Low Body Mass Index in Kidney Transplant Recipients: Risk or Advantage for Long-Term Graft Function?

Why protein-energy wasting leads to faster progression of chronic kidney disease

PURPOSE OF REVIEW

Protein-energy wasting (PEW) is increasingly more prevalent as chronic kidney disease (CKD) progresses to more advanced stages. There is a global recognition of the importance of preventing and mitigating PEW in the CKD population not on dialysis given the goal of extending dialysis-free time and delaying dialysis initiation and growing evidence of the clinical consequences of PEW which include the risk of death, hospitalization and clinical conditions such as infections. We reviewed the association of PEW and the malnutrition characteristics indicative of PEW on CKD progression.

RECENT FINDINGS

Studies show the association between low serum albumin levels, low BMI, and diets with inadequate dietary energy and protein intake and CKD progression. Limited studies suggest low muscle mass impacts CKD progression. Optimizing nutrition by dietary management, including a moderately low protein (0.6-0.8 g/kg/day) and plant-based (>50% of protein source, known as PLADO) diet and as needed with supplementation [e.g. during acute kidney injury (AKI) event] administrated orally, enterally, or parenterally are the basis for the prevention and treatment of PEW in CKD and delaying CKD progression. Furthermore, other therapeutic methods such as treating or avoiding comorbidities and AKI, ensuring appropriate exercise and incremental transition to dialysis treatment may help ameliorate and prevent PEW development in CKD patients.

SUMMARY

Using tailored precision nutrition approaches and nutritional supplementation with or without other beneficial strategies may help prevent and treat PEW and its consequent occurrence of CKD progression.

Underweight status and development of end-stage kidney disease: A nationwide population-based study

BACKGROUND

Underweight status increases the risk of cardiovascular disease and mortality in the general population. However, whether underweight status is associated with an increased risk of developing end-stage kidney disease is unknown.

METHODS

A total of 9 845 420 participants aged ≥20 years who underwent health checkups were identified from the Korean National Health Insurance Service database and analysed. Individuals with underweight (body mass index [BMI] < 18.5 kg/m2 ) and obesity (BMI ≥ 25 kg/m2 ) were categorized according to the World Health Organization recommendations for Asian populations.

RESULTS

During a mean follow-up period of 9.2 ± 1.1 years, 26 406 participants were diagnosed with end-stage kidney disease. After fully adjusting for other potential predictors, the moderate to severe underweight group (<17 kg/m2 ) had a significantly higher risk of end-stage kidney disease than that of the reference (normal) weight group (adjusted hazard ratio, 1.563; 95% confidence interval, 1.337-1.828), and competing risk analysis to address the competing risk of death also showed the similar results (adjusted hazard ratio, 1.228; 95% confidence interval, 1.042-1.448). Compared with that of the reference BMI group (24-25 kg/m2 ), the adjusted hazard ratios for end-stage kidney disease increased as the BMI decreased by 1 kg/m2 . In the sensitivity analysis, sustained underweight status or progression to underweight status over two repeated health checkups, when compared with normal weight status, had a higher hazard ratio for end-stage kidney disease.

CONCLUSIONS

Underweight status is associated with an increased risk of end-stage kidney disease, and this association gradually strengthens as BMI decreases.

Poor kidney graft survival in anorexia nervosa patients

BACKGROUND

Anorexia nervosa is a condition associated with poor outcomes in a variety of circumstances such as recurrence of eating disorders, psychiatric disorders, and organ damage.

OBJECTIVE

In the present study, we first sought to determine the 5-year kidney graft survival in patients with anorexia nervosa and then to evaluate the BMI course and medical complications.

METHODS

In this multicenter, retrospective, case-control study, we analyzed the impact of anorexia nervosa on graft outcomes compared to transplant recipients with low or normal BMI.

RESULTS

We enrolled 137 women in this study: 19 with anorexia nervosa, 59 with low BMI (BMI < 18.5 kg/m²), and 59 with normal BMI (18.5-24.9 kg/m²). Anorexia nervosa was significantly associated with lower graft survival compared to either of the other groups (hazard ratio 5.5 [95% CI 3.4-8.9], p = 0.005); there was no difference in graft survival between patients with low or normal BMI. Cardiovascular complications were more frequent in the anorexia nervosa group (37%) than in patients with low (6%) or normal BMI (7%) (p = 0.001).

CONCLUSION

We conclude that patients with anorexia nervosa should be considered a high-risk group.

LEVEL OF EVIDENCE

Level III, evidence obtained from well-designed cohort or case-control analytic studies.

Body mass index, weight-adjusted immunosuppression and the risk of acute rejection and infection after kidney transplantation: a cohort study

BACKGROUND

Body mass index (BMI) is associated with patient outcomes after kidney transplantation. We hypothesized that immunosuppression (IS) dosing is a contributing factor.

