From the Guidelines
Protein in urine, known as proteinuria, requires immediate medical evaluation as it may indicate kidney problems, and the most recent guideline recommends using untimed urine samples to detect and monitor proteinuria 1.
Key Points to Consider
- Proteinuria occurs when the kidneys' filtering system becomes damaged, allowing proteins (particularly albumin) that should remain in the bloodstream to leak into the urine.
- Common causes include diabetes, high blood pressure, glomerulonephritis, certain medications, urinary tract infections, and pregnancy-related conditions.
- The severity and persistence of proteinuria help determine its significance - transient proteinuria can occur with fever or exercise, while persistent proteinuria often indicates underlying kidney disease requiring treatment.
- According to the guideline, the ratio of protein or albumin to creatinine in an untimed urine specimen has replaced protein excretion in a 24-hour collection as the preferred method for measuring proteinuria 1.
- A study published in 2012 recommends long-term ACEi or angiotensin receptor blockers (ARB) treatment when proteinuria is ≥1 g/day, with uptitration of the drug depending on BP 1.
Recommendations for Patients with Proteinuria
- If you notice protein in your urine through testing, you should consult your healthcare provider for proper assessment.
- No specific medication can be recommended without determining the underlying cause.
- Your doctor will likely order additional tests including a comprehensive urinalysis, blood tests to check kidney function, and possibly imaging studies or a kidney biopsy in some cases.
- While waiting for your appointment, maintain good hydration, follow a balanced diet lower in salt, and continue taking any prescribed medications for conditions like diabetes or hypertension.
- Reduction of proteinuria to ≤1 g/day is associated with a more favorable prognosis irrespective of whether the initial proteinuria was ≥3 g or of lesser degrees 1.
From the Research
Proteinuria Diagnosis and Measurement
- Proteinuria is a key indicator of renal disease and can be measured through 24-hour urinary total protein excretion rate or spot urine protein creatinine ratio 2, 3, 4.
- The 24-hour urinary total protein excretion rate is considered the gold standard for measuring proteinuria, but it can be time-consuming, cumbersome, and prone to collection errors 2, 3, 4.
Spot Urine Protein Creatinine Ratio as an Alternative
- The spot urine protein creatinine ratio has been shown to be a reliable alternative to the 24-hour urinary total protein excretion rate in non-diabetic chronic renal disease patients 2.
- Studies have demonstrated a significant correlation between spot urine protein creatinine ratio and 24-hour urinary total protein excretion rate in patients with various levels of proteinuria and physical activity 3, 4, 5.
- However, the accuracy of the spot urine protein creatinine ratio may be affected by factors such as physical activity and the level of proteinuria 3, 6.
Disease-Specific Considerations
- In patients with immunoglobulin A nephropathy, the spot urine protein creatinine ratio has been shown to be a reliable estimate of 24-hour proteinuria 6.
- In contrast, the spot urine protein creatinine ratio may not be a reliable estimate of 24-hour proteinuria in patients with membranous nephropathy or minimal change disease 6.
- In patients with lupus nephritis, the urinary protein creatinine ratio has been shown to be a useful tool for evaluating proteinuria, but its accuracy may vary depending on the level of proteinuria and physical activity 5.