Background and Objectives The highly variable clinical course of interstitial lung disease (ILD) makes it difficult to predict patient prognosis. Serum surfactant protein-A (SP-A) and Krebs von den Lungen-6 (KL-6) are known prognostic biomarkers. However, the clinical or pathophysiological differences in patients with these biomarkers have not been well evaluated. We investigated the clinical and pathophysiological differences through the comparison of SP-A and KL-6 levels before and after treatment. Methods This study included retrospective data from 91 patients who were treated for ILD between August 2015 and September 2019. Serum SP-A and KL-6 levels were measured before and after treatment. The patients were followed up for 3 months. Results Changes in the serum biomarkers (Delta SP-A and Delta KL-6) were found to be significantly correlated (rs = 0.523, P < 0.001); Delta SP-A and Delta KL-6 were inversely correlated with changes in pulmonary function (% predicted values of diffusing capacity for carbon monoxide [DLCO], forced vital capacity [FVC], and forced expiratory volume in 1 s [FEV1]). Patients were divided into four groups based on their Delta SP-A and Delta KL-6 levels in a cluster analysis (G1, G2, G3, and G4). Both SP-A and KL-6 were elevated in the G1 group, with all the patients enrolled classified as progressive or unchanged, and 86.4% of patients showed improved disease activity in the G4 group, where both SP-A and KL-6 levels were reduced. In the G2 group, only SP-A levels decreased post-treatment, indicating an improvement in respiratory function; the patients were not at the end stage of the disease. Only the SP-A levels increased in the G3 group with immunosuppressive treatment. Conclusions Reduced serum SP-A and/or KL-6 levels are associated with improved lung function in patients with ILD. Some patients only showed a decrease in SP-A levels could prognosis an improvement in respiratory function. When only SP-A is increased, it may imply that the patients are at an early stage of disease progression. As a result, for proper disease monitoring, measuring both markers is important.

Background The sputum saccharide chain antigen (Krebs von den Lungen‐6 [KL‐6]) is a serum biomarker of lung injury. We aimed to evaluate the clinical performance of the automated immunoassay analyzer HISCL‐5000 in detecting KL‐6 by comparing it with LUMIPULSE G1200 and determine the diagnostic value of KL‐6 in interstitial lung disease (ILD). Methods A total of 145 serum samples from patients were tested using the two automated immunoassay analyzers in parallel. Results With a cutoff level of 500 U/mL, comparing the two systems, the agreement, sensitivity, specificity, and kappa value were 99.20%, 100%, 98.63%, and 0.984 (95% CI, 0.952‐1.000), respectively. Spearman's correlation and ICC showed that there was a strong correlation between serum KL‐6 levels measured by the two systems (rS = .991 [95% CI, 0.981‐0.995], ICC = 0.984 [95% CI, 0.978‐0.989], P < .01). The clinical diagnosis agreement rate in both systems was >80%. The kappa value was 0.707 (95% CI, 0.582‐0.832; SYSTEM B) and 0.707 (95% CI, 0.588‐0.826; SYSTEM A). The KL‐6 level in the ILD group (1339.5, 662.5‐2363) was significantly higher than that in the non‐ILD groups (252, 158.5‐353; Mann‐Whitney U = 381.5, P < .01), and the KL‐6 level (1558, 726‐2772.5) in the ILD group detected by SYSTEM A was significantly higher than that in the lung cancer group (339, 207‐424), other respiratory disease group (249, 194‐366), and control group (198, 131.5‐297; Kruskal‐Wallis H = 63.19, P < .01). Conclusions HISCL‐5000 showed well‐concordant results with those of HISCL‐5000 in the KL‐6 tests. In patients with ILD, KL‐6 showed a good diagnostic performance.

Background The highly variable clinical course of interstitial lung disease (ILD) makes it difficult to determine patients’ prognoses. Serum surfactant protein-A (SP-A) and Krebs von den Lungen-6 (KL-6) were known biomarkers as a monitor of the prognoses. However, the clinical or pathophysiological differences of those biomarkers are not well evaluated. Therefore, through the comparison of the changes of SP-A and KL-6 levels before and after treatment, we investigated the clinical or pathophysiological differences which are embodied by those markers. Methods This study included retrospective data for 71 patients treated for ILD at the First Affiliated Hospital of Guangzhou Medical University between August 2015 and September 2019. Serum SP-A and KL-6 levels were measured before and after treatment. The patients were followed for at least 3 months. Results Changes in the serum biomarkers (Delta SP-A and Delta KL-6) were significantly correlated (rS = 0.482, P < 0.001); Delta SP-A and Delta KL-6 were inversely correlated with changes in pulmonary function (P < 0.05). In a cluster analysis of delta SP-A and KL-6 levels, patients were classified into three groups. In the cluster analysis, in the group in which only SP-A levels decreased after treatment, 50.0% of patients recovered respiratory function and had a significant reduction of serum LDH levels.Conclusions Reduced serum SP-A and/or KL-6 levels were associated with improved lung function in patients with ILD. However, there were patients who showed only a reduction of SP-A levels after treatment. Thus, for proper disease monitoring, measuring both markers are important.