|Year : 2018 | Volume
| Issue : 4 | Page : 101-105
Nutritional management of peritoneal dialysis patient
Mayoor Prabhu1, KS Nayak2
1 Consultant Nephrologist, Department of Nephrology, Kasturba Medical College, Mangalore, Karnataka, India
2 Consultant Nephrologist, Department of Nephrology, Deccan Hospital, Hyderabad, Telangana, India
|Date of Web Publication||19-Sep-2019|
Department of Nephrology, Kasturba Medical College, Mangalore, Karnataka
Source of Support: None, Conflict of Interest: None
Malnutrition inevitably accompanies chronic kidney disease and dialysis. Markers of malnutrition such as low-serum albumin have been shown to correlate independently with higher mortality in dialysis patients. Malnutrition is seen in both hemodialysis and peritoneal dialysis (PD) patients. Nutritional management of PD patients is challenging and vital to the patients' long-term survival and well-being. A multidisciplinary approach with a patient-centric plan is necessary to achieve long-term compliance and success. Consideration to cultural, economic, and medical issues is paramount to develop a workable plan, especially in a country as large and diverse as India. This article reviews nutritional management of PD patient.
Keywords: Chronic kidney disease, malnutrition, peritoneal dialysis, serum albumin
|How to cite this article:|
Prabhu M, Nayak K S. Nutritional management of peritoneal dialysis patient. J Renal Nutr Metab 2018;4:101-5
| Introduction|| |
Malnutrition inevitably accompanies chronic kidney disease (CKD) and dialysis. Markers of malnutrition such as low-serum albumin have been shown to correlate independently with higher mortality in dialysis patients. Malnutrition is seen in both hemodialysis (HD) and peritoneal dialysis (PD) patients. The incidence has been described at 10%–70% in HD and 18-51% in PD patients., The causes of malnutrition in dialysis patients can be manifold-dialysis factors, biochemical factors, gastrointestinal factors, miscellaneous factors, and low socioeconomic status. Miscellaneous factors include depression, multiple medications, recurrent hospitalizations, and underlying illness. Modality of dialysis also affects nutritional status. There are factors unique to each both PD and HD that may contribute to the overall malnutrition. In PD, loss of albumin in PD fluid may range from 5.5 to 11.8 g/day. In comparison, low-flux dialyzers account for amino acid losses of 5.6–7.1 g/day in HD patients. Thus, PD patients maintain lower serum albumin than age- and weight-controlled HD patients. Other causes responsible for hypoalbuminemia in PD patients include older age, etiology of renal failure, transport status, and chronic inflammation. Anorexia can result from distention due to fluid in the abdomen. Episodes of peritonitis can cause protein losses of up to 15 g/day. Overhydration and early satiety due to absorption of glucose from PD fluid can also be a cause of malnutrition in PD. Hospitalization of dialysis patients is estimated to lead to them missing up to 20% of their lunches and dinners, with calorie deficits of up to 3000 kcal/week. Other factors may ultimately impinge on dialysis patients' nutritional well-being. Blindness, amputations, dementia, depression, and stroke are some factors adding to the nutritional challenges. Disabilities are more in HD patients than in PD and are also more common in diabetics than nondiabetics. As the number of patients with diabetes on PD increased exponentially, malnutrition is also expected to increase with the same rate. Even though malnutrition is very common and strongly predicts an outcome, it is not thought to directly cause death. Rather, a combination of malnutrition, inflammation, and cardiovascular disease may be interrelated in dialysis., Serum levels of C-reactive protein (CRP) and interleukin-6 (IL-6, which is a pivotal pro-inflammatory cytokine involved in systemic inflammation) were found to be significantly elevated in malnourished HD and PD patients. As a marker of systemic inflammatory reaction, serum CRP is now regarded as the best predictor for the development of cardiovascular disease in the general population as well as in dialysis patients. These factors led to the proposal that malnutrition is characterized as Type 1 and Type 2. Type 1 malnutrition is related to the uremic syndrome per se and can be corrected by adequate dialysis. It is characterized by a normal/low-serum albumin, absence of inflammation and comorbidity, low food intake, and decreased protein catabolism. Type 2 malnutrition is thought to be “cytokine-driven” and is clinically more severe, characterized by hypoalbuminemia, inflammation, comorbidity, and increased protein catabolism. Thus, it is clear that malnutrition and comorbidities play a major role in determining outcomes in patients on PD. Assessment and treatment of nutritional problems in PD may lead to overall better performance on PD, better quality of life, and increased longevity. Methods of assessment of nutritional status, the interpretation and limitations of the same, approaches toward the optimum treatment strategies, and future directions in the management of nutritional status in PD patients are dealt with.
