Associations of Creatinine Muscle Index with markers of sarcopenia and mortality in chronic kidney disease: A prospective cohort study

BACKGROUND: Sarcopenia is common in chronic kidney disease (CKD) and linked to higher mortality, but identifying those at risk remains challenging. Indices combining serum creatinine and cystatin C (eGFRratio and eGFRdifference) have been studied, but have tended to perform worse in those with CKD. This study aimed to examine the relationship of Creatinine Muscle Index (CMI), an estimate of glomerular filtration of creatinine, with sarcopenia and mortality in a non-dialysis CKD population. METHODS AND FINDINGS: NURTuRE-CKD is a prospective, multicentre cohort study of people with non-dialysis CKD in the UK. Two thousand nine hundred ninety-six individuals were enrolled between July 2017 and September 2019. Cystatin C measurements were available in 2,930 adults. CMI (mg/day) was calculated as eGFR cystatin C × serum creatinine concentration. The relationships between CMI and: (1) probable sarcopenia (defined as the best hand grip strength of