Dietary Management of Early Chronic Kidney Disease
Fiona Byrne, Clinical Specialist Renal Dietitian, Cork University Hospital
Major Points: • CKD is becoming increasingly common due to our ageing population and a rising incidence of type 2 diabetes and hypertension. • CKD is a potent independent risk factor for cardiovascular disease. • Optimal management of the risk factors for cardiovascular disease also slows the progression of CKD. • Most patients with CKD will not progress to end stage kidney disease. • The majority of people with CKD will be managed in general practice. • Early CKD is described as stage 1-3.
Classification of CKD
The KDOQI Classification System described in 2002 is very widely used in the literature. From a dietary perspective, while it allows us to broadly describe dietary management at the different stages of CKD, individual assessment including biochemistry will dictate your care plan for individual patients. An international classification of CKD has identified 5 stages 1 (see Table 1).
The definition of chronic kidney disease has been simplified since the introduction of this classification system. It is now defined as the presence of kidney damage for a period greater than 3 months. An estimated or measured glomerular filtration rate of less than 60 ml/min/1.73m2 is considered abnormal for all adults. A rate of more than 60 ml/min/1.73m2 is considered abnormal if it is accompanied by abnormalities of urine sediment or abnormal results of imaging tests, or if the patient has had a kidney biopsy with documented abnormalities 2.
eGFR is a useful measure of renal function, calculated using serum creatinine, age, gender and race. It is a far superior test to serum creatinine, when trying to assess renal function as many elderly individuals have normal or mildly elevated serum creatinine though eGFR is markedly reduced.
eGFR can be interpreted as the percentage of normal kidney function such that an eGFR of 50 ml/minute/1.73m2 approximates 50% of normal kidney clearance 2.
eGFR: • May be available from your local laboratory • Can be calculated using a prediction chart if you have internet access at your clinic using an online calculator e.g. NKF website • Should NOT be used in patients with acute kidney failure and there are certain circumstances where eGFR may not be accurate e.g. patients less than 18 years of age, patients with advanced muscle wasting, patients with amputations, and in pregnancy.
What is early CKD?
Early CKD is described as stage 1-3.
How common is early CKD?
It is estimated that as many as 10% of the UK adult population have early CKD, of whom half will have stage 3. This increases with age to approximately 20% over 65 years and more than 30% over 80 years.3
What are the Consequences of CKD?
It has been estimated in the US that less than 2% of the CKD population progresses to renal replacement therapy (dialysis and transplantation) 4.
UK population studies have demonstrated that the risk of cardiovascular death in people with diagnosed CKD far outweighs the risk of disease progression 5. A retrospective cohort study found that only 4% of 1076 individuals progressed to end stage kidney disease over a 5.5 year follow-up period whilst 69% had died at the end of follow-up; the cause of death was cardiovascular in 46% of cases 6.
Goals of CKD therapy
To delay progression of renal failure, reduce overall cardiovascular risk and avoid complications 2.
1. Target Proven Risk Factors such as Hypertension and Diabetes Hypertension: Hypertension is both a cause of CKD and a complication of CKD, it can be difficult to control.
Irish CKD Guidelines 2: • Target blood pressure < 130/80 mmHg. Lower targets may be appropriate in patients with diabetes or proteinuria; • Low salt diet (< 100mmol (2.4 grams) sodium per day); • Angiotensin converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) as first choice AND increase to maximum tolerated dose; • Monitor serum creatinine and potassium during treatment; • Most patients will need > 2 medications for optimal control.
Diabetes Mellitus: Intensive blood glucose control significantly reduces the risk of developing microalbuminuria, macroalbuminuria and/or overt nephropathy in people with Type 1 and Type 2 diabetes . The ADVANCE study showed that in patients with type 2 diabetes a strategy of intensive glucose control, resulted in a 21% relative reduction in nephropathy 7.
Irish CKD Guidelines 2: • Target HbA1C < 7.0%; • ACE inhibitor or ARB as first choice in patients with hypertension and/or (micro) albuminuria and increase to maximum tolerated dose; • Target a reduction in proteinuria (< 100 mg/mmol); • Avoid use of metformin when eGFR < 60 ml/min.
2. Watch for Potential Complications Cardiovascular Complications: Attention to cardiovascular risk factors, especially the treatment of hypertension described above, remains the cornerstone of care to delay progression of chronic kidney disease and prevent cardiovascular events.
Irish CKD Guidelines 2 – Reduce overall cardiovascular risk: • Smoking cessation; • Weight loss; • Regular aerobic exercise; • Treat hypercholesterolemia (consider statin therapy); • Reduce thrombotic risk (consider aspirin therapy).
3. Other dietary factors which may be considered in early CKD Protein restriction: Dietary protein intake has been the focus of several trials. While there is evidence that protein restriction may delay the progression of CKD [8,9], it is not conclusive and must be weighted against the potential risk of malnutrition . Thus, a protein-controlled diet (0.80-1.0 g/kg IBW/day) is recommended 11.
