Proteinuria: Causes, Symptoms & Treatment
Proteinuria refers to elevated levels of protein in the urine. It can be a sign of kidney disease or other underlying medical conditions.
Things worth knowing about "Proteinuria"
Proteinuria refers to elevated levels of protein in the urine. It can be a sign of kidney disease or other underlying medical conditions.
What is Proteinuria?
Proteinuria is the presence of abnormally high amounts of protein in the urine. Healthy kidneys filter the blood while retaining large molecules such as proteins, allowing only very small amounts to pass into the urine. When more than 150 mg of protein per day is excreted in the urine, the condition is referred to as proteinuria. It is not a disease in itself, but a clinical finding that may indicate kidney damage or other systemic conditions.
Causes
Proteinuria can result from a wide range of causes. A key distinction is made between temporary (transient) and persistent forms:
Transient Causes
- Intense physical exercise
- Fever or acute infections
- Dehydration
- Emotional stress
- Orthostatic proteinuria (occurring when standing, not when lying down)
Persistent Causes
- Diabetic nephropathy: kidney damage caused by diabetes mellitus
- Glomerulonephritis: inflammation of the glomeruli (filtering units of the kidney)
- Nephrotic syndrome: significant protein loss through the kidneys
- High blood pressure (arterial hypertension)
- Lupus erythematosus and other autoimmune diseases
- Infections such as HIV or hepatitis B and C
- Certain medications and nephrotoxic substances
- Amyloidosis (protein deposits in tissue)
Symptoms
Mild to moderate proteinuria usually causes no noticeable symptoms and is often discovered incidentally during a routine check-up. In cases of severe proteinuria, the following signs may appear:
- Foamy urine: caused by the surface tension of proteins in the urine
- Edema (swelling): fluid accumulation in the legs, ankles, or face due to low protein levels in the blood
- Fatigue and general malaise
- Weight gain due to fluid retention
Additional symptoms specific to the underlying condition may also be present.
Diagnosis
The diagnosis of proteinuria is established through several tests:
- Urine dipstick test: a simple screening method; a positive result requires confirmation
- 24-hour urine collection: precise measurement of total daily protein excretion
- Albumin-to-creatinine ratio (ACR) in a spot urine sample: a quick and reliable method for quantification
- Blood tests: kidney function markers (creatinine, urea), albumin, electrolytes
- Kidney biopsy: performed when the cause is unclear, for detailed tissue analysis
- Imaging studies such as renal ultrasound
Degrees of Proteinuria
- Microalbuminuria: 30–300 mg of albumin per day (early sign of kidney involvement)
- Macroalbuminuria: more than 300 mg of albumin per day
- Nephrotic-range proteinuria: more than 3.5 g of protein per day
Treatment
Treatment of proteinuria is directed at the underlying cause. The main goals are to reduce protein excretion, protect kidney function, and prevent complications.
Medical Treatment
- ACE inhibitors or angiotensin receptor blockers (ARBs): reduce pressure within kidney vessels and lower proteinuria; first-line therapy for diabetic nephropathy and hypertension
- SGLT2 inhibitors: newer medications with nephroprotective effects
- Immunosuppressants: used for inflammatory kidney diseases such as glomerulonephritis
- Diuretics: help reduce edema by promoting fluid excretion
General Measures
- Optimal blood pressure control (target below 130/80 mmHg)
- Blood sugar management in diabetes mellitus
- Low-protein diet in advanced kidney insufficiency (as advised by a physician)
- Low-sodium diet
- Avoiding nephrotoxic substances (e.g., certain pain relievers such as NSAIDs)
- Regular monitoring of kidney function
Prognosis
The prognosis depends strongly on the underlying condition and the severity of protein excretion. Early treatment can significantly slow or halt the progression of kidney disease. If left untreated, persistent proteinuria can lead to chronic kidney failure.
References
- Kidney Disease: Improving Global Outcomes (KDIGO) - KDIGO 2024 CKD Guideline. Kidney International, 2024.
- Kasper, D. L. et al. - Harrison's Principles of Internal Medicine, 21st Edition, McGraw-Hill, 2022.
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) - Proteinuria (Protein in Urine). U.S. Department of Health and Human Services, 2023.
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