METHODS

Using Australia and New Zealand Dialysis and Transplant registry data, we included all adult kidney-only transplant recipients over 2000-14 treated with prednisolone, mycophenolate and tacrolimus/cyclosporin (n = 7919). The exposure was BMI and the outcomes were time to: (i) acute rejection, (ii) fatal infection, (iii) cancer and (iv) graft; and (v) patient survival. We modelled BMI and IS dosing (in quartiles) as time-varying covariates in extended Cox models.

RESULTS

Compared with a BMI of 25 kg/m2, a BMI of 35 was associated with acute rejection after adjusting for demographics and comorbidities [adjusted hazard ratio (aHR) = 1.29, 95% confidence interval (CI) 1.12-1.49]. This association virtually disappeared after correcting for IS (aHR = 1.09, 95% CI 0.93-1.29). A BMI of 35 was non-significantly associated with fewer fatal infections (aHR = 0.91, 95% CI 0.66-1.25), but this reversed after adjusting for IS (aHR = 1.54, 95% CI 1.03-2.28). Results for cancer were not significantly altered after adjusting for IS. Results for lower BMI were similarly not significantly altered though generally associated with worse outcomes.

CONCLUSIONS

Our findings show that the associations between high BMI, acute rejection and fatal infection after kidney transplantation were significantly altered after correcting for IS suggesting that relative under-dosing of obese patients may partially explain these associations.

Effect of BMI on allograft function and survival in pediatric renal transplant recipients

OBJECTIVE

To determine whether pre-transplant body mass index (BMI) affects renal allograft function and survival in pediatric renal transplant recipients.

STUDY DESIGN

This is a retrospective cohort study using the Organ Procurement and Transplantation Network data from 2000 to 2013 to compare time to total allograft loss (allograft failure or death), prevalence of delayed graft function, prevalence of acute rejection, and estimated glomerular filtration rate (eGFR) post-transplant in pediatric renal transplant recipients categorized by BMI z-score.

RESULTS

A total of 8804 kidney transplant recipients met our inclusion criteria, and of those, 6% were underweight, 14% were overweight, and 17% were obese pre-transplant. The adjusted hazard ratio (HR) for allograft failure was significantly higher for obese recipients compared to normal weight recipients (HR 1.25, 95% CI 1.1, 1.42); for every 1 point increase in BMI z-score, there was a 7% increased hazard of allograft failure (HR 1.07; 95% CI 1.03-1.1, p < 0.001). The prevalence of delayed graft function and acute rejection increased with higher BMI z-score category; however, this difference did not reach statistical significance. eGFR at 1 and 5 years post-transplant decreased with higher BMI z-score although it was only statistically significant at 1 year.

CONCLUSIONS

Obesity is prevalent in pediatric renal transplant recipients, and obese, but not overweight or underweight, pediatric renal transplant recipients have an increased risk of allograft failure. Implementation of effective obesity interventions in pediatric renal transplant recipients is of critical importance to improve longevity of the renal allograft.

Low plasma homoarginine concentration is associated with high rates of all-cause mortality in renal transplant recipients

In renal transplant recipients (RTR), we recently found that low urinary excretion of homoarginine (hArg) is associated with mortality and graft failure. However, it is not known whether such prospective associations also hold true for plasma concentrations of hArg. In the present study, we therefore determined plasma concentrations of hArg in the same cohort, i.e. in 687 RTR (functioning graft ≥1 year), and in 140 healthy donors, before and after kidney donation. Plasma hArg concentrations were significantly lower in RTR compared to healthy controls [1.24 (0.95-1.63) µM vs. 1.58 (1.31-2.03) µM, P < 0.001], and kidney donation resulted in a decrease in plasma hArg concentration to 1.41 (1.10-1.81) µM (P < 0.001). In RTR, multivariable linear regression analysis revealed BMI (β = 0.124), heart rate (β = -0.091), pre-emptive transplantation (β = 0.078), antidiabetic medication (β = -0.091), eGFR (β = 0.272), plasma PTH (β = -0.098), uric acid (β = 0.137), alkaline phosphatase (β = -0.100), HDL (β = -0.111), NT-pro-BNP (β = -0.166), and urinary urea excretion (β = 0.139) as main determinants of plasma hArg (all P < 0.05). In RTR, plasma hArg concentration was inversely associated with all-cause [hazard ratio (HR) 0.59 (95% CI 0.50-0.70), P < 0.001] and cardiovascular mortality [HR 0.50 (0.39-0.66), P < 0.001], both expressed per standard deviation change in log-transformed hArg, independent of potential confounders. To conclude, our results suggest that the kidney is a major hArg production site and an important modulator of hArg homeostasis in the renal and cardiovascular systems. Moreover, low plasma hArg is independently associated with increased risk of cardiovascular mortality in RTR, which corroborates the cardiovascular importance of preserving kidney function after transplantation.

The association between underweight and the development of albuminuria is different between sexes in relatively healthy Korean subjects

BACKGROUND

There are limited data on the association between underweight and albuminuria. The aim of this study is to verify the effect of underweight on the development of albuminuria.

