Background  At present, there is no clear consensus on the diagnostic criteria of sarcopenia. Using bioelectrical impedance analysis (BIA) to obtain the phase Angle (PhA) can reflect the body function to a certain extent and predict the risk of sarcopenia.

  Objective  To explore the diagnostic value and significance of PhA measured by BIA in different diagnostic criteria for sarcopenia.

  Methods  A total of 1 009 eligible older men over 60 years old from several communities of Beijing were included. PhA at 50 kHz was measured by BIA and other parameters related to muscle function were recorded. Organizations such as the Asian sarcopenia working group, the European sarcopenia working group, the international sarcopenia working group, and the National Institutes of Health Foundation had developed and updated the diagnostic criteria for sarcopenia, so these criteria were used to diagnose sarcopenia. The correlations between PhA and the diagnostic components of sarcopenia were analyzed through spearman correlation analysis and multiple regression analysis. Univariate and multivariate logistics regression were used to illustrate the correlation between PhA and sarcopenia. Finally, the diagnostic value of the PhA was determined according to the AUC area, and the Youden index was calculated to determine the best cut-off value of the PhA.

  Results  The mean PhA in 1009 older men was 4.38° ± 0.16°. The prevalence of sarcopenia ranged from 2.3% to 12.2% using the 6 criteria. With the increase of age, the value of PhA decreased, while the prevalence of sarcopenia gradually increased. In the correlation analysis, the PhA was significantly correlated with the components of diagnostic criteria to sarcopenia. Multiple linear regression showed that the PhA was linearly correlated with age, skeletal muscle mass index (SMI), grip strength, gait speed and short physical performance battery (SPPB)(P＜0.05, R²=0.563). Multivariate logistic regression analysis showed that among all diagnostic criteria, age (OR＞1, P＜0.05) and PhA (OR＜1, P＜0.05) were significantly associated with sarcopenia. The cut-off values of the PhA in predicting sarcopenia ranged from 4.15° to 4.55°.

  Conclusion  PhA is moderately correlated with age, grip strength, SMI and body function. Moreover, in all diagnostic criteria, advanced age and low PhA are associated with sarcopenia. In general, the PhA is easy to measure, and can be used for early prediction and diagnosis of sarcopenia in the elderly who can not receive functional tests .