Sarcopenia and liver transplant: The relevance of too little muscle mass

Table 1 Methods used to define muscle mass or function in cirrhosis

Method	Measurements obtained	Limitations	Notations
Multiple (four) compartment model	Total body water	Requires combinations of methods (such as water dilution, densitometry)	Best model for cirrhosis when fluid overload is present
	Body fat
	Fat free dry matter (protein)
	Bone mineral content
Dual X-ray Absorptiometry	Body fat Fat free body mass Bone mineral content	Limited ability to differentiate between lean tissue and body water with excess body water resulting in overestimation of fat free mass[1]	Peripheral measures of lean tissue are less impacted by ascites[24,26]
		Ascites, especially more than 4 liters, can significantly impact truncal measures[26,27]
Cross sectional imaging	Estimate skeletal muscle volume	Can be used to determine differences in skeletal muscle between groups[31] Studies use different muscle groups, anatomic levels and cutoff values to diagnose sarcopenia	Measurements 5 cm above the level of the 4th-5th lumbar vertebra had the highest correlation with total body skeletal volume[31]
Biochemical methods	Skeletal muscle mass	Total body protein is a measure of functional muscle mass and can be done through techniques such as in vivo neutron activation analysis 24 h urine creatinine is one method, but is limited in cirrhosis where renal insufficiency is common[93]	Use calculations based on these methods to quantify muscle mass
Bioelectrical impedence analysis	Fat free mass Fat mass	Guidelines recommend against routine use of BIA under states of altered hydration[94]	Segmental BIA was found to have a better correlation and lower standard error in estimating body cell mass in the setting of cirrhosis without ascites but still performs poorly with ascites present[95]
		BIA estimates of total body water were found to be accurate in cirrhotic patients without ascites, but performed poorly when ascites was present[23]	Phase angle can be used. In a study including participants with a wide range in severity of liver disease, phase angle was positively correlated with total body protein, muscle mass and muscle strength[96]
Anthropometry	Estimate muscle mass	Edema alters results of anthropometry overestimating muscle mass[8]	Mid arm circumference was found to be one of the most accurate anthropometric measures[29] and was most predictive of clinical outcomes[97]
Functional Measures	Measures ability to perform physical task, for which muscle function is one component	Common functional measures assess all systems involved in exercise including cardiovascular, pulmonary, hematologic, neurologic and musculoskeletal[33]	Include tests such as submaximal cardiopulmonary fitness tests, six minute walk test, hand grip strength and isokinetic strength of flexion and extension at different joints Often simple tests such as hand grip correlate with measures of skeletal muscle[29]

BIA: Bioelectrical impedance analysis.