| Global Perspective|| |
The prevalence of malnutrition in PD patients varies based on the method of assessment used. For unclear reasons, longitudinal studies have shown that after initiation on PD, following an initial improvement, nutritional status gradually declines.,, There is a clear association between malnutrition and poor outcome in PD patients, but the relevant studies, including the much-quoted CANUSA study, were based on Caucasian populations. It is not yet known whether the relationship is also applicable for Asian populations and whether Asian PD patients have distinct and unique nutritional issues compared to their Western counterparts. Furthermore, it is not clear whether the reported superior survival of Asian patients can be related to better preservation of nutritional status., There is a general feeling that the incidence of malnutrition is essentially similar in Western and Asian populations, but the incidence of severe malnutrition is lower in Asian populations.,,, Lesser activation of a systemic inflammatory reaction in Asian PD patients is suggested, and that circumstance may partially explain their lower incidence of malnutrition as compared with Western PD patients. Lesser incidence of metabolic acidosis in Asian patients has also been reported. It appears that correction of metabolic acidosis improves the nutritional status of Asian PD patients, which is consistent with the results from earlier reports in Western PD patients. Reported data indicate that dietary protein and energy intakes are not much different, although actual dietary intake of nutrients is independently influenced by the delivered dialysis dose and residual renal function (RRF) in Asian PD patients. The effect of peritoneal membrane transport characteristics on the long-term nutritional status remains controversial. Establishing a relationship between dialysis adequacy and nutritional status (and clinical outcome) would give nutrition a central role and thus have important therapeutic implications. Important nutritional issues that need further investigation in Asian PD patients include determining daily diet requirements for the maintenance of a positive nitrogen balance, establishing an optimum method to assess nutritional status, and developing preventive and therapeutic strategies to manage malnutrition.
| Indian Scenario|| |
The lack of a renal registry system in India prevents an exact estimation of the incidence of renal failure and end-stage renal disease in India. Estimates suggest that an average of 160,000 new patients require dialysis every year in India. Several problems mar the optimum use of PD in our patients. An initial prescription is usually limited to three exchanges of 2-L bags. Most patients are unable to afford four exchanges or the use of newer/biocompatible solutions. Currently, about 6000 patients are receiving PD in the country. Malnutrition in Indian patients is often severe and multifactorial. Reasons include late initiation of PD, protein restriction in the predialysis period, intercurrent infections, comorbidity, and dietary factors. Patients invariably do not comply to recommended dietary intakes. The mean age of our continuous ambulatory PD (CAPD) patients is lower than that of PD patients in Western countries, and most of our PD patients are malnourished at PD initiation. Comorbidities may also be different in Indian PD patients. Vegetarianism is very common in India, which means that patients do not get animal-source protein in their diet. Dietary habits in India are complex with many patients being pure vegetarians, some who take meat occasionally and some who are take meat regularly (nonvegetarians). This makes nutritional assessment and management difficult. Data on Indian patients' nutritional status are scant. A recent trial showed that malnutrition at the initiation of PD was predictive of higher incidence of peritonitis. Patients were categorized into malnourished or well-nourished groups on the basis of subjective global assessment (SGA) scores. Malnourished patients experienced significantly more peritonitis episodes (1 vs. 0.2 annually) than did patients with a normal nutritional status. On univariate analysis, SGA, nutritional risk index, serum albumin, and daily calorie intake were significantly associated with peritonitis. On multivariate regression analysis, only SGA was a significant predictor of peritonitis. Peritonitis-free survival was better in patients showing normal nutrition than showing malnutrition. Indian PD patients are thought to consistently fail to achieve National Kidney Foundation-Kidney Disease Outcomes Quality Initiative-recommended calorie and protein intake, which was confirmed in some Indian studies. There is an overall paucity of good data from India. Assessment of nutritional status and the management of malnutrition, all remain suboptimal at present.
