Proteinuria: Causes, Symptoms, and Treatment
Proteinuria is the presence of protein in the urine, meaning the body is excreting more protein than normal. This condition can occur temporarily or be a sign of an underlying health issue.
Functional proteinuria may happen during stress, physical exertion, dehydration, or fever. In such cases, daily protein excretion typically does not exceed 150–250 mg.
Pathological proteinuria, however, refers to daily protein loss exceeding 300–500 mg and often indicates a serious kidney or systemic problem.
What Causes This Condition?
The most common cause is glomerulonephritis, which damages the filtration barrier in the kidneys and allows proteins like IgG, IgM, and albumin to pass into the urine. When albumin predominates, this is known as microalbuminuria, diagnosed when excretion exceeds 30 mg per 24 hours.
Another type is tubular proteinuria, which occurs when the kidney’s filtering barrier is intact, but the tubules cannot reabsorb smaller proteins efficiently. This usually happens in tubulointerstitial nephropathies. Generally, protein levels are higher in glomerular proteinuria than in tubular forms.
Moreover, this condition can be linked to chronic kidney disease and systemic diseases such as diabetes, lupus, Fabry disease, Fanconi syndrome, and sickle cell anemia. In some blood disorders like multiple myeloma or Waldenström’s macroglobulinemia, abnormal proteins such as Bence-Jones protein appear in the urine.
Signs and Symptoms of Proteinuria
Under normal circumstances, the kidneys excrete about 80 ± 24 mg of protein per day. Nephrotic syndrome occurs when proteinuria exceeds 3.5 g/24h and is often accompanied by:
- Hypertension
- Swelling (around the eyes, ankles, sacral area, or genitals)
- Blood in urine
- Reduced kidney function (GFR)
- High cholesterol and lipid levels
- Foamy urine
If left untreated, persistent protein loss may lead to high blood pressure, anemia, and imbalances in calcium and phosphorus metabolism.
How Is It Diagnosed?
Diagnosis involves a combination of urine, blood, and imaging tests. Typical assessments include:
- Urinalysis and sediment examination
- Ultrasound
- Biochemical tests, including GFR, creatinine, total protein, albumin, calcium, phosphate, ESR, and lipid profile
If protein excretion exceeds 1 g/24h, urgent medical evaluation is necessary, as this condition is also an independent cardiovascular risk factor.
Treatment Options
Treatment focuses on addressing the underlying cause and controlling complications. For instance:
- Blocking the RAAS system with ACE inhibitors or angiotensin receptor blockers may slow kidney damage and reduce protein loss.
- Managing blood pressure and correcting water-electrolyte imbalances
- Treating systemic diseases contributing to proteinuria
With timely treatment, this condition can be controlled or improved, lowering the risk of long-term kidney and cardiovascular complications.
Key Takeaway: Proteinuria is more than just a symptom: it is a signal that the kidneys or systemic health may be at risk. However, with early detection and proper treatment, its complications can often be prevented.
References
Frontiers in Medicine. “Monogenic Causes of Proteinuria in Children.” Frontiers in Medicine, 2018.
PMC (National Center for Biotechnology Information). “Rare Inherited Kidney Diseases: An Evolving Field in Nephrology.” PMC, 2020.
SpringerLink. “Tubular Proteinuria Due to Hereditary Endocytic Receptor Defects.” Pediatric Nephrology, 2025.