Techniques for the diagnosis of sarcopenia.

Sarcopenia is an age-related process of skeletal muscle loss associated with declining physical performance, highly prevalent among older subjects, with a negative prognostic effect on falls, disability and mortality risk. Modern approaches to sarcopenia case finding and diagnosis are based on physical performance measures, while assessment of muscle mass represents the second diagnostic step. Muscle mass can be quantified at different levels of body composition, with a complexity increasing from atomic detection to anatomic measure. In the choice of measuring method, different factors have to be taken into account, including validity, simplicity, cost and specific purpose (clinical versus research). Some methods, such as MRI and CT, have high validity but are complex and costly. Bioelectrical impedance analysis is inexpensive and easy to perform in most settings, being the preferred method for clinical practice. Dual energy X-ray absorptiometry has intermediate cost and complexity with good reproducibility, and is more reliable for research setting. Other methods, such as administration of tritium (D3)-marked creatine and measurement of urinary D3-creatinine, are still in a preclinical phase of development. For all methods the issue of normative data does exist and needs to be solved, in order to reliably identify homogeneous populations with sarcopenia, to be targeted in clinical practice and intervention studies.