Urinary Protein Excretion Estimation
Why Use
24-hour urine collection is time consuming, inconvenient for patients, and subject to collection error. The Urinary Protein Excretion Estimation avoids these problems without sacrificing accuracy, by using a single urine sample. Proteinuria is an independent risk factor for cardiovascular and renal disease, and predicts end organ damage. Detecting an increase in protein excretion has both diagnostic and prognostic value in initial detection and confirmation of renal disease. Quantifying proteinuria can also help assess effectiveness of therapy and progression of disease.
When to Use
Patients in whom renal disease is suspected (to rule out). Patients with known renal disease (to assess progression). Patients with low-grade proteinuria and otherwise intact renal function (to monitor).
Formula
Pearls / Pitfalls
The Urinary Protein Excretion Estimation (sometimes referred to as “spot urine protein/creatinine ratio” or “protein/creatinine ratio”) calculates the protein/creatinine ratio from a random urine sample to estimate 24-hour protein excretion. Based on the physiologic principle that urinary creatinine excretion is constant if glomerular filtration rate (GFR) is constant and therefore protein/creatinine ratio from a single urine sample should reflect protein excretion, cancelling out the time factor. Confirmed for correlation with 24-hour protein excretion in multiple studies (see Evidence Appraisal/EBM). Correlation is lowest for urine samples voided overnight and upon arising. Can be used only in presence of stable renal function (GFR). If albumin is the predominant component, persistent proteinuria suggests renal disease, even in the absence of decreased glomerular filtration rate, hypertension, or other abnormal findings on urinalysis.
Management
Patients with persistent low-grade proteinuria unrelated to decreased kidney function or a systemic disease typically have no long-term complications, even if untreated. Patients with low-grade proteinuria should be evaluated yearly to make sure it is not getting worse and that kidney function is stable. Many nephrologists use an antihypertensive drug, such as an angiotensin-converting enzyme (ACE) inhibitor or angiotensin II receptor antagonist (ARB), to reduce or eliminate proteinuria. Sodium-glucose cotransporter-2 (SGLT2) inhibitors are recommended for individuals with significant proteinuria, with or without diabetes. Renal biopsy may be warranted if (list is not exhaustive): UPEE is >3.5 g/day. Non-nephrotic range proteinuria with: Active urine sediment (e.g., cellular casts, hematuria). Reduced GFR. Progressing or persistent proteinuria. New-onset hypertension. For additional management recommendations, please refer to the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines .
Advice
UPEE >3.5 g/day in adults is associated with nephrotic syndrome. A decrease in protein excretion to <2 g/day, either in response to therapy or spontaneously, is associated with improved long-term prognosis. Additional workup for proteinuria should include a serum creatinine, glomerular filtration rate (GFR) estimation, and an examination for urine sediment (e.g., casts, acanthocytes).
More Information
Interpretation: UPEE <0.2 g/day Within normal limits UPEE 0.2–3.5 g/day Investigate further UPEE >3.5 g/day Nephrotic range