| Assessment of Nutritional Status in Peritoneal Dialysis Patients|| |
An ideal assessment of the nutritional status of a patient draws from a detailed history and clinical examination including anthropometry and biochemical tests. There is no ideal and 100% effective method available at present. Current strategies of evaluating nutritional status vary from center to center and depend on many factors including economic considerations. In a country like India, it is impossible to perform too frequent and cumbersome investigations, especially when they are expensive. The different available tools for nutritional assessment are discussed here.
| Subjective Global Assessment|| |
This is probably the most widely used method of nutritional assessment. It is simple and inexpensive. It is based on the clinician's ability to make an assessment of the overall nutritional status based on a medical history and clinical examination, to derive a final score. In general, 60% of the clinician's rating of the patient is based on the results of the medical history and 40% on the physical examination. The clinician rates each medical history and physical examination parameters as either an A, B, or C. Although originally used to categorize surgical patients, this nutritional classification system has been shown to be a reliable nutritional assessment tool for dialysis patients., SGA is limited by the very fact that it is subjective and may not be entirely reproducible due to observer variability. In addition, its ability to detect small variations in nutritional status is limited. One parameter, the degree of anorexia, has been reported to be a strong predictor of mortality in HD patients.
| Serum Albumin and Prealbumin|| |
Serum albumin has been, by far, the most commonly used marker of nutrition status in CKD patients, and it is a powerful predictor of mortality in PD patients. However, serum albumin as a marker of malnutrition has several caveats. The low-serum albumin level observed in PD patients may reflect mostly the acute-phase response and resulting albumin losses in dialysate and urine and only to a lesser extent, poor nutrition status. The patient's clinical status must be examined when evaluating the changes in the serum albumin concentration, which is weakly and inversely correlated with serum acute-phase proteins. Prealbumin is thought to be a better marker than serum albumin due to its shorter half-life and better correlation to the nutritional status. However, prealbumin is also a negative acute-phase reactant. Furthermore, the prealbumin levels are related to the RRF., Hence, both these markers may not be the ideal reflection of nutritional status.
| Serum Transferrin|| |
Serum transferrin, though initially thought to reflect nutritional status, is now not widely used. It is almost universally low in dialysis patients and reflects iron status predominantly.
| Protein Equivalent of Total Nitrogen Appearance|| |
The use of protein equivalent of total nitrogen appearance (nPNA) as an estimate of protein intake is simple to use in the clinical setting. nPNA approximates the daily protein intake (DPI) only when the patient is in nitrogen equilibrium or steady state. It will change in anabolic or catabolic situations and needs to be interpreted accordingly.
| Anthropometry and Handgrip Strength|| |
The anthropometric parameters that are generally assessed include body weight, height, skeletal frame size, skin-fold thickness, mid-arm muscle circumference, percentage of the body mass, that is fat, the percentage of usual body weight, the percentage of standard body weight, and the body mass index.,, These various measures provide different information concerning body composition, and it is therefore advantageous to measure more than one of these parameters. Moreover, these tests are cheap and easy to perform. There is a focus on handgrip strength as a nutritional assessment tool, as it has been demonstrated to predict the mortality on PD patients. It is recommended to use some of these tests singly or in combination for the diagnosis of malnutrition and also for the follow-up of patients.
| Body Composition Measurements|| |
- Dual-energy X-ray absorptiometry (DEXA) – This is considered superior to other currently available techniques. With DEXA, bone mineral, fat mass, and lean body mass (LBM) distribution are estimated directly. However, the assessment of LBM by DEXA is subject to flaws because it assumes that 72% of the LBM compartment is water. Given that PD patients can exhibit abnormal hydration status, DEXA might not be a very precise method for assessing LBM in dialyzed patients. Therefore, measurement of LBM by DEXA should be combined with the estimation of the extracellular fluid volume by the tracer-dilution technique It provides accurate data on body composition, which are superior to anthropometry, creatinine kinetics, and bioelectrical impedance,
- Bioimpedance analysis (BIA) – BIA is based on the measurement of resistance and reactance when a constant alternating electrical current is applied to a patient by empirical equations. However, BIA is highly influenced by hydration status. It is recommended that BIA be attempted only when the patient is at his edema free weight. Our own experience with the use of BIA in CAPD patients showed good results
- Creatinine kinetics – Creatinine kinetics is based on creatinine excretion in urine and dialysate. LBM estimated from creatinine kinetics depends on the creatinine content in the diet and the metabolic degradation of creatinine. Variations observed during repeated measures of LBM estimated using creatinine kinetics are unacceptably high. From the available tests, we recommend relying on a panel of nutritional markers rather than any one particular test. We recommend the assessment of nutritional status at least every 6 months. Ideally, body weight, serum albumin, SGA, protein intake as assessed from dietary recall or nPNA, and an assessment of protein stores and iron stores (serum transferrin) would be necessary. A prospective decline in nutritional status would prompt a detailed evaluation. A cost-effective but complete strategy for Indian patients would be a six monthly battery of tests that include serum albumin, serum transferrin saturation, SGA, and anthropometrics/handgrip strength. While inexpensive, these tests would enable the assessment of all necessary parameters.
