Focus on chronic kidney disease
Dr Andrew Palmer MB BS FRCP is a consultant nephrologist at Bupa Cromwell Hospital and Hammersmith Hospital and Harefield Hospital.
The National Kidney Foundation (NKF) defines chronic kidney disease (CKD) as either kidney damage or a decreased glomerular filtration rate (GFR) of less than 60 mL/min/1.73 m2 for three or more months. It represents the destruction of renal mass, irrespective of the underlying etiology, leading to a progressive decline in GFR with irreversible damage and loss of nephron mass.
The last 10 - 15 years has seen a remarkable increase in the recognition of chronic renal disease. Prior to this, the management of patients on dialysis and transplantation dominated the care of patients with renal disease. However, with an estimated more than 1.1 million patients worldwide requiring maintenance dialysis and a seven percent increase each year, it has switched attention to the early intervention and prevention of end-stage renal failure.
Silent symptoms affect incidence rates
The true extent of renal disease is not known. The incidence is determined by a number of factors including age, ethnicity and social class. In 2001, a study of laboratory results in the South East of England (a predominantly Caucasian population) found a prevalence of CKD (Stages 3-5) of 5,554 per million population (pmp), with 85 percent unknown to renal services. The fact that symptoms are often silent in patients with chronic kidney disease represents one of the major challenges in determining the extent of the problem.
We know that patients with lesser degrees of renal impairment, and in particular Stage 3 CKD, are common particularly in an aging population. There is a natural decline in renal function so that the majority of patients over 70 will not have a normal GFR and patients over 80 often have GFRs down to 50 mls/min.
The importance of ethnicity also cannot be underestimated. Indo-Asian or Afro-Caribbean patients over 60 are 10 times more likely to develop end-stage renal failure than their Caucasian counterparts.
Classification of chronic kidney disease
The management of chronic kidney disease was transformed in 2002 with the K/DOQI classification of the stages of chronic kidney disease into five stages based on eGFR (see below).
This classification provided the impetus for more modest degrees of renal impairment to be recognised as the pathway to ESRF (see to diagram to right) and that end-stage renal failure is the ‘tip of the iceberg’ so to speak.
Major causes of chronic kidney disease
There are many causes of chronic kidney disease, but for day-to-day clinical practice it is important to remember that the majority of renal disease is covered by relatively few conditions (see below).
Making an accurate diagnosis
The diagnosis of CKD is often incidental, either occurring during routine blood tests, investigation of other medical conditions or in well-patient clinics or insurance medicals.
The mainstay of diagnosis remains laboratory investigation of renal function and measuring serum creatinine levels. However, this often does not give an accurate representation of kidney function as there may already be a 50 percent reduction in renal function by the time the creatinine is elevated. This has led to the use of the estimated GFR (eGFR) – a formula-based calculation of glomerular filtration rate – as a method of assessing renal function and gauging the need for further investigation or referral.
The principal drawback to the use of MDRD eGFR is that it does not take body mass into account and therefore patients who are of a very small or large build can have misleading results. A 130 kg body builder could have an elevated a serum of creatinine of 140 umol/l with an eGFR of < 60 mls / min suggesting CKD3, but his true renal function is normal with a GFR of 120 mls / min when taking into account his weight. In contrast, patients of a small build may have more advanced CKD than suggested by their eGFR results. The use of the Cockroft-Gault calculation (easily accessible on the Internet) is often helpful in this situation.
Early diagnosis and treatment of the underlying cause and/or institution of secondary preventive measures is essential in the management of chronic kidney disease.
Diagnosis of the cause means that specific treatment can be instituted, such as the relief of obstruction, giving immunosuppressive therapy where appropriate for glomerular disease, and renal angioplasty and stenting in renovascular disease. This must not be overlooked as such measures can halt, or sometimes reverse, the decline in renal function and avoid future renal replacement therapy.
For most types of renal disease certain measures can significantly attenuate the progression of chronic kidney disease. Improved blood pressure, lipids and in diabetes, glycaemic control, are essential in preserving renal function. There are now many trials demonstrating the value of angiotensin converting enzyme inhibitors and A2 receptor blockers, sometimes together, in slowing the decline of renal function in patients with CKD. It is also important that patients are followed up and advised to avoid renal insults such as the use of NSAIDs.
Early prevention of complications is equally important, which often happen with less compromised renal function than previously recognised. These include lipid-lowering, blood pressure control and stopping smoking to reduce the impact of the huge cardiovascular risk in later life, and which accounts for the major morbidity and mortality in ESRF.
Development of renal bone disease often starts earlier than realised in patients with Stage 3 CKD and most patients will require consideration of Erythropoitein as their renal function declines. The management of acidosis is now of increasing importance not only in terms of potassium control, but also in terms of preserving renal function.
When to refer patients
The size of the population of patients diagnosed with CKD means that only a relatively small proportion will come under the care of a nephrologist, especially in the elderly where CKD is so prevalent. It is therefore important that CKD patients cared for in the community are recognised and monitored, which is usually the case. It is essential to ensure patients maintain stable function and do not contribute to the ever-expanding renal replacement therapy programme in the UK.
Only a modest proportion of patients will lose function but it is essential such patients are investigated, referred as necessary, and more closely followed up. The majority of these patients are Stage 3 and remain the greatest challenge to ensure a balance is kept between providing unnecessary hospital care and avoiding late referral which can lead to increased morbidity, longer hospital stays, and a higher cost of treatment when starting long-term dialysis. It likely that most Stage 4 and Stage 5 cases will need some form of hospital-based care.