Creatinine/cystatin C ratio as a surrogate marker of residual muscle mass in amyotrophic lateral sclerosis

Aim Identification of sensitive surrogate markers that indicate disease progression in amyotrophic lateral sclerosis might be useful in clinical trials and clinical care. Determination of the creatinine/cystatin C (Cr/CysC) ratio eliminates the effect of renal function on serum creatinine levels; therefore, we considered that the ratio might serve as a surrogate marker of residual muscle mass. We studied the Cr/CysC ratio as a useful surrogate marker of residual muscle mass in patients with amyotrophic lateral sclerosis. Methods A total of 103 participants were recruited: 62 patients with amyotrophic lateral sclerosis and 41 healthy controls. Serum levels of Cr and CysC were measured in both groups. We subsequently investigated the correlation between the Cr/CysC ratio and disease severity in patients with amyotrophic lateral sclerosis. Results The ratio was significantly lower in the amyotrophic lateral sclerosis group than in the control group. Furthermore, the ratio decreased as the severity of amyotrophic lateral sclerosis increased. The Cr/CysC ratio might be a better and more reliable method than the serum Cr level as a means of monitoring residual muscle mass of the entire body in patients with amyotrophic lateral sclerosis. Conclusion The present results show that the Cr/CysC ratio might be a suitable candidate for a useful and quantitative surrogate marker for the assessment of disease severity and progression in patients with amyotrophic lateral sclerosis.