What test is used to check for protein in the urine?

Testing for Proteinuria

Order a spot urine protein-to-creatinine ratio (UPCR) or urine albumin-to-creatinine ratio (UACR) as your first-line quantitative test to check for protein in the urine. 1, 2

Initial Screening Approach

• Begin with automated dipstick urinalysis when available for initial screening, using a first morning void sample when possible (though random specimens are acceptable). 3, 4
• If the dipstick shows ≥1+ protein (≥30 mg/dL), you must confirm with quantitative testing—never rely on dipstick alone for diagnosis. 2, 3, 4

Preferred Quantitative Tests (in Order of Preference)

The KDIGO 2012 guidelines recommend the following hierarchy for proteinuria testing: 1

1. Urine albumin-to-creatinine ratio (UACR) - Most preferred
2. Urine protein-to-creatinine ratio (UPCR) - Second choice
3. Reagent strip urinalysis with automated reading - Third choice

Why Spot Ratios Are Preferred

• UPCR and UACR are more convenient, faster, and eliminate collection errors compared to 24-hour urine collections. 2
• Use first morning void to minimize variability, though random specimens are acceptable for most clinical scenarios. 1, 2
• Normal UPCR is <200 mg/g (<0.2 mg/mg); abnormal is ≥200 mg/g. 2
• For UACR, normal is <30 mg/g; abnormal is ≥30 mg/g. 2, 3

When to Use 24-Hour Urine Collection

Reserve 24-hour collections for specific situations only: 2

• Confirming nephrotic syndrome (>3.5 g/day) when thromboprophylaxis decisions are needed
• Patients with glomerular disease requiring initiation or intensification of immunosuppression
• Extremes of body habitus (cachexia, muscle atrophy, extreme obesity) where creatinine excretion is abnormal
• When there are discrepancies between spot ratio results and clinical presentation

Confirmation Requirements

• Confirm any elevated result with repeat testing—transient proteinuria is common. 2, 3
• Persistent proteinuria requires 2 of 3 positive samples over 3 months in non-pregnant patients. 2, 3
• Before confirming, exclude benign causes: urinary tract infection, vigorous exercise within 24 hours, menstrual contamination, fever, or marked hyperglycemia/hypertension. 2, 4

Special Population Considerations

Diabetic Patients

• Use UACR specifically (not total protein) for screening and monitoring diabetic kidney disease. 3
• UACR is more clinically meaningful than total proteinuria in diabetes. 3

Pregnant Patients

• Use a threshold of ≥300 mg/g (0.3 mg/mg) for UPCR to indicate abnormal proteinuria in pregnancy (higher than the general population threshold). 2

Common Pitfalls to Avoid

• Never diagnose proteinuria based on dipstick alone—dipstick has 31.6% false-negative rate and misses pathological proteinuria frequently. 5, 6
• Don't order 24-hour collections routinely when spot ratios are adequate for clinical decision-making. 2
• Avoid testing during transient conditions (UTI, exercise, fever) that cause false elevations. 2, 4
• Don't measure spot urine albumin or protein concentration alone without simultaneous creatinine—this is susceptible to false results due to hydration variations. 3

Reporting Standards

• Laboratories should report UACR and UPCR as ratios (not concentrations alone) in units of mg/g. 1, 2
• The term "microalbuminuria" should no longer be used. 1