Background: The serum creatinine / cystatin C (Cr/CysC) ratio has attracted attention as a marker for sarcopenia, but has not been studied in patients with idiopathic pulmonary fibrosis (IPF). This study aimed to confirm the utility of the serum Cr/CysC ratio in predicting sarcopenia and to investigate its clinical relevance.
Methods: This cross-sectional study prospectively enrolled patients with stable IPF. IPF was diagnosed through multidisciplinary discussions according to the 2018 international guidelines, and sarcopenia was diagnosed according to the 2019 consensus report of the Asian Working Group for Sarcopenia. Patient-reported outcomes (PROs) were evaluated using the modified Medical Research Council (mMRC) dyspnea scale, chronic obstructive pulmonary disease assessment test (CAT), and King’s Brief Interstitial Lung Disease (K-BILD) questionnaire. The associations between serum Cr/CysC ratio and the presence of sarcopenia and other clinical parameters, including PROs scores, were examined.
Results: A total of 49 Japanese patients with IPF with a mean age of 73.0 ± 7.7 years and a percent predicted forced vital capacity of 80.4 ± 15.5%, were enrolled. Sarcopenia was diagnosed in 18 patients (36.7%), and the serum Cre/CysC ratio was 0.86 [0.76–0.94] (median [interquartile range]). Receiver operating characteristic curve analyses for detection of sarcopenia according to the serum Cr/CysC showed that the area under the curve, optimal cutoff value, specificity, and sensitivity were 0.85, 0.88, 0.65, and 0.94, respectively. Sarcopenia was identified in 13% of patients with a high serum Cr/CysC ratio (≥0.88) and 60% with a low serum Cr/CysC ratio (<0.88) (P<0.001). Multiple linear regression analysis showed that the serum Cr/CysC ratio was an independent predictive marker of worse PROs evaluated using mMRC (P<0.05), CAT (P<0.05), and K-BILD (P<0.05).
Conclusions: This study showed that the serum Cr/CysC ratio can be used as a surrogate marker of sarcopenia in patients with IPF. Furthermore, it is important to pay attention to the serum Cr/CysC ratio because a lower serum Cr/CysC ratio is associated with worse PROs.