables rapid testing in clinical settings and supports the implementation of GM-CSF inhalation therapy.