The Copenhagen PROTECT Study: Biomarkers for Length of Hospital Stay and Loss of Muscle Mass and Function in Old Medical Patients

As humans age, there is a gradual loss of skeletal muscle mass and strength, termed sarcopenia. The underlying causes of sarcopenia are yet not fully elucidated but are thought to be multifactorial and include increased levels of systemic pro-inflammatory mediators, a decrease in anabolic hormones and changes in the neuromuscular system. Furthermore, physical inactivity, chronic diseases, immobilisation and hospitalisation are known to play an important part in the development of sarcopenia.

The prevalence of sarcopenia ranges from 20-30% (aged >70yrs) within the general community. However, the prevalence of sarcopenia in geriatric patients after an acute hospital admission is substantially higher, estimated at ≈50%. Furthermore, successive events of hospitalisation have been suggested to contribute to the development of sarcopenia, as even short periods (4-5 days) of skeletal muscle disuse are known to induce muscle atrophy.

Mean length of hospital stay in geriatric wards due to acute illness or hip-fracture is typically 7 to 11 days during which the level of physical activity is strongly reduced leading to an accelerated loss of muscle mass that many older patients never recover from.

Notably, a substantial part of the deterioration in functional capacity could be avoided just by counteracting loss of muscle mass during hospitalization. As such, we need to identify sensitive biological, clinical and functional biomarkers predicting loss of muscle mass and function during hospitalization to identify patients at risk of developing sarcopenia. Additionally, it is crucial to investigate the association of these biomarkers with hospital length of stay, as hospitalisation has been suggested to contribute to the development of sarcopenia while longer hospital stays may increase patient risk of hospital-acquired infections and place an economic burden on society.