Protein is normally too large to pass through the kidney's filtration membrane. When protein does appear in urine (proteinuria), it usually signals either a temporary, benign condition or — if persistent — something worth investigating more carefully.
Transient and benign causes
- Orthostatic proteinuria — common in adolescents and young adults; protein leaks when standing but not when lying down; benign and resolves with age
- Fever or vigorous exercise — can temporarily disrupt filtration; protein disappears when the cause resolves
- Dehydration — concentrated urine can appear to have elevated protein; check with hydration
Persistent proteinuria: when to investigate
Persistent proteinuria — found on two or more urine tests weeks apart — is clinically significant and requires further evaluation. The most common causes are diabetic nephropathy (kidney damage from diabetes) and hypertensive nephropathy (from longstanding high blood pressure). Other causes include glomerulonephritis, nephrotic syndrome, lupus nephritis and IgA nephropathy.
Quantification — via a spot urine albumin:creatinine ratio (ACR) or a 24-hour urine protein collection — tells your doctor how much protein is leaking and helps stage the severity.
How proteinuria is monitored and treated
Blood pressure control is the most important intervention for all forms of proteinuria — ACE inhibitors and ARBs have specific renoprotective effects beyond their blood pressure-lowering properties. In diabetes, tight glucose control is equally important. Regular ACR monitoring every 6–12 months in at-risk groups (diabetics, hypertensives) allows early detection before symptoms develop.