Study of Clara cell 16, KL-6, and surfactant protein-D in serum as disease markers in pulmonary sarcoidosis

Study objectives: To determine the discriminative value of serum Clara cell 16 (CC 16), KL-6, and surfactant protein (SP)-D as markers of interstitial lung diseases, and their ability to reflect pulmonary disease severity and prognosis in sarcoidosis. Subjects: Seventy-nine patients with sarcoidosis and 38 control subjects. Measurements: Serum CC16, KL-6, and SP-D concentrations at disease presentation were measured. Pulmonary function tests and chest radiographs were analyzed at presentation and 2-year follow-up. Results: All markers co-correlated, and a significant difference was found between CC16, KL-6 (Krebs von den Lungen-6), and SP-D levels in patients with sarcoidosis and control subjects (p < 0.0001). Receiver operating characteristic curve analysis revealed largest area under the curve for KL-6. Significantly higher levels of CC16 and KL-6 were found in patients with parenchymal infiltration (stage II, III) compared to patients without parenchymal infiltration (stage 1). In concordance, CC16 and KL-6 levels inversely correlated with diffusion capacity and total lung capacity, and KL-6 also with inspiratory vital capacity. Moreover, higher KL-6 levels were weakly but significantly associated with persistence or progression of parenchymal infiltrates at 2-year follow-up. Conclusion: In this study, KL-6 appears to be the best discriminative marker in differentiating patients with sarcoidosis from healthy control subjects; however, as it is not a specific marker for this condition, this quality is unlikely to be useful as a diagnostic tool. Both CC16 and KL-6 may be of value in reflecting disease severity, and KL-6 tends to associate with pulmonary disease outcome.