Muscle mass is a critical indicator for malnutrition and sarcopenia assessment. Anthropometric measurements like calf circumference (CC) could be a simple and cost-effective alternative when gold standard methods are not available. However, CC is probably less accurate for estimating muscle mass in female patients and patients with obesity. This study investigates whether adjusting CC using mid-upper arm circumference (MUAC) improves muscle mass estimation in patients with obesity. If validated, this correction method would serve as a simple clinical tool for muscle mass assessment.

The patient's demographic data including age, sex, primary diagnosis, and diagnoses of co-morbidities are found by the investigator in the medical history (eHL). The researcher codes the current main diagnosis and its severity: we use the World Health Organization's ICD-11 classification (icd.who.int/browse11/l-m/en) and a three-point scale where 1 is mild and 3 is severe.

The patient will be interviewed for changes in body weight and food intake. Anthropometric measurements will be recorded, including height, weight, body mass index (BMI), mid upper arm circumference, calf circumference, and waist circumference.

The accurate muscle mass measurement will be done using total body densitometry (DEXA) scan, that was already ordered for other purposes. Bone mineral density (BMD) from DEXA scan will be recorded. This allows us to see if calf circumference can be used for estimating bone mineral density. Patients will be followed up one year after data collection. Follow up will involve calling the patients and asking them questions from the SarQoL (sarcopenia quality of life questionnaire)

Calf circumference will be measured using non-elastic tape at the widest part of the dominant calf in the seated position with the weight evenly distributed on both feet (1). Mid upper arm circumference will be measured at the midpoint between the acromial surface of the scapula and the olecranon process of the elbow over the dominant arm when bent at 90 degrees. Waist circumference will be measured using measuring tape 2.5 cm above the umbilicus in a standing position. Waist circumference is used to define obesity as it is a marker of abdominal obesity (2). We aim to keep the interview no longer than 10 minutes.

Demographic and anthropometric data will be analyzed using descriptive statistics. The sensitivity, specificity of muscle mass measurements will be calculated. Corrected calf circumference will be compared to DEXA (gold standard diagnostic tool) and new cutoffs will be defined by using Receiver Operating Characteristic curves. Statistical analyses will be performed using R.

Inclusion Criteria:

Booked to undergo bone density scanning (DEXA) at Tartu University Hospital

Exclusion Criteria:

Isolation for infectious disease Pregnancy and lactation Unable to understand or follow study protocol

Patients of the internal medicine clinic for whom diagnostic bone density scanning (DEXA) has been requested by the physician normally responsible for the patient's care

Confidentiality issues prevent full access but we anticipate making anonymised data available to other investigators