Diagnostic performance of specific biomarkers for interstitial lung disease: a single center study.

Objectives: This study aimed to determine the clinical significance of Krebs von den Lungen-6 (KL-6), surfactant proteins A (SP-A) and D (SP-D) in the evaluation and management of interstitial lung disease (ILD).

Methods: Serum KL-6, SP-A, SP-D levels were measured in 122 unique consecutive patients referred for connective tissue disease (CTD) associated ILD (CTD-ILD) autoantibodies and 120 "healthy" controls. Patients' charts were retrospectively reviewed and categorized as ILD and non-ILD or CTD-ILD and other ILD. All biomarkers were evaluated for diagnosis and moderate vs. severe ILD based on high-resolution computed tomography (HRCT).

Results: ILD was diagnosed in 52 % (n=64) and non-ILD in 48 % (n=58). ILD patients were categorized as other ILD (61 %, n=39) or CTD-ILD (39 %, n=25). Patients with ILD had significantly elevated levels of SP-A (p<0.02), KL-6 or SP-D (both p<0.0001) when compared to those with non-ILD. The mean levels of all biomarkers were significantly elevated levels in the ILD compared to non-ILD group (p<0.0001). No significant difference in biomarker levels between CTD-ILD and other ILD groups (p≥0.900). Biomarkers had comparable specificities (89-93 %) however; sensitivities were variable at 75 , 77 and 17 % for KL-6, SP-D and SP-A, respectively. Combination of KL-6 and SP-D yielded comparable diagnostic accuracy to all biomarkers with median levels significantly higher in patients with severe vs. mild disease.

Conclusions: KL-6 and SP-D levels are elevated in ILD and therefore contribute to the diagnosis and risk stratification for patient management.