METHODS

Participants who underwent two health check-ups with a 2-year interval at a tertiary hospital in Korea between 2002 and 2009 were studied. After exclusion of participants with estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2) or dipstick albuminuria ≥1+ at the first check-up, 53 876 participants were enrolled. We measured the incidence of albuminuria at the second check-up and calculated the odds ratio (OR) for the development of albuminuria according to body mass index (BMI).

RESULTS

After 2 years, 746 cases of incident albuminuria were observed among 53 876 participants. The effect of BMI on the development of albuminuria was modified by sex in a multivariate logistic model with adjustment for age, diabetes, hypertension, dyslipidaemia, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, uric acid, eGFR, current smoking status and alcohol intake (P-value for interaction <0.001). Compared with participants in the normal weight range (BMI, 18.5-22.9), the ORs for incident albuminuria were 1.93 [95% confidence interval (CI), 1.35-2.76; P ≤ 0.001], 1.19 (0.84-1.67; P = 0.329) and 0.71 (0.43-1.17; P = 0.177) in underweight (BMI, <18.5), overweight (BMI, 23.0-24.9) and obese (BMI, ≥25) women. However, the ORs were 0.9 (95% CI, 0.39-2.05; P = 0.794), 1.08 (0.84-1.38; P = 0.567) and 1.38 (1.09-1.75; P = 0.007) for each corresponding group of men.

CONCLUSIONS

Underweight was significantly associated with the development of albuminuria after 2 years in relatively healthy Korean females, but this relationship was not significant in males. This study suggests the need for more studies on the role of underweight in renal injury in men and women.

Evaluation of nutrient intake in early post kidney transplant recipients

The purpose of our study was to evaluate the dietary intake of kidney transplant recipients (KTRs) and assess oral intake related nutrition problems. Fifty patients who had undergone kidney transplantation were included: 24 males, 26 females. The mean age was 46.8 ± 11.2 years, height was 161.3 ± 8.3 cm, and body weight was 60.5 ± 8.7 kg. We conducted nutrition education based on the diet guideline for KTRs (energy 32 kcal/kg of ideal body weight [IBW], protein 1.3 g/kg of IBW) and neutropenic diet guideline before discharge. Dietary intake of the patients at 1 month after transplantation was investigated by 3-day food records. Body weight and laboratory values for nutritional status and graft function were also collected. Body weight was significantly decreased from admission to discharge. Body weight from discharge to 1 month and 3 months after transplantation was increased but was not significant. Biochemical measurements were generally improved but the number of patients with hypophosphatemia increased. The daily dietary intake of energy and protein was adequate (33.1 kcal/kg, 1.5 g/kg, respectively). However, the dietary intake of calcium, folate, and vitamin C did not meet the Korean Recommended Nutrient Intake of vitamins and minerals (86.8%, 62.4%, and 88.0%, respectively). Patients with low intake of calcium, folate, and vitamin C presented low intake in milk and dairy products, vegetables, and fruits, and these foods were related to restricted food items in neutropenic diet. More attention should be paid on improving quality of diet, and reconsideration of present neutropenic diet guideline is necessary. These results can be used to establish evidence-based medical nutrition therapy guideline for KTRs.

Effect of obesity on the outcome of kidney transplantation: a 20-year follow-up

BACKGROUND

Cardiovascular disease is both a major threat to the life expectancy of kidney transplant recipients and an important determinant of late allograft loss. Obesity is an important risk factor for cardiovascular disease.

METHODS

We investigated the relation between both pretransplant and 1-year posttransplant body mass index (BMI) with patient and renal graft survival in a cohort of 1810 adult patients. Sixty-one percent of all patients were men; median age (interquartile range [IQR]) was 46 years (35-56 years); median (IQR) pretransplant BMI was 23.0 kg/m (20.8-25.6 kg/m); 1 year after transplantation, the median (IQR) BMI had increased 1.6 kg/m (0.3-3.2 kg/m) and median (IQR) follow-up time was 8.3 years (5.3-12.0 years). We categorized BMI as follows: less than or equal to 20, more than 20 to less than or equal to 25 (normal), more than 25 to less than or equal to 30, and more than 30 (obesity) kg/m.

RESULTS

Using a Cox proportional hazards model, after adjustment for cardiovascular risk factors, the relative risks (95% confidence intervals) of death and death-censored graft failure during all follow-up for pretransplant obesity compared with normal BMI were 1.22 (0.86-1.74) and 1.34 (1.02-1.77), respectively; for obesity 1 year after transplantation compared with normal BMI, it was 1.39 (1.05-1.86) and 1.39 (1.10-1.74), respectively; and for change in BMI (per 5 kg/m increment) during the first year after transplantation, it was 1.23 (1.01-1.50) and 1.18 (1.01-1.38), respectively.

CONCLUSIONS

One year posttransplant BMI and BMI increment are more strongly related to death and graft failure than pretransplant BMI among kidney transplant recipients. Patients with BMI more than 30 kg/m compared with a normal BMI have approximately 20% to 40% higher risk for death and graft failure.