Diagnosis and management of nephrotic syndrome.

Nephrotic syndrome is defined by a triad of clinical features: oedema, substantial proteinuria (> 3.5 g/24 hours) and hypoalbuminaemia (< 30 g/L). It is often associated with hyperlipidaemia, thromboembolism and an increased risk of infection. Nephrotic syndrome develops following pathological injury to renal glomeruli. This may be a primary problem, with a disease specific to the kidneys, or secondary to a systemic disorder such as diabetes mellitus. The most common cause in children is minimal change glomerulonephritis. In white adults, nephrotic syndrome is most frequently due to membranous nephropathy whereas in populations of African ancestry the most common cause of nephrotic syndrome is focal segmental glomerulosclerosis. Diabetic nephropathy is the most common multisystem disease that can cause nephrotic syndrome. Patients typically present with periorbital oedema (most noticeable in the morning) or dependent pitting oedema (more common later in the day). Proteinuria should be documented by a quantitative measurement e.g. urine protein: creatinine ratio (PCR) or albumin: creatinine ratio (ACR). PCR > 300-350 mg/mmol indicates nephrotic range proteinuria. Urgent referral to a nephrologist (ideally within 2 weeks) is necessary and a renal biopsy is usually performed. This will establish what form of glomerular disease is responsible. Additional tests may be undertaken to assess if nephrotic syndrome is secondary to another disorder e.g. systemic lupus erythematosus or amyloidosis.