| Summary: | Background and objectives: Commercial Aspergillus IgG antibody assays have become pivotal in the current diagnosis of chronic pulmonary aspergillosis (CPA). However, diagnostic cutoffs have been found to vary from manufactures’ recommendations in different settings. This study aimed to establish the Aspergillus IgG reference range among Nigerians and determine a diagnostic cutoff for CPA. Methods: Sera from 519 prospectively recruited healthy blood donors and 39 previously confirmed cases of CPA were analysed for Aspergillus IgG levels using the Bordier test kit (Bordier Affinity Products SA, Crissier, Switzerland). Accuracy versus cutoff profile and receiver operating characteristics (ROC) curve were analysed for both CPA cases and controls using the R-Studio (2020), (Window desktop, version 4.0.2 software with R packages “nnet” and “ROCR”). Results: Among healthy blood donors, 141 (27.2%) were aged 16–25 years with median (interquartile range, IQR) of 22 (20–24) years; 304 (58.6%) were aged 26–40 years with median (IQR) of 32 (29–36) years; while 74 (14.2%) were aged 41–60 years with median (IQR) of 46 (44–49.75). Median IgG level in respective age groups were 0.069 (0.009–0.181), 0.044 (0.014–0.202) and 0.056 (0.01–0.265) with no significant difference found in the three age categories ( p = 0.69). The overall diagnostic cutoff for the diagnosis of CPA was 0.821 with an accuracy of 97.1% and area under the curve (AUC) = 0.986. Conclusion: The optimal diagnostic cutoff for diagnosing CPA in Nigerians using the Bordier kit was 0.821 which is lower than the manufacturer’s recommended cutoff of 1.0. The determination of this cutoff among Nigerians will significantly enhance accurate identification of CPA and assessment of its true burden in Nigeria.
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