Hidden Obesity in Dialysis Patients: Clinical Implications

Analyzing Neck Circumference as a Tool for Evaluating Overweight and Obesity in Chinese Adolescents

Overweight and obesity at an early age are important criteria for predicting chronic diseases. Each anthropometric method available to assess obesity has its limitations. Recently, neck circumference (NC) has received greater attention as a new evaluation index. This study aimed to investigate the relationship between NC and overweight in Chinese Yi adolescents. A total of 647 Chinese Yi male and female students, aged 13-18 years, were randomly selected from a junior high school and a senior middle school in Leshan, Sichuan Province of China. The measurement indexes included height, weight, waist circumference (WC), and NC, and clinical information was collected by trained physicians. The neck cutoff values were determined through the receiver operating characteristic (ROC) curve and the area under the curve (AUC). The correlation among NC, body mass index (BMI), and WC was determined by Pearson's correlation coefficient. The ROC analysis revealed that the AUC values were 0.79-0.95 for boys and 0.83-0.91 for girls. The correlation among NC, BMI, and WC in obese boys and girls was higher than 0.70 in both genders. In addition, the NC cutoff values of high BMI ranged from 31.0 cm to 36.1 cm for boys and 31.2 cm to 34.5 cm for girls, respectively. There was a significant positive correlation between NC and obesity in Chinese Yi adolescents. The NC can be used as an additional index to predict the obesity of Chinese Yi adolescents.

Significance of Adipose Tissue Maintenance in Patients Undergoing Hemodialysis

In the general population, obesity is known to be associated with adverse outcomes, including mortality. In contrast, high body mass index (BMI) may provide a survival advantage for hemodialysis patients, which is known as the obesity paradox. Although BMI is the most commonly used measure for the assessment of obesity, it does not distinguish between fat and lean mass. Fat mass is considered to serve as an energy reserve against a catabolic condition, while the capacity to survive starvation is also thought to be dependent on its amount. Thus, fat mass is used as a nutritional marker. For example, improvement of nutritional status by nutritional intervention or initiation of hemodialysis is associated with an increase in fat mass. Several studies have shown that higher levels of fat mass were associated with better survival in hemodialysis patients. Based on body distribution, fat mass is classified into subcutaneous and visceral fat. Visceral fat is metabolically more active and associated with metabolic abnormalities and inflammation, and it is thus considered to be a risk factor for cardiovascular disease and mortality. On the other hand, subcutaneous fat has not been consistently linked to adverse phenomena and may reflect nutritional status as a type of energy storage. Visceral and subcutaneous adipose tissues have different metabolic and inflammatory characteristics and may have opposing influences on various outcomes, including mortality. Results showing an association between increased subcutaneous fat and better survival, along with other conditions, such as cancer or cirrhosis, in hemodialysis patients have been reported. This evidence suggests that fat mass distribution (i.e., visceral fat and subcutaneous fat) plays a more important role for these beneficial effects in hemodialysis patients.

Sarcopenic Obesity in Chronic Kidney Disease: Challenges in Diagnosis Using Different Diagnostic Criteria

OBJECTIVES

Obesity, muscle impairment (low muscle mass or strength), and sarcopenic obesity are present in chronic kidney disease (CKD) and are associated with worse clinical prognosis. However, the various existing definitions for these conditions make the diagnosis variable. The aim of the present study was to evaluate the agreement between diagnostic criteria for sarcopenic obesity and its components in CKD.

SUBJECT AND METHODS

267 patients with CKD were included in the study. We assessed body composition by dual-energy X-ray absorptiometry and muscle function by handgrip strength (HGS) and adiposity by body mass index (BMI), waist circumference (WC), fat mass index (FMI), and percentage of FM. Diagnosis of muscle impairment was made by HGS, appendicular lean mass (ALM), and ALM index; obesity by BMI, WC, FMI, and %FM, and sarcopenic obesity was diagnosed by concomitant presence of muscle impairment and obesity.

RESULTS

Prevalence of muscle impairment varied from 11 to 50%, higher when low muscle mass criteria were used. Prevalence of obesity varied from 26 to 62%, higher when WC and %FM criteria were used. Prevalence of sarcopenic obesity varied from 2 to 23%. Women were more affected by sarcopenic obesity. Muscle impairment and sarcopenic obesity were more prevalent among patients on hemodialysis and obesity among nondialysis-dependent and kidney transplant patients. The agreement was poor between muscle mass and strength criteria; substantial between FMI, BMI, and %FM and fair between WC and the other measures; for sarcopenic obesity, it varied from poor to almost perfect.

CONCLUSION

Significant differences were found among the various diagnostic criteria that are used in the diagnosis of sarcopenic obesity. Our results highlight the need for standardization in the diagnosis of sarcopenic obesity.

Bed-side measures for diagnosis of low muscle mass, sarcopenia, obesity, and sarcopenic obesity in patients with chronic kidney disease under non-dialysis-dependent, dialysis dependent and kidney transplant therapy