| Nutritional Intervention Strategies|| |
It is important to individualize the strategies for each patient rather than slavishly adhere to guidelines or formulae. Considerations toward cost, palatability, culture, and comorbidity should be considered. We recommend using the services of a renal dietician in addition to the expertise of the treating physician. In consultation with the patient, a unique and exclusive plan is drawn up for each patient.
| Daily Protein Intake|| |
While a DPI of 1.3 g/kg/day is recommended, there is no conclusive evidence to show that lower protein intakes impact on nutritional status in PD. Some studies have shown that a DPI of 1.0–1.2 g/kg/day is adequate to maintain a positive nitrogen balance., We would recommend a DPI of >1.0 g/kg/day as sufficient if the patient has no declining trend in nutritional parameters. At a DPI of <0.9 g/kg/day, we would reassess the patients nutritional status. Our own experience with the use of 0.8 g/kg/day of protein, supplemented with keto-analogs 0.4 g/kg/day, when compared with a traditional protein diet of 1.2 g/kg/day showed that the keto-group had an improvement on parameters such as appetite, anthropometry, serum albumin, and a decrease in serum cholesterol and fasting blood sugar.
| Conclusions|| |
Nutritional management of PD patients is challenging and vital to the patients' long-term survival and well-being. A multidisciplinary approach with a patient-centric plan is necessary to achieve long-term compliance and success. Consideration to cultural, economic, and medical issues is paramount to develop a workable plan, especially in a country as large and diverse as India.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Joki N, Hase H, Tanaka Y, Takahashi Y, Saijyo T, Ishikawa H, et al.
Relationship between serum albumin level before initiating haemodialysis and angiographic severity of coronary atherosclerosis in end-stage renal disease patients. Nephrol Dial Transplant 2006;21:1633-9.
Bergström J, Lindholm B. Nutrition and adequacy of dialysis. How do hemodialysis and CAPD compare? Kidney Int Suppl 1993;40:S39-50.
Kopple JD. McCollum award lecture, 1996: Protein-energy malnutrition in maintenance dialysis patients. Am J Clin Nutr 1997;65:1544-57.
Hakim RM, Levin N. Malnutrition in hemodialysis patients. Am J Kidney Dis 1993;21:125-37.
Blumenkrantz MJ, Kopple JD, Moran JK, Coburn JW. Metabolic balance studies and dietary protein requirements in patients undergoing continuous ambulatory peritoneal dialysis. Kidney Int 1982;21:849-61.
Ikizler TA, Flakoll PJ, Parker RA, Hakim RM. Amino acid and albumin losses during hemodialysis. Kidney Int 1994;46:830-7.
Bannister DK, Acchiardo SR, Moore LW, Kraus AP Jr. Nutritional effects of peritonitis in continuous ambulatory peritoneal dialysis (CAPD) patients. J Am Diet Assoc 1987;87:53-6.
Sezer S, Tutal E, Arat Z, Akçay A, Celik H, Ozdemir FN, et al.
Peritoneal transport status influence on atherosclerosis/inflammation in CAPD patients. J Ren Nutr 2005;15:427-34.
Laville M, Fouque D. Nutritional aspects in hemodialysis. Kidney Int Suppl 2000;76:S133-9.
United States Department of Health and Human Services, Public Health Service, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Division of Kidney, Urologic, and Hematologic Diseases. USRDS 2007 Annual Data Report. Atlas of End-Stage Renal Disease in the United States. Bethesda: United States Renal Data System; 2007.
