In 2000, chronic or unspecified renal failure was listed as a cause of death of 9160 Australians (7.1% of all deaths) (source: Australian Bureau of Statistics, special data request, 2002). Most would have had chronic renal impairment (CRI) for years. Each year, more than 1700 people with end-stage renal disease (ESRD) start dialysis or receive a transplant.1 These figures suggest that the impact of CRI is substantial and that in order to prevent progression to ESRD we need to develop systems for its detection and management.

Prevalence and significance of proteinuria. The Australian Diabetes, Obesity and Lifestyle (AusDiab) Study,2 a cross-sectional survey of a sample of over 11 000 Australians aged 25 and over, found proteinuria in 2.5% of the study population and a serum creatinine level above 120 µmol/L (reference range, 50–110 µmol/L [adult women], 60–120 µmol/L [adult men]) in 1.1%. A recent US study estimated that 1.5% of people aged six years and over have proteinuria.3 Extrapolating from these data, it is likely that several hundred thousand Australians have proteinuria, which is associated with a 15-fold increased risk of developing ESRD within 10 years.4

Whose urine should be screened? Current evidence does not support universal screening for proteinuria. The US Multiple Risk Factor Intervention Trial,5 in which more than 300 000 men were screened and followed up for an average of 16 years, showed that older age, smoking, hypertension and diabetes were significant risk factors for ESRD. Familial aggregation of ESRD, in excess of that predicted by clustering of diabetes and hypertension, has also been demonstrated.6 Indigenous Australians, who make up less than 2% of our population, comprise more than 8% of ESRD patients;1 and, in some remote communities where screening has been conducted, almost 25% of adults have been found to have proteinuria.7 Specific groups of people known to be at increased risk of ESRD should therefore be targeted for screening (see Box 1).

Dipstick testing is cheap (about $0.50 per test), with immediate results. More than a trace of protein indicates a protein excretion rate greater than 300 mg in 24 hours. In the AusDiab study,2 dipstick testing had about 85% sensitivity and specificity (S Chadban, Nephrologist, AusDiab Steering Committee, personal communication). As about 15% of people without proteinuria have a falsely positive result, people with a positive dipstick result should have their protein excretion rate quantified by further testing. Measurement of 24-hour urinary protein excretion rate has long been the gold standard, but reliable collection is often impractical. Measurement of the albumin–creatinine ratio (ACR) in a morning urine specimen is easier and sufficiently precise.9 An ACR over 34 g/mol indicates a daily protein excretion rate exceeding 300 mg. At the same time as measuring the urinary ACR, a blood sample should be sent for measurement of serum creatinine and electrolyte levels for further assessment of renal function.

Most dipsticks also test the urine for substances other than protein. If leukocytes or nitrites are detected, especially with symptoms suggestive of a urinary tract infection, a midstream urine specimen should be cultured. The dipstick test for proteinuria should be repeated after treatment of any infection. Isolated haematuria rarely indicates glomerular pathology associated with progressive renal disease. However, among smokers and people screened on the basis of age, a finding of haematuria should prompt exclusion of urinary tract malignancy.

Interpreting the serum creatinine level. Serum creatinine level per se is not an accurate indicator of renal function. The glomerular filtration rate (GFR), which can be estimated from the serum creatinine level, is the most meaningful single measure (see Box 2). In healthy adults, the GFR exceeds 80 mL/min; patients with a GFR between 30 and 80 mL/min have CRI; while a GFR below 30 mL/min indicates severe renal impairment with a high risk of progression to ESRD, warranting prompt referral to a nephrologist.

Managing CRI in general practice. General practitioners can substantially reduce the risk of progression of renal impairment. Management guidelines developed by the Australian Kidney Foundation and the Australia and New Zealand Society of Nephrology are accessible at the "Caring for Australians with Renal Impairment" website.11 I discuss here the evidence for the interventions recommended in the guidelines. Further benefit may be obtained by reducing the high risk of cardiovascular events that accompanies renal disease.12

Intensive control of hyperglycaemia and hypertension is beneficial for people with diabetes. (Specific interventions for diabetes are beyond the scope of this article — see the guidelines of the Australian Diabetes Society.8)

In all patients with CRI, management aims should be the reduction of proteinuria (to ACR < 100 g/mol) and the maintenance of renal function (ie, stable GFR). These can be achieved through intensive control of hypertension11 (Level I evidence13). Suggested blood-pressure targets are 125/75 mmHg (in people under 50 years) and 135/85 mmHg (in people ≥ 50 years). Multidrug therapy is usually required. Angiotensin-converting enzyme inhibitors and angiotensin-II-receptor antagonists have been shown to be renoprotective (Level I and Level II evidence, respectively).11 Even in the absence of hypertension, they may be effective in people with protein excretion exceeding 1 g/day (ie, an ACR above 100 g/mol). Treatment for this normotensive group should be adjusted according to the level of proteinuria and monitored with three- to six-monthly ACR estimates. Potential risks include hyperkalaemia and, in patients with renal artery stenosis, worsening of renal impairment. In randomised controlled trials of these agents, participant dropout rates due to adverse effects have been low.

Because smoking is associated with increased risk of progression of renal impairment (Level III-2 evidence),11 smokers should be assisted to quit smoking. A low-protein diet is not recommended, as the benefit is minimal and malnutrition may ensue. There is little evidence regarding the impact of exercise; however, in view of its cardiorespiratory benefits, regular exercise is advised. There is currently insufficient evidence to warrant lipid-lowering therapy as a means of minimising progression.

Who should be referred to a nephrologist? GPs can usually manage patients with CRI, preventing further renal damage and progression to renal failure. Indications for prompt referral to a nephrologist include

• estimated GFR below 30 mL/min;

• estimated GFR above 30 mL/min, but declining rapidly;

• age less than 35;

• ACR greater than 300 g/mol (nephrotic range for proteinuria);

• symptoms or signs suggestive of systemic illness (eg, systemic lupus erythematosus); or

• failure to reach blood pressure or ACR targets within six months of starting antihypertensive drug therapy.