KL‐6: a serological biomarker for interstitial lung disease in patients with polymyositis and dermatomyositis

<jats:p><jats:bold>Abstract. </jats:bold> Fathi M, Barbasso Helmers S, Lundberg IE (Karolinska University Hospital, Stockholm; Karolinska Institutet, Karolinska University Hospital, Stockholm; and Institute of Environmental Medicine, Karolinska Institutet, Stockholm; Sweden). KL‐6: a serological biomarker for interstitial lung disease in patients with polymyositis and dermatomyositis. <jats:italic>J Intern Med</jats:italic> 2012; <jats:bold>271</jats:bold>: 589–597.</jats:p><jats:p><jats:bold>Objectives. </jats:bold> To investigate whether Caucasian patients with polymyositis (PM) or dermatomyositis (DM) and interstitial lung disease (ILD) have elevated serum levels of KL‐6 compared with patients without ILD and whether KL‐6 could be used as a marker for ILD activity and treatment efficacy of ILD in PM/DM.</jats:p><jats:p><jats:bold>Design and methods. </jats:bold> Thirty patients with PM/DM (seven with ILD) and 17 age‐ and sex‐matched healthy controls were included in a retrospective, cross‐sectional analysis. Twelve patients were followed for longitudinal evaluation. ILD was defined as restrictive lung function impairment with radiographic signs of ILD. Serum KL‐6 levels were measured using a sandwich enzyme immunoassay kit. Groups were compared by Mann–Whitney <jats:italic>U</jats:italic>‐test.</jats:p><jats:p><jats:bold>Results. </jats:bold> PM/DM patients with ILD had significantly higher median serum KL‐6 levels compared with those without ILD: 995 (range 533–2318) versus 322 (range 132–1225) U mL<jats:sup>−1</jats:sup> (<jats:italic>P </jats:italic>= 0.0002). Median serum levels of healthy controls were 225 (range 136–519) U mL<jats:sup>−1</jats:sup>. Serum levels of KL‐6 were inversely correlated with percentages of forced expiratory volume in 1 s (FEV<jats:sub>1</jats:sub>), vital capacity (VC), total lung capacity (TLC), forced VC, diffusing capacity of carbon monoxide (DLco), maximal voluntary ventilation at 40 breaths min<jats:sup>−1</jats:sup> and residual volume (RV). Changes in KL‐6 levels showed a significant inverse correlation with changes in percentage FEV<jats:sub>1</jats:sub>, TLC, DLco and RV. At a cut‐off level of 549 U mL<jats:sup>−1</jats:sup> (mean ± 2.5 SD for controls), the sensitivity and specificity for diagnosis of ILD were 83% and 100%, respectively.</jats:p><jats:p><jats:bold>Conclusion. </jats:bold> The level of serum KL‐6 may serve as measure of ILD in patients with PM/DM and is a promising biomarker for use in clinical practice to assess clinical response to treatment.</jats:p>