Bergström J, Lindholm B. Malnutrition, cardiac disease, and mortality: An integrated point of view. Am J Kidney Dis 1998;32:834-41.
Stenvinkel P, Heimbürger O, Lindholm B, Kaysen GA, Bergström J. Are there two types of malnutrition in chronic renal failure? Evidence for relationships between malnutrition, inflammation and atherosclerosis (MIA syndrome). Nephrol Dial Transplant 2000;15:953-60.
Wang T, Heimbürger O, Bergström J, Lindholm B. Nutritional problems in peritoneal dialysis: An overview. Perit Dial Int 1999;19 Suppl 2:S297-303.
Young GA, Kopple JD, Lindholm B, Vonesh EF, De Vecchi A, Scalamogna A, et al.
Nutritional assessment of continuous ambulatory peritoneal dialysis patients: An international study. Am J Kidney Dis 1991;17:462-71.
Davies SJ, Phillips L, Griffiths AM, Russell LH, Naish PF, Russell GI. What really happens to people on long-term peritoneal dialysis? Kidney Int 1998;54:2207-17.
Johansson AC, Samuelsson O, Haraldsson B, Bosaeus I, Attman PO. Body composition in patients treated with peritoneal dialysis. Nephrol Dial Transplant 1998;13:1511-7.
Churchill DN, Taylor DW, Keshaviah PR; The CANUSA Peritoneal Dialysis Study Group. Adequacy of dialysis and nutrition in continuous peritoneal dialysis: Association with clinical outcomes. J Am Soc Nephrol 1996;7:198-207.
Wong JS, Port FK, Hulbert-Shearon TE, Carroll CE, Wolfe RA, Agodoa LY, et al.
Survival advantage in Asian American end-stage renal disease patients. Kidney Int 1999;55:2515-23.
Held PJ, Brunner F, Odaka M, Garcia JR, Port FK, Gaylin DS. Five-year survival for endstage renal disease patients in the United States, Europe, and Japan, 1982 to 1987. Am J Kidney Dis 1990;15:451-7.
Chung SH, Na MH, Lee SH, Park SJ, Chu WS, Lee HB. Nutritional status of Korean peritoneal dialysis patients. Perit Dial Int 1999;19 Suppl 2:S517-22.
Kumano K, Kawaguchi Y. Multicenter cross-sectional study for dialysis dose and physician's subjective judgment in Japanese peritoneal dialysis patients. Group for the water and electrocyte balance study in CAPD. Am J Kidney Dis 2000;35:515-25.
Wang AY, Sea MM, Ip R, Law MC, Chow KM, Lui SF, et al.
Independent effects of residual renal function and dialysis adequacy on actual dietary protein, calorie, and other nutrient intake in patients on continuous ambulatory peritoneal dialysis. J Am Soc Nephrol 2001;12:2450-7.
Kang EW, Goo YS, Lee SC, Han SH, Yoon SY, Choi SR, et al
. Factors affecting malnutrition in continuous ambulatory peritoneal dialysis patients: A cross sectional study. Korean J Nephrol 2002;21:943-55.
Noh H, Lee SW, Kang SW, Shin SK, Choi KH, Lee HY, et al.
Serum C-reactive protein: A predictor of mortality in continuous ambulatory peritoneal dialysis patients. Perit Dial Int 1998;18:387-94.
Kang DH, Lee R, Lee HY, Han DS, Cho EY, Lee CH, et al.
Metabolic acidosis and composite nutritional index (CNI) in CAPD patients. Clin Nephrol 2000;53:124-31.
Mak SK, Wong PN, Lo KY, Tong GM, Fung LH, Wong AK. Randomized prospective study of the effect of increased dialytic dose on nutritional and clinical outcome in continuous ambulatory peritoneal dialysis patients. Am J Kidney Dis 2000;36:105-14.
Oreopoulos DG. The optimization of continuous ambulatory peritoneal dialysis. Kidney Int 1999;55:1131-49.
Modi GK, Jha V. The incidence of end-stage renal disease in India: A population-based study. Kidney Int 2006;70:2131-3.
Abraham G, Mathew M, Gopalakrishnan P, Sankarasubbaiyan S, Shroff S. Are three exchanges suitable for Asian patients on peritoneal dialysis? Perit Dial Int 2003;23 Suppl 2:S45-7.
