Accuracy of surrogate methods to estimate skeletal muscle mass in non-dialysis dependent patients with chronic kidney disease and in kidney transplant recipients.

BACKGROUND & AIMS: Bioelectrical impedance analysis (BIA) and anthropometric predictive equations have been proposed to estimate whole-body (SMM) and appendicular skeletal muscle mass (ASM) as surrogate for dual energy X-ray absorptiometry (DXA) in distinct population groups. However, their accuracy in estimating body composition in non-dialysis dependent patients with chronic kidney disease (NDD-CKD) and kidney transplant recipients (KTR) is unknown. The aim of this study was to investigate the accuracy and reproducibility of BIA and anthropometric predictive equations in estimating SMM and ASM compared to DXA, in NDD-CKD patients and KTR. METHODS: A cross-sectional study including adult NDD-CKD patients and KTR, with body mass index (BMI) ≥18.5 kg/m2. ASM and estimated SMM were evaluated by DXA, BIA (Janssen, Kyle and MacDonald equations) and anthropometry (Lee and Baumgartner equations). Low muscle mass (LowMM) was defined according to cutoffs proposed by guidelines for ASM, ASM/height2 and ASM/BMI. The best performing equation as surrogate for DXA, considering both groups of studied patients, was defined based in the highest Lin's concordance correlation coefficient (CCC) value, the lowest Bland-Altman bias (<1.5 kg) combined with the narrowest upper and lower limits of agreement (LoA), and the highest Cohen's kappa values for the low muscle mass diagnosis. RESULTS: Studied groups comprised NDD-CKD patients (n = 321: males = 55.1%; 65.4 ± 13.1 years; eGFR = 28.8 ± 12.7 ml/min) and KTR (n = 200: males = 57.7%; 47.5 ± 11.3 years; eGFR = 54.7 ± 20.7 ml/min). In both groups, the predictive equations presenting the best accuracy compared to DXA were SMM-BIA-Janssen (NDD-CKD patients: CCC = 0.88, 95%CI = 0.83-0.92; bias = 0.0 kg; KTR: CCC = 0.89, 95%CI = 0.86-0.92, bias = -1.2 kg) and ASM-BIA-Kyle (NDD-CKD patients: CCC = 0.87, 95%CI = 0.82-0.90, bias = 0.7 kg; KTR: CCC = 0.89, 95%CI = 0.86-0.92, bias = -0.8 kg). In NDD-CKD patients and KTR, LowMM frequency was similar according to ASM-BIA-Kyle versus ASM-DXA. The reproducibility and inter-agreement to diagnose LowMM using ASM/height2 and ASM/BMI estimated by BIA-Kyle equation versus DXA was moderate (kappa: 0.41-0.60), in both groups. Whereas female patients showed higher inter-agreement (AUC>80%) when ASM/BMI index was used, male patients presented higher AUC (70-74%; slightly <80%) for ASM/height2 index. CONCLUSIONS: The predictive equations with best performance to assess muscle mass in both NDD-CKD patients and KTR was SMM-BIA by Janssen and ASM-BIA by Kyle. The reproducibility to diagnose low muscle mass, comparing BIA with DXA, was high using ASM/BMI in females and ASM/height2 in males in both groups.

Sarcopenia and its components in adult renal transplant recipients: prevalence and association with body adiposity.

