🩺 Proteinuria

Proteinuria is the presence of an abnormal amount of protein in the urine, indicating either glomerular basement membrane damage or tubular dysfunction. While small amounts can occur due to transient causes like exercise or fever, persistent proteinuria is a hallmark of chronic kidney disease (CKD). It is an independent risk factor for cardiovascular disease and renal progression. Classification depends on the amount (nephrotic vs sub-nephrotic) and the type of protein (albumin vs globulins/light chains). Management focuses on treating the underlying cause and reducing protein excretion through ACE inhibitors or ARBs.

Often asymptomatic but patients may report 'frothy' or 'foamy' urine, indicating high protein content. Enquire about systemic symptoms such as joint pain or rashes (suggestive of connective tissue disease), or weight loss and bone pain (suggesting myeloma). Screen for known triggers and comorbidities, particularly Diabetes Mellitus and Hypertension. Ask about a family history of renal disease (e.g., Alport syndrome) and recent medication changes, especially NSAIDs or gold salts.

Assess the patient’s fluid status carefully. Look for peripheral pitting oedema (ankles, sacrum), periorbital puffiness (more common in children), and signs of pleural effusion or ascites. Measure the blood pressure, as hypertension is a common feature of chronic kidney disease or glomerulonephritis. Inspect the skin for rashes (vasculitis or SLE) and the fundi for diabetic or hypertensive retinopathy, which may suggest the underlying cause of renal damage.

Diabetic Nephropathy; Minimal Change Disease (common in children); Focal Segmental Glomerulosclerosis (FSGS); Systemic Lupus Erythematosus (Lupus Nephritis); Multiple Myeloma (Light chains); Preeclampsia (in pregnancy).

Nephrotic range proteinuria (>3g/24h) with sudden onset oedema; Proteinuria in the context of pregnancy (highly suggestive of preeclampsia); Sudden decline in GFR associated with a rise in urine protein; Presence of haematuria and proteinuria (suggestive of acute glomerulonephritis).

Initial screening is via urine dipstick. Quantification is now performed using Protein:Creatinine Ratio (PCR) or Albumin:Creatinine Ratio (ACR) on a spot urine sample, rather than 24-hour collections. U&Es and eGFR are vital to assess renal function. Serum and urine electrophoresis (looking for paraproteins in Myeloma) and an immunology screen (ANA, ANCA, C3/C4) are often required. Gold standard for definitive diagnosis of glomerular disease is a renal biopsy. Ultrasound should be used to assess kidney size and structure.

Nephrotic-range proteinuria is defined as >3.5g/24h (or PCR >300mg/mmol), characterized by the triad of proteinuria, hypoalbuminaemia, and oedema. 'Orthostatic proteinuria' is a benign condition in adolescents where protein is only present in daytime samples; always test a first-morning void to exclude this. Bence-Jones protein (seen in Myeloma) is not detected on standard dipsticks, which only detect albumin.

Fits within the 'Renal' and 'Obstetrics' (preeclampsia) domains. Key focus on differentiating nephrotic vs nephritic syndromes and understanding the significance of ACR in diabetic monitoring.