Measuring sarcopenia in people living with HIV

The 14th International Workshop on HIV and Ageing included an oral presentation by Dr Peggy Cawthon that discussed methods for measuring sarcopenia. [1]

Sarcopenia is loss of muscle mass and a hallmark of ageing that occurs even with regular exercise. Also, although sarcopenia is associated with important reductions in muscle size, strength and function, there is no consensus definition based on target levels of these factors.

Methods to measure muscle mass include DEXA (dual x-ray absorptiometry) scans, bioimpedance analysis (BIA), CT scans and D3-creatinine dilution. Muscle function or strength is assessed using grip strength, walking speed and self-reported disability or limitations. As a marker, grip strength is usually preferred due to low cost and quick test time, whereas lower extremity tests tend to be more subjective and have limitations in older people.

DEXA scans measure bone mineral density (BMD) and fat mass and can be used to indirectly approximate muscle mass. Dividing DEXA values of appendicular (legs and arms only) by height can be used as way to predict the risk of sarcopenia. Sarcopenia is defined as any result below 7.26 kg/m² for men or 5.45 kg/m² for women.

Reviews using meta-analyses have not shown a strong predictive link between DEXA-derived muscle mass and functional outcomes. Furthermore, interventional studies show maintenance of strength despite weight loss in participants with osteoarthritis or diabetes. DEXA is a highly subjective measure and prone to measurement errors.

Direct measurements of muscle mass can be calculated by measuring urine creatinine as 98% of creatine is stored in muscle tissue and levels are stable. Creatine levels are therefore proportional to muscle mass.

The D3-creatine dilution test is used to ascertain total muscle mass. Briefly, a 30 mg oral dose of labelled creatine is given, which is processed to creatinine and reaches steady state within three to six days. Urine D3-creatinine:creatinine ratio is used to calculate muscle mass. Higher D3-creatinine ratios correspond to lower muscle mass.

In the MrOS implementation study of 1400 men, measurement of muscle mass by DEXA or D3-creatinine correlated (r=0.66), but DEXA overestimated muscle mass. People with lower grip strength and walking speed had lower muscle mass calculated by the D3-creatine method. Similar outcomes were observed for women in the SOMMA study of 875 people aged >75 years.

There is similarly no standardised measure of sarcopenia in people living with HIV, including those who are older. Current approaches recommend collecting multiple components to cover muscle function, size, physical performance, self-reported disability and fitness.