The basics - Chronic kidney disease

CKD can be a challenging but rewarding condition to manage in general practice, writes Dr Keith Barnard.

Chronic kidney disease (CKD) is a major cause of morbidity and mortality and is common in the UK, with an estimated incidence of 1,700 per million of the population.1

If a patient with CKD is likely to need dialysis, a psychoeducational programme should be offered (SPL)

According to the widely adopted classification system, CKD can be divided into five stages, as shown in the box (right).

Prevalence figures of patients with stage 3-5 CKD show a rapid increase with age, as shown in the box below. Only 4 per cent of CKD patients are accepted for renal replacement therapy.

Patients do not inevitably progress through the stages. In fact most patients remain stable. CKD is more prevalent in deprived areas, and cardiovascular disease (CVD) is the most common cause of death in CKD patients.

Stages of CKD

Stage 1: GFR >90ml/min (if with another abnormality,* otherwise
regard as normal)
Stage 2: GFR 60-89ml/min (if with another abnormality,* otherwise regard
as normal)
Stage 3A: GFR 45-59ml/min (moderate impairment)
Stage 3B: GFR 30-44ml/min (moderate impairment)
Stage 4: GFR 15-29ml/min (severe impairment)
Stage 5: GFR <15ml/min (established renal failure)

* such as existing proteinuria, haematuria, microalbuminuria in
diabetes, polycystic disease or reflux nephropathy


Source: The Renal Association.

CKD is more common within South Asian, African and African-Caribbean communities. Median survival is about three years, but this varies greatly in relation to the stage of renal failure at diagnosis and the age of the patient.

One of the main difficulties for GPs is that cases may go unrecognised for many years, because there are no specific presenting symptoms. Often the diagnosis is not made until late in the progression of the disease, when it carries a much higher risk of mortality.

CKD often co-exists with other significant pathologies, such as CVD and diabetes mellitus. The presence of unrecognised disease is of great importance, because there is good evidence that treatment can prevent or delay the progression of CKD.

Early identification of CKD
About 30 per cent of patients with advanced kidney disease are referred late to specialised nephrology services from primary and secondary care. This is a clear indication that strategies are required to allow earlier identification of CKD so that progression to renal failure can be avoided wherever possible.

NICE suggests in its 2008 guideline on early identification and management of CKD2 that tests for the condition should be performed in all patients with diabetes, hypertension, CVD or cerebrovascular disease, and in those with structural renal tract disease, renal calculi or prostatic hypertrophy.

Patients with multisystem diseases with potential kidney involvement such as systemic lupus erythematosus, and those with a family history of stage 5 CKD or hereditary kidney disease should also be screened.

Cases where haematuria or proteinuria are found on opportunistic testing should also be investigated for CKD.

NICE also suggests that stage 3 CKD should be divided into two subcategories, with stage 3A being those with an eGFR of 45-59ml/min and stage 3B those with an eGFR of 30-44ml/min.

Proteinuria has both diagnostic and predictive value in the detection and confirmation of renal disease, but urine dipstick testing alone is not a reliable indicator.

NICE recommends measuring the urine albumin:creatinine ratio (ACR) in preference to the protein:creatinine ratio (PCR), because it has greater sensitivity. For diabetics, only the ACR should be used.

Measuring GFR
Measuring the glomerular filtration rate (GFR) is the best way to accurately assess renal function. Because this is normally about 100ml/min, it approximately represents the percentage of normal kidney function.

Serum creatinine alone does not detect minor degrees of renal impairment and is not directly related to the GFR, but because measuring the GFR is a time-consuming process, it is now usually estimated by the laboratory, and is referred to as the estimated glomerular filtration rate (eGFR).

It is calculated from a formula using the serum creatinine, gender and age. A correction factor of 1.2 should be applied for patients of African-Caribbean origin. It is important to monitor progression of CKD by measuring three eGFR values over a period of 90 days or more. Progression is defined as decline in eGFR of >5ml/min within one year.

Prevalence rates of CKD, stages 3-5
Age group18-2425-3435-4445-5455-6465-7475-8485+
Male0.01% 0.17%0.71%3.08%6.89%17.65%33.16%44.75%
Female0.18%0.79%2.69%2.79%13.09%27.86%41.68%48.61%

Management of CKD
In all stages of CKD, regular clinical and laboratory assessment should be carried out, and all patients should be given advice on smoking, weight, exercise and salt and alcohol intake.

Cardiovascular prophylaxis with aspirin and/or lipid lowering drugs should be considered if the patient has a >20 per cent risk at 10 years. BP should be carefully controlled, with a target value of 130/80mmHg.

If the urine PCR value is >100mg/mmol and the patient has diabetes or microalbuminuria, ACE inhibitors or angiotensin receptor blockers (ARBs) should be used.

It is important to check creatinine and potassium levels before starting treatment and to check them again two weeks after starting and after any changes of dosage. If the creatinine increases by >20 per cent or the eGFR falls by >15 per cent, specialist advice should be sought.

It may be necessary to stop treatment and check for renal artery stenosis.

If the potassium rises to >6mmol/l and there has been no haemolysis of the sample, any drugs that could alter potassium levels should be stopped. If patients cannot tolerate ACE inhibitors or ARBs, non-dihydropyridine calcium-channel blockers should be considered.

Dietary protein restriction is not necessary in the early stages of CKD but, in all patients with hypertension, a reduction in sodium to less than 2.4g/day is recommended. Salt substitutes with high amounts of potassium salts should not be used.

In patients with CKD of stage 3 or more, nutritional status should be monitored to avoid malnutrition. Specialist psychological advice should be available, and if a patient is likely to need dialysis, a psychoeducational programme should be offered.

Anaemia is often a problem in CKD, and erythropoiesis-stimulating agents can markedly improve quality of life. For patients in stage 3, 4 and 5 CKD, additional management should include renal ultrasound, the avoidance of nephrotoxic drugs and immunisation against influenza and pneumococcus.

When to refer
Urgent referral is required if there is malignant hypertension, hyperkalaemia >7mmol/l or nephrotic syndrome.

In stages 1-2, referral should be considered if there is isolated proteinuria (PCR >100mg/mmol), proteinuria (PCR>45mg/mmol) with microscopic haematuria, diabetes with proteinuria (PCR>100mg/mmol) but no retinopathy, macroscopic haematuria, pulmonary oedema with normal left ventricular function, or if the eGFR falls more than 15 per cent in the two months after starting ACE or ARB therapy.

Time and effort spent detecting and managing CKD is rewarded by the fact that, with optimum treatment, patients can have the progression to end stage renal disease halted or delayed by many years.

  • Dr Barnard is a former GP in Hampshire.

References

1. 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 2003; 42(4): 677-84.

2. NICE Clinical guideline 73. Early identification and management of chronic kidney disease in adults in primary and secondary care. London: NICE, 2003. http://www.nice.org.uk/guidance/CG73

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