Diagnostic Utility of Serum Krebs von den Lungen-6 (KL-6) and Surfactant Protein-D (SP-D) Levels in Hypersensitivity Pneumonitis

BACKGROUND: This study aimed to investigate the diagnostic and prognostic values of serum Krebs von den Lungen-6 (KL-6) and ve Surfactant Protein-D (SP-D) levels in patients with hypersensitivity pneumonitis (HP). METHODS: Serum samples were collected from patients diagnosed with HP and from a healthy control group. KL-6 and SP-D levels were measured using the ELISA method. HP cases were further compared according to fibrotic and non-fibrotic subgroups, as well as whether they were receiving treatment or not. The relationships between respiratory function tests (DLCO, FEV₁, FVC) and biomarker levels were examined. RESULTS: Both KL-6 (median 5.95 ng/ml vs 5.4 ng/ml, p<0.001) and SP-D (median 14.87 ng/ml vs 14.72 ng/ml, p<0.05) levels were significantly higher in HP patients than in the control group. In non-fibrotic HP patients, KL-6 levels were higher than in the fibrotic group (median 6.07 ng/ml vs 5.62 ng/ml, p<0.05), while no significant difference was observed for SP-D (p=0.71). KL-6 levels were significantly higher in untreated cases compared to treated cases (median 6.30 ng/ml vs 5.65 ng/ml, p<0.01), while the difference in SP-D was not significant (p=0.26). CONCLUSION: KL-6 emerges as a sensitive biomarker in the diagnosis of HP, assessing of disease activity, and monitoring treatment response. SP-D, although reflecting inflammatory processes, seems to be have limitations in evaluating fibrotic progression.