Relationship Between Total Body Protein and Cross-Sectional Skeletal Muscle Area in Liver Cirrhosis Is Influenced by Overhydration.

Sarcopenia as defined by reduced skeletal muscle area (SMA) on cross-sectional abdominal imaging has been proposed as an objective measure of malnutrition, and it is associated with both wait-list mortality and posttransplant complications in patients with cirrhosis. SMA, however, has never been validated against the gold standard measurement of total body protein (TBP) by in vivo neutron activation analysis (IVNAA). Furthermore, overhydration is common in cirrhosis, and its effect on muscle area measurement remains unknown. We aimed to examine the relationship between SMA and TBP in patients with cirrhosis and to assess the impact of overhydration on this relationship. Patients with cirrhosis who had undergone IVNAA and cross-sectional imaging within 30 days were retrospectively identified. Patients with significant clinical events between measurements were excluded. Psoas muscle area (PMA) and SMA at the level of the third lumbar vertebrae were determined. Total body water was estimated from a multicompartment model and expressed as a fraction of fat-free mass (FFM), as determined by dual-energy X-ray absorptiometry, to provide an index of hydration status. In total, 107 patients underwent 109 cross-sectional imaging studies (87 computed tomography; 22 magnetic resonance imaging) within 30 days of IVNAA. Median time between measurements was 1 day (IQR, -1 to 3 days). Between 43% and 69% of the cohort was identified as sarcopenic, depending on muscle area cutoff values used. TBP was strongly correlated with SMA (r = 0.78; P < 0.001) and weakly correlated with PMA (r = 0.49; P < 0.001). Multiple linear regression showed SMA was significantly and positively associated with FFM hydration (P < 0.001) independently of TBP. In conclusion, SMA is more closely related to TBP than is PMA, and it should be preferred as a measure of sarcopenia. Overhydration significantly affects the measurement of cross-sectional muscle area.