proteinuria

Proteinuria is the presence of excess protein in the urine. In adults, normal urinary protein excretion is typically less than about 150 mg per day; clinically significant proteinuria is often defined as more than 150 mg/day or a positive dipstick result for protein. Proteinuria can be transient and benign or persistent and a sign of kidney disease.

Causes include transient or functional proteinuria, which can occur with fever, exercise, dehydration, or orthostatic changes and usually resolves with rest or rehydration. Persistent proteinuria may reflect kidney disease and is categorized by mechanism: glomerular proteinuria due to increased glomerular permeability (often albumin); tubular proteinuria due to reduced proximal tubular reabsorption of filtered proteins; overflow proteinuria due to excess production of filtered proteins such as light chains or myoglobin.

Evaluation typically begins with a urine dipstick test. For quantification, providers use the urine protein-to-creatinine ratio (UPCR) or the albumin-to-creatinine ratio (ACR) from a spot urine sample, or a 24-hour urine collection for precise measurement. Distinguishing albuminuric from non-albumin proteinuria is important; electrophoresis or specific assays may help identify particular proteins in selected cases.

Clinical significance centers on proteinuria as a marker of kidney disease and as a prognostic factor. Nephrotic-range proteinuria (>3.5 g/day) with hypoalbuminemia, edema, and hyperlipidemia defines nephrotic syndrome. Microproteinuria (often in the range of 30–300 mg/day or mg/g) is a risk marker in diabetes and hypertension. Persistent proteinuria indicates a higher risk of progression to chronic kidney disease.

Management focuses on identifying and treating the underlying cause. In many patients with hypertension or diabetes, renin-angiotensin-aldosterone system blockade (ACE inhibitors or ARBs) reduces proteinuria and protects kidney function. Additional measures include optimizing blood pressure and glycemic control, lipid management, and lifestyle modification. In pregnancy, new-onset proteinuria requires obstetric evaluation for preeclampsia.