# Skeletal muscle-kidney crosstalk in a cohort of critical illness survivors

## TL;DR

This study explores the link between muscle health and kidney function in people who survived severe COVID-19.

## Contribution

The study reveals a connection between skeletal muscle mass and kidney function in long-term COVID-19 survivors.

## Key findings

- Higher calf circumference and thigh muscle thickness were linked to better kidney function (eGFR).
- Sarcopenia was not independently associated with poor kidney function markers like low eGFR or albuminuria.

## Abstract

The skeletal muscles and kidneys are frequently affected during critical illness; however, their crosstalk remains poorly explored, especially in the long-term evolution. Therefore, we investigated the crosstalk between skeletal muscle and kidney function in COVID-19 survivors.

A cross-sectional analysis of a prospective cohort study with survivors of moderate to severe COVID-19 hospitalization. Skeletal muscle assessments included handgrip strength, calf circumference, ultrasound-measured quadriceps thickness, and gait speed test. Sarcopenia was diagnosed by modified EWGSOP2 (low handgrip strength plus low ultrasound-measured quadriceps thickness). Kidney function was assessed by estimated glomerular filtration rate (eGFR), urinary albumin-to-creatinine ratio (UACR), and urine sediment analysis. Abnormal kidney function was defined as an eGFR < 60 mL/min/1.73m2, albuminuria (≥30 mg/g), and/or leukocyturia or hematuria.

A total of 734 survivors (46% female, 43% ≥ 60 years, 35% with diabetes) were assessed 7 ± 2 months post-hospital discharge. Sarcopenia was diagnosed in 21.4% of the cohort. Positive significant associations with eGFR were observed for calf circumference (β = 0.42 ml/min/1.73m2, 95%CI: 0.06 to 0.78) and thicknesses (mm) of rectus femoris (β = 0.47, 95%CI: 0.01 to 0.94) and vastus intermedius (β = 0.55, 95%CI: 0.14 to 0.96). None of the skeletal muscle parameters were associated with UACR (mg/g). Survivors with sarcopenia had lower eGFR (‒5.8 ml/min/1.73m2, 95%CI: ‒10.8 to ‒0.9), but similar frequencies of low eGFR (24% vs. 18%; p = 0.137), albuminuria (27% vs. 31%; p = 0.434) and abnormal urine sediment (17% vs. 22%; p = 0.217) as compared to those without sarcopenia. Sarcopenia was not associated with higher odds of low eGFR, albuminuria, or abnormal urine sediment.

In survivors of moderate to severe COVID-19 hospitalization, skeletal muscle mass was associated with eGFR, whereas sarcopenia per se was not independently associated with poor kidney function. These findings suggest the existence of a skeletal muscle-kidney crosstalk in this population.