Serum KL-6 as a biomarker to predict progression at one year in interstitial lung disease.

About one third of non-IPF ILD patients progresses over time. Serum KL-6, a lung epithelial mucin type 1, is an established marker to assess disease severity in ILD but its ability to predict progression needs to be further explored. To investigate whether serum KL-6 is of additional value to stratify the patients for the risk of developing clinical or functional progression at one year. ILD patients from 6 European centers were retrospectively enrolled. Disease progression was defined as relative decline ⩾10% in FVC or ⩾15% in DLco from baseline. Serum KL-6 was measured using a full-automated chemiluminescent immunoassay (Fujirebio). Comparative logistic regression was used to identify predictors of progression at one year. 303 patients were included. 37% developed progression after one year from KL-6 measurement. A stepwise selection was used to identify and include five predictors of progression in a risk score: age, gender, BMI, FVC, and KL-6. The final model was superior to KL-6 alone to predict progression at one year, with 55% sensitivity, 73% specificity and 67% accuracy at a cut-off of 5. Patients were stratified in low and high risk of progression at one year based on the cut-off of 5, with a similar accuracy for IIP 0.687 and CTD-ILD 0.720 but not for HP. Serum KL-6 levels, included in a risk score with other clinical and functional variables, may help to better stratify patients for the risk of disease progression at one year, compared to any individual predictor.