BackgroundSerum cryptococcal antigen (CrAg) test is the most used noninvasive method to detect cryptococcal infection. However, false-negative CrAg test is not uncommon in clinical practice. Then, the aim of this study was to investigate the factors associated with false-negative CrAg test among non-human immunodeficiency virus (HIV) adult patients with pulmonary cryptococcosis and its clinical features.

MethodsOne hundred and fourteen non-HIV adult patients with pulmonary cryptococcosis, proven by biopsy, were retrospectively reviewed. Finally, 85 patients were enrolled; 56 were CrAg positive (CrAg+ group) and 29 were negative (CrAg- group). It was a cross-sectional study. Then, baseline characteristics, underlying diseases, clinical symptoms, laboratory findings, and chest radiological findings were reviewed and analyzed. Chi-square test was used to analyze categorical variable. Odds ratio (OR) was used to measure correlation. Student's t- test was obtained to analyze continuous variable.

ResultsNo difference in baseline characteristics, underlying diseases, clinical symptoms, and laboratory findings were found between two groups (P > 0.05 in all). Nevertheless, diffuse extent lesion was 82.1% in CrAg+ group and 10.3% in CrAg- group (χ = 40.34, P < 0.001; OR = 39.87).

ConclusionsAmong patients with limited pulmonary involvement, a negative serum CrAg does not preclude the diagnosis of pulmonary cryptococcosis. However, among patients with extensive pulmonary involvement, serum CrAg is a useful diagnostic tool for pulmonary cryptococcosis. Furthermore, we also noticed that the untypical and mild presentations with extensive pulmonary lesion might be the features of pulmonary cryptococcosis, which needs further investigation.