Serial measurements of KL-6 for monitoring activity and recurrence of interstitial pneumonia with anti-aminoacyl-tRNA synthetase antibody: A retrospective cohort study

The aim of this study was to evaluate whether serial measurements of serum Krebs von den Lungen-6 (KL-6) could be used to monitor disease activity and to detect recurrence in patients with interstitial pneumonia (IP) with anti-aminoacyl-tRNA synthetase antibodies (ARS-IP). This retrospective cohort study included 44 patients with ARS-IP. Thirty-six patients had serial data of blood tests and pulmonary function tests. Baseline and longitudinal analyses were performed to investigate whether lung function parameters were associated with serum biomarkers (KL-6, lactate dehydrogenase [LDH], and C-reactive protein [CRP]) using Pearson correlation coefficient. Additionally, the diagnostic accuracy of changes in these biomarkers for detecting ARS-IP recurrence was analyzed by receiver operating characteristic curve analysis. Baseline levels of serum KL-6 were significantly associated with vital capacity (VC) and diffusion capacity for carbon monoxide (DLco) (r = −0.40, P = .015, and r = −0.44, P = .010, respectively). Longitudinal changes in KL-6 were inversely correlated with changes in VC and DLco (r = −0.57, P <.001 and r = −0.42, P <.001, respectively), whereas those in LDH and CRP were not. Moreover, longitudinal changes in serum KL-6 were significantly associated with recurrence of ARS-IP and could be used to detect ARS-IP recurrence; the area under the curve was 0.79 (P = .002). The present study demonstrated that serial measurement of KL-6 is useful for monitoring disease activity and detecting recurrence of ARS-IP.