Sarcopenia is a progressive and generalised skeletal muscle disorder associated with adverse outcomes. Ageing causes primary sarcopenia, while secondary causes include chronic kidney disease (CKD), long-term use of glucocorticoids and obesity. The aim of the present study was to evaluate the prevalence of sarcopenia using guidelines recommended by the European Working Group on Sarcopenia in Older People (EWGSOP, 2010; EWGSOP2, 2018) and the Foundation of the National Institutes of Health (FNIH) and analyse the relationship between sarcopenia and body adiposity in adult renal transplant recipients (RTR). This was a cross-sectional study of adult RTR (BMI ≥ 18·5 kg/m2). Body composition was evaluated by dual-energy X-ray absorptiometry (DXA) and anthropometry. Glomerular filtration rate was estimated (eGFR) by CKD-Epidemiology Collaboration equation. The prevalence of sarcopenia in adult RTR (n 185; 57 % men, 50 (se 0·82) years and eGFR 55·80 (se 1·52) ml/min) was 7 % (FNIH), 11 % (EWGSOP2) and 17 % (EWGSOP). Low muscle mass, muscle function and physical performance affected, respectively, up to 28, 46 and 10 % of the participants. According to EWGSOP and EWGSOP2, body adiposity evaluated by anthropometry and DXA (percentage trunk fat) was lower in participants with sarcopenia. Conversely, according to the FNIH criteria, RTR with sarcopenia presented higher waist:height ratio. The present study suggests that adult RTR sarcopenia prevalence varies according to the diagnostic criteria; low muscle mass, low muscle function and low physical performance are common conditions; the association of body adiposity and sarcopenia depends on the criteria used to define this syndrome; and the FNIH criteria detected higher adiposity in individuals with sarcopenia.

High abdominal adiposity and low phase angle in overweight renal transplant recipients.

Obesity is associated with increased risk of cardiovascular disease (CVD). Body mass index (BMI) is the most used parameter for obesity screening. However, the evaluation of CVD risk in overweight individuals should include the assessment of body fat distribution and body composition. Renal transplant recipients (RTR) have a high CVD risk and frequently present weight gain and loss of lean mass. The aim of this study was to evaluate body fat distribution and body composition in overweight RTR. This cross-sectional study was conducted with 86 RTR and 86 hypertensive individuals (comparison group, CG) presenting BMI 25-35 Kg/m2 and 45-70 years. Anthropometric evaluation included BMI, waist circumference, waist-to-height ratio, and a body shape index. Body composition was evaluated with bioelectrical impedance analysis (BIA). Glomerular filtration rate was estimated (eGFR) by CKD-EPI equation. RTR group (RTRG) and CG presented similar age and BMI. RTRG when compared to CG presented lower percentage of women and eGFR; higher central adiposity; and lower values of reactance, intracellular water, body cell mass and phase angle, more consistently observed in women. This study suggests that overweight RTR present higher abdominal adiposity and impairment in BIA parameters that are sensitive indicators of impaired membrane integrity, water distribution, and body cell mass.

Obstructive sleep apnea in non-dialyzed chronic kidney disease patients: Association with body adiposity and sarcopenia.

OBJECTIVES: Obstructive sleep apnea (OSA) is a risk factor for cardiovascular disease (CVD), the main cause of mortality in chronic kidney disease (CKD). Although the prevalence of OSA in patients with CKD has not been established, a few studies suggest that it is higher than in the general population, potentially increasing the risk for CVD. Obesity increases the risk, whereas sarcopenia has been suggested as a consequence of OSA in the general population. To our knowledge, these associations have not been adequately evaluated in patients with CKD. The aim of this study was to evaluate OSA frequency and its association with total and upper body adiposity and sarcopenia in non-dialyzed CKD patients. METHODS: This cross-sectional study included 73 patients with stages 3b-4 CKD (42 men, 62.9 ± 1.1 y of age). Glomerular filtration rate was estimated by the CKD-Epidemiology Collaboration equation. Patients were assessed for OSA by Watch-PAT200 (apnea-hypopnea index ≥5 events hourly; Itamar Medical), total body adiposity by dual-energy x-ray absorptiometry (DXA) and body mass index (BMI), upper body adiposity by anthropometric parameters and by trunk and visceral fat by DXA, and sarcopenia. RESULTS: OSA frequency was 67% (N = 49). Both total and upper body adiposity were associated with the presence and severity of OSA. In non-obese patients (BMI <30 kg/m2), upper body obesity increased significantly the frequency of OSA. OSA association with sarcopenia was blunted when BMI was included in regression model. CONCLUSIONS: Results from the present study suggest that in non-dialyzed CKD patients OSA is very common and associated with total and upper body obesity, but not with sarcopenia.