Phosphorus Restriction: Dietary phosphorus control is central to the management of Chronic Kidney Disease Mineral and Bone Disorder (CKD - MBD) encompassing secondary hyperparathyroidism. Dietary phosphorus should be restricted once phosphate levels rise above normal 5,12,13 usually when eGFR level falls below 20 ml/min/1.73m2 5. While most guidelines agree that you should restrict phosphorus when serum phosphate levels are elevated, guidelines differ on how aggressively the whole area of hyperparathyroidism should be managed e.g. KDOQI advocate that patients should commence on a low phosphorus diet once PTH rises above normal 12, which occurs in the earlier stages of CKD 14, while the recent NICE guidelines suggest that calcium, phosphate and PTH should only be routinely monitored in stage 4 & 5 5. The reason for the difference in opinion is lack of clear evidence and cost benefit analysis; however research is currently underway to address these questions. Note: in most patient literature, the term phosphate is used both to describe phosphorus in food and phosphate in blood.Potassium Restriction: Dietary potassium should not be restricted routinely, only in those with raised serum levels, as potassium containing foods are required for a healthy balanced diet . On the other hand conservatively managed CRF patients should not be encouraged to have a free intake of high potassium foods such as fruits and vegetables. If serum potassium is >5.0mmol/L, potassium intake should be restricted . The use of ACE inhibitors angiotensin receptor blockers ARB used in the management of hypertension and proteinuria may contribute to hyperkalaemia and necessitate a potassium restriction. As kidney disease progresses the dietary management becomes more complicated and is reviewed in more detail elsewhere 11,15.
1. National Kidney Foundation: K/DOQI clinical practice guidelines for chronic kidney disease: evaluation, classification, and stratification. Am J Kidney Dis. 39: S1-266, 2002.
2. Irish CKD Guidelines. Irish Nephrology Society. 2007. Ref Type: Report.
3. Archibald G, Bartlett W, Brown A, Christie B, Elliott A, Griffith K, Pound S, Rappaport I, Robertson D, Semple Y, Slane P, Whitworth C, Williams B: UK Consensus Conference on Early Chronic Kidney Disease – 6 and 7 February 2007. Nephrol Dial.Transplant. 22:2455-2457, 2007.
4. Keith DS, Nichols GA, Gullion CM, Brown JB, Smith DH: Longitudinal follow-up and outcomes among a population with chronic kidney disease in a large managed care organization. Arch. Intern.Med. 164:659-663, 2004.
5. National Collaborating Centre for Chronic Conditions. Chronic kidney disease: national clinical guideline for early identification and management in adults in primary and secondary care. 2008. London, Royal College of Physicians. Ref Type: Report.
6. Drey N, Roderick P, Mullee M, Rogerson M: A population-based study of the incidence and outcomes of diagnosed chronic kidney disease. Am J Kidney Dis. 42:677-684, 2003.
7. Patel A, MacMahon S, Chalmers J, Neal B, Billot L, Woodward M, Marre M, Cooper M, Glasziou P, Grobbee D, Hamet P, Harrap S, Heller S, Liu L, Mancia G, Mogensen CE, Pan C, Poulter N, Rodgers A, Williams B, Bompoint S, de Galan BE, Joshi R, Travert F: Intensive blood glucose control and vascular outcomes in patients with type 2 diabetes. N.Engl.J Med. 358:2560-2572, 2008.
8. Levey AS, Greene T, Beck GJ, Caggiula AW, Kusek JW, Hunsicker LG, Klahr S: Dietary Protein Restriction and the Progression of Chronic Renal Disease: What Have All of the Results of the MDRD Study Shown? J Am Soc Nephrol 10:2426-2439, 1999.
9. Fouque D, Laville M, and Boissel JP. Low protein diets for chronic kidney disease in non diabetic adults. Cochrane Database of Systematic Reviews (2). 2006. Ref Type: Electronic Citation.
10. Locatelli F, Del Vecchio L: How long can dialysis be postponed by low protein diet and ACE inhibitors? Nephrol.Dial.Transplant. 14:1360-1364, 1999.
11. Renal Interest Group of Irish Nutrition & Dietetic Institute. Renal Nutrition Guidelines. 2006. Ref Type: Report.
12. National Kidney Foundation: K/DOQI Clinical Practice Guidelines for Bone Metabolism and Disease in Chronic Kidney Disease. Am.J.Kidney Dis. 42:S1-S202, 2003.
13. Levin A, Hemmelgarn B, Culleton B, Tobe S, McFarlane P, Ruzicka M, Burns K, Manns B, White C, Madore F, Moist L, Klarenbach S, Barrett B, Foley R, Jindal K, Senior P, Pannu N, Shurraw S, Akbari A, Cohn A, Reslerova M, Deved V, Mendelssohn D, Nesrallah G, Kappel J, Tonelli M, for the Canadian Society of Nephrology: Guidelines for the management of chronic kidney disease. CMAJ 179:1154-1162, 2008.
14. Levin A, Bakris GL, Molitch M, Smulders M, Tian J, Williams LA, Andress DL: Prevalence of abnormal serum vitamin D, PTH, calcium, and phosphorus in patients with chronic kidney disease: results of the study to evaluate early kidney disease. Kidney Int. 71:31-38, 2007.
15. Gilligan U: Diet and Renal Disease. Nutritionwise 1:14-16, 2007.