The aim of this research study is to look at the body composition (such as muscle and fat) in people with chronic kidney disease (CKD) and comparing it with body composition is people without CKD. The investigators currently understand loss of muscle function and mass (sarcopenia) affect the general health of people as they age, but this process seems to be more common, accelerated, and occurs earlier in people with CKD. There is limited evidence in this area, and we believe that if we understand when and how sarcopenia affects people with CKD, investigators can guide future trials and treatments to help treat sarcopenia, and in turn improve quality of life and health outcomes in people with CKD.

In this study, the investigators will follow up people with CKD in two visits a year apart. In both visits, the investigators will measure the participants body composition and estimated kidney function using 2 different testing methods - Cystatin C eGFR and Creatinine eGFR. Using both the results in a formula, the creatinine muscle index can be calculated. If this index correlated with sarcopenia, it will be helpful tool in the care of people with CKD as will be a easy to use screening tool for sarcopenia in this population.

Inclusion Criteria:

Subjects capable of giving informed consent

≥18 years of age Chronic kidney disease stages 3-5 looked after in secondary care nephrology Healthy volunteers with normal kidney function (Control)

Exclusion Criteria:

• Pregnancy
• Subjects with known neuromuscular diseases, e.g. myopathy, muscular dystrophy, muscular atrophy
• Renal transplant recipients
• Patients with pacemakers

80 participants with different levels of renal function (normal renal function, CKD3,4 and 5) to be recruited from secondary care renal department.