Creatinine Muscle Index as a Novel Muscle Mass Indicator in Patients With Chronic Kidney Disease

Background

The early detection of muscle loss in patients with chronic kidney disease (CKD) is crucial. The creatinine muscle index (CMI, mg/day/1.73 m²), which is calculated as the product of serum creatinine, is easily available in daily care and estimates the muscle mass. However, the association between CMI and muscle mass has not been fully assessed. We aimed to investigate whether CMI can serve as a predictor of muscle mass in patients with CKD.

Methods

This cross-sectional study included patients with CKD undergoing kidney biopsy and plain computed tomography (CT) to assess the kidney morphology. Muscle mass was assessed using the psoas muscle index, determined by dividing the cross-sectional psoas muscle area at the L3 level, measured by manual tracing on pre-biopsy CT, by the participant's height (cm²/m²).

Results

In total, 159 participants (84 male [52.8%], mean age 51.7 ± 16 years) were included. CMI was positively correlated with PMI in men (r = 0.37, p < 0.01) and women (r = 0.56, p < 0.01). The prevalence of low muscle mass was 55 (65.5%) in men and 44 (58.7%) in women. The odds ratios (ORs) and 95% confidence intervals (CIs) for low muscle mass were significantly higher in Tertile 1 of CMI than in Tertile 3 in both men and women (OR, 5.37 [95% CI, 1.32–21.8] in men; OR, 7.31 [95% CI, 1.38–38.6] in women) after adjusting for age, body mass index and co-morbidities (hypertension and diabetes). According to receiver operating characteristics curves, the optimal cut-off value of CMI for low muscle mass was 1079 mg/day/1.73 m² (area under the curve 0.69 [95% CI: 0.57–0.81]; sensitivity, 0.78; specificity, 0.62) in men and 693 mg/day/1.73 m² (area under the curve 0.74 [95%CI: 0.63–0.85]; sensitivity, 0.57; specificity, 0.90) in women.

Conclusions

CMI is significantly associated with muscle mass in patients with CKD. Our findings suggest the utility of CMI for screening the muscle mass in this population.