Prasad N, Gupta A, Sinha A, Singh A, Sharma RK, Kumar A, et al.
Acomparison of outcomes between diabetic and nondiabetic CAPD patients in India. Perit Dial Int 2008;28:468-76.
Prasad N, Gupta A, Sinha A, Sharma RK, Kumar A, Kumar R. Changes in nutritional status on follow-up of an incident cohort of continuous ambulatory peritoneal dialysis patients. J Ren Nutr 2008;18:195-201.
Prasad N, Gupta A, Sharma RK, Sinha A, Kumar R. Impact of nutritional status on peritonitis in CAPD patients. Perit Dial Int 2007;27:42-7.
Enia G, Sicuso C, Alati G, Zoccali C. Subjective global assessment nutrition in dialysis patients. J Am Soc Nephrol 1991;1:323.
Kalantar-Zadeh K, Block G, McAllister CJ, Humphreys MH, Kopple JD. Appetite and inflammation, nutrition, anemia, and clinical outcome in hemodialysis patients. Am J Clin Nutr 2004;80:299-307.
Gabay C, Kushner I. Acute-phase proteins and other systemic responses to inflammation. N Engl J Med 1999;340:448-54.
Heimbürger O, Qureshi AR, Blaner WS, Berglund L, Stenvinkel P. Hand-grip muscle strength, lean body mass, and plasma proteins as markers of nutritional status in patients with chronic renal failure close to start of dialysis therapy. Am J Kidney Dis 2000;36:1213-25.
Jacob V, Marchant PR, Wild G, Brown CB, Moorhead PJ, el Nahas AM, et al.
Nutritional profile of continuous ambulatory peritoneal dialysis patients. Nephron 1995;71:16-22.
Woodrow G, Oldroyd B, Smith MA, Turney JH. Measurement of body composition in chronic renal failure: Comparison of skinfold anthropometry and bioelectrical impedance with dual energy X-ray absorptiometry. Eur J Clin Nutr 1996;50:295-301.
Jones CH, Newstead CG, Will EJ, Smye SW, Davison AM. Assessment of nutritional status in CAPD patients: Serum albumin is not a useful measure. Nephrol Dial Transplant 1997;12:1406-13.
Szeto CC, Kong J, Wu AK, Wong TY, Wang AY, Li PK, et al.
The role of lean body mass as a nutritional index in Chinese peritoneal dialysis patients – Comparison of creatinine kinetics method and anthropometric method. Perit Dial Int 2000;20:708-14.
Wang AY, Sea MM, Ho ZS, Lui SF, Li PK, Woo J. Evaluation of handgrip strength as a nutritional marker and prognostic indicator in peritoneal dialysis patients. Am J Clin Nutr 2005;81:79-86.
Borovnicar DJ, Wong KC, Kerr PG, Stroud DB, Xiong DW, Strauss BJ, et al.
Total body protein status assessed by different estimates of fat-free mass in adult peritoneal dialysis patients. Eur J Clin Nutr 1996;50:607-16.
Stenver DI, Gotfredsen A, Hilsted J, Nielsen B. Body composition in hemodialysis patients measured by dual-energy X-ray absorptiometry. Am J Nephrol 1995;15:105-10.
Brundavani V, Nayak KS, Vinny J, Fatima P, Subhramanyam SV, Sinoj K. A bioelectric impedance vector analysis (BIVA) for nutritional health assessment in CAPD patients – An Indian study. Perit Dial Int 2005;25:45.
Bhatla B, Moore H, Emerson P, Keshaviah P, Prowant B, Nolph KD, et al.
Lean body mass estimation by creatinine kinetics, bioimpedance, and dual energy X-ray absorptiometry in patients on continuous ambulatory peritoneal dialysis. ASAIO J 1995;41:M442-6.
Giordano C, De Santo NG, Pluvio M, Di Leo VA, Capodicasa G, Cirillo D, et al.
Protein requirement of patients on CAPD: A study on nitrogen balance. Int J Artif Organs 1980;3:11-4.
Brundavani V, Nayak KS, Vinny J, Fatima P, Kanchana D, Subhramanyam SV. Dietary protein quality evaluation: Ammonia acid score and relative protein digestibility of Indian renal diets. Perit Dial Int 2005;25:2.