Low muscle strength is common among kidney transplant recipients (KTRs) and it is independently associated with a poor outcomes, according to investigators.

In a prospective longitudinal study that enrolled 128 KTRs at least 1 year after transplantation, Winnie Chan, PhD, University Hospitals Birmingham in the United Kingdom, and collaborators found that 82 patients (64%) had low muscle strength, and this was significantly associated with a nearly 2.5-fold increased risk of a composite end point of mortality and hospitalization compared with normal muscle strength after adjusting for multiple potential confounders. Low muscle strength also was significantly associated with diminished physical- and mental-related quality of life (QoL). The study found no significant association between the composite outcome and low muscle mass, sarcopenia, and obesity. Low muscle mass and sarcopenia, but not obesity, were significantly associated only with inferior physical health-related QoL.

“This study presents the first compelling independent association between decreased muscle strength and adverse clinical outcomes in kidney transplantation,” Dr Chan’s team wrote in a paper published in the Journal of Renal Nutrition. “Muscle strength assessment in routine clinical practice may serve as a novel tool for improving risk stratification in prevalent KTRs, setting the scene for future interventional research and therapeutic targets.”

The investigators said their findings imply causal relationships between muscle strength and clinical outcomes and health-related QoL, “justifying interventional strategies to improve muscle strength in KTRs.”

Dr Chan and her colleagues identified increased muscle mass, higher levels of hemoglobin and vitamin D, higher protein intake, and increased physical activity as modifiable independent predictors of increased muscle strength.

The mean age of the 138 patients was 49 years, but it was significantly higher among those with low compared with normal muscle strength (52 vs 45 years). The study population was 56% men and 78% Caucasian. The patients had a median time post-transplantation of 5 years. The median follow-up duration was 64 months.

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The investigators defined low muscle strength using gender-specific handgrip strength cutoffs derived from a reference population—less than 30 kg for men and less than 20 kg for women—a definition applied in the chronic kidney disease literature. The investigators evaluated health-related QoL using the Medical Outcomes Study Short Form-36 questionnaire.

The authors acknowledged that the study’s small number of patients selected from a single center is a limitation. They also pointed out that “the inherent observational nature of the study precludes the establishment of causality between muscle strength and clinical outcomes.”

Reference

Chan W, Chin SH, Whittaker AC, et al. The associations of muscle strength, muscle mass, and adiposity with clinical outcomes and quality of life in prevalent kidney transplant recipients. J Ren Nutr. 2019.  doi: 10.1053/j.jrn.2019.06.009