Muscle depletion and sarcopenic obesity are related to a higher morbimortality risk in chronic kidney disease (CKD). We evaluated bed-side measures/indexes associated with low muscle mass, sarcopenia, obesity, and sarcopenic obesity in CKD and proposed cutoffs for each parameter. Sarcopenia was diagnosed according to the European Working Group on Sarcopenia in Older People revised consensus applying dual energy X-ray absorptiometry (DXA) and hand grip strength (HGS), and obesity according to the International Society for Clinical Densitometry. Anthropometric parameters including calf (CC) and waist (WC) circumferences and WC/height (WC/H); bioelectrical impedance data including appendicular fat free mass (AFFM) and fat mass index (FMI) were assessed. ROC analysis and area under the curve (AUC) were applied for performance analyses. AFFM and CC presented the best performances for low muscle mass diagnosis-AFFM AUC for women was 0.96 and for men, 0.94, and CC AUC for women was 0.89 and for men, 0.85. FMI and WC/H were the best parameters for obesity diagnosis-FMI AUC for women was 0.99 and for men, 0.96, and WC/H AUC for women was 0.94 and for men, 0.95. The cutoffs (sensibility and specificity, respectively) for women were AFFM≤15.87 (90%; 96%), CC≤35.5 (76%; 94%), FMI>12.58 (100%; 93%), and WC/H>0.66 (91%; 84%); and for men, AFFM≤21.43 (98%; 84%), CC≤37 (88%; 69%), FMI>8.82 (93%; 88%), and WC/H>0.60 (95%; 80%). Sensibility and specificity for sarcopenia diagnosis were for AFFM+HGS in women 85% and 99% and in men, 100% and 99%; for CC+HGS in women 85% and 99% and in men, 100% and 100%; and for sarcopenic obesity were for FMI+AFFM in women 75% and 97% and in men, 75% and 95%. The tested bed-side measures/indexes presented excellent performance.

Comparison between dual-energy x-ray absorptiometry and bioelectrical impedance for body composition measurements in adults with chronic kidney disease: A cross-sectional, longitudinal, multi-treatment analysis

OBJECTIVE

The aim of this study was to evaluate the agreement between bioelectrical impedance spectroscopy (BIS) and dual-energy x-ray absorptiometry (DXA) for assessment of body composition in patients with chronic kidney disease (CKD).

METHODS

We performed cross-sectional and prospective analyses by DXA and BIS in whole body (BISWB) and segmental (BISSEG) protocols in CKD non-dialysis-dependent (n = 81), hemodialysis (n = 83), peritoneal dialysis (n = 24), and renal transplantation (n = 80) patients. Intraclass correlation coefficient (ICC) and Bland-Altman plots were evaluated. Linear regression analysis was performed for bias assessment and development of equations. Receiver operating characteristics curve was constructed for diagnosis of inadequate error tolerance (DXA - BIS >±2kg).

RESULTS

The agreement with DXA was greater for BISWB than BISSEG; for fat mass (FM; ICC men = 0.894; women = 0.931) than fat-free mass (FFM; ICC men = 0.566; women = 0.525), with greater bias for FFM as muscle increases and for FM in body fat extremes. The agreement was lower for body change analysis (ICC FFM men = 0.196; women = 0.495; ICC FM men = 0.465; women = 0.582). The ratio of extra- to intracellular water (ECW/ICW), body mass index, fat mass index, waist circumference, resistance, and reactance interfered in bias between methods. An ECW/ICW cutoff point of ≥0.7250 for inadequate error tolerance was determined. New prediction equations for FFM (r² = 0.913) and FM (r² = 0.887) presented adequate error tolerance in 55% and 63% compared with 30% and 39% of the original equation, respectively.

CONCLUSION

For body composition evaluation in patients with CKD, BIS applied using the whole body protocol, in normal hydration patients with CKD is as reliable as DXA; BIS must be used with caution in overhydration patients with ECW/ICW ≥ 0.7250. The newly developed equations are indicated for greater precision.

Obesity in kidney transplantation

The prevalence of obesity among patients with chronic kidney disease continues to increase as a reflection of the trend observed in the general population. Factors affecting the access to the waiting list and the transplantability of this specific population will be analysed. From observational studies, kidney transplantation in obese patients carries an increased risk of surgical complications compared to the nonobese population; therefore, many centres have been reluctant to proceed with transplantation, despite this treatment modality confers a survival advantage over dialysis. As a consequence, obese patients continue to face decreased access to the waiting list, with a lower likelihood of being transplanted and higher waiting times when compared to the nonobese candidates. In this review will be described the current strategies for treatment of obesity in different settings (pretransplant, at transplant and post-transplant). Obesity represents a risk factor for surgical complications but not a contraindication for kidney transplantation; outcomes could be greatly improved with its multidisciplinary and multimodal treatment. The modern technology with minimally invasive techniques, mainly using robotic platform, allows a reduction in the surgical complications rate, with graft and patient survival rates comparable to the nonobese counterpart.

The obesity paradox: A further consideration in dialysis patients

Several epidemiological cohorts have demonstrated that higher body mass index (BMI) is associated with lower mortality risk among patients receiving hemodialysis. However, BMI may be an inaccurate indicator of nutritional status among dialysis patients because it does not differentiate between muscle and fat mass or provide information about body fat distribution. More sophisticated methods of body composition analysis are therefore required to address the question of which component is associated with greater survival. Recent evidence has also shown that changes in body weight and body composition are more strongly associated with mortality in dialysis patients than measurement of BMI at a single time point. Given that obesity is common among the dialysis population, weight loss interventions are encouraged for obese dialysis patients who are on a transplant waiting list in order to increase the access for transplantation.

Obesity and listing for renal transplantation: weighing the evidence for a growing problem

A 56-year-old female patient was referred to the transplant assessment clinic in July 2016. She started haemodialysis in 2012 for renal failure due to urinary tract infections. She is doing very well on dialysis and has an excellent exercise tolerance without shortness of breath or angina. She has had no infections since starting dialysis and no other comorbidity, except well-controlled hypertension and hyperparathyroidism requiring treatment with cinacalcet. Clinical examination is essentially normal except for truncal obesity with height 167 cm and weight 121 kg, giving her a body mass index of 43.4. Can she be listed for a renal transplant? If not, which target weight should be given to the patient before she can be transplant listed? Which interventions, if any, should be recommended to achieve weight loss?