What is the test for proteinuria in pregnant women suspected of having preeclampsia?

Testing for Proteinuria in Preeclampsia

The spot urine protein-to-creatinine ratio (UPCR) is the recommended first-line quantitative test for proteinuria in suspected preeclampsia, with a diagnostic threshold of ≥30 mg/mmol (or ≥0.3 mg/mg). 1, 2

Recommended Testing Algorithm

Step 1: Initial Screening

• Perform automated dipstick urinalysis as the initial screening test at every antenatal visit after 20 weeks of gestation 1, 2
• A threshold of ≥1+ proteinuria (≥30 mg/dL) warrants proceeding to quantitative testing 1, 2
• Automated dipstick reading is superior to visual reading, with specificity of 93% versus 81% respectively 3

Step 2: Quantitative Confirmation

• If dipstick shows ≥1+, immediately obtain spot UPCR for quantification 1, 2
• UPCR ≥30 mg/mmol (or ≥0.3 mg/mg) confirms significant proteinuria when combined with new-onset hypertension after 20 weeks 1, 2
• UPCR demonstrates superior diagnostic accuracy (91.46%) compared to dipstick testing (59.76%) 4

Step 3: Alternative Testing Methods

• 24-hour urine collection (≥300 mg/24h) remains acceptable when UPCR is unavailable, though it is slower and prone to collection errors 2
• 24-hour collection is specifically indicated to confirm nephrotic-range proteinuria (>3 g/24h), which has implications for thromboprophylaxis 5, 6
• When neither UPCR nor 24-hour collection is available, dipstick values of ≥2+ (>1 g/L) provide reasonable assessment of true proteinuria 5

Critical Diagnostic Caveat

Proteinuria is NOT required for preeclampsia diagnosis. 1, 2 Preeclampsia can be diagnosed without proteinuria if new-onset hypertension after 20 weeks is accompanied by:

• Thrombocytopenia (platelets <100,000/μL) 2
• Elevated liver enzymes (transaminases >2× normal) 2
• Renal insufficiency (elevated serum creatinine) 2
• Pulmonary edema 2
• New-onset cerebral or visual symptoms 2
• Fetal growth restriction 2

Approximately 25% of women with genuine preeclampsia lack proteinuria but have life-threatening organ dysfunction 2

Performance Characteristics of Testing Methods

UPCR (Preferred Method)

• Sensitivity: 94.74% 4
• Specificity: 84.00% 4
• Positive predictive value: 93.10% 4
• Negative predictive value: 87.50% 4
• Results available within hours, eliminating collection errors 2

Dipstick Testing (Screening Only)

• Sensitivity: 68-81% 3, 7
• Specificity: 47-85% 3, 7
• Poor performance at excluding preeclampsia in hypertensive pregnant women 3
• May miss some proteinuric cases, though when missed, total protein excretion is usually <400 mg/day 5, 1

24-Hour Urine Collection

• Sensitivity: 80% 8
• Specificity: 100% 8
• Time-consuming and subject to collection errors 2

Clinical Significance of Proteinuria Levels

While proteinuria confirms diagnosis, delivery decisions should NOT be based on proteinuria degree alone 2:

• Massive proteinuria (>5 g/24h) is associated with more severe neonatal outcomes and earlier delivery 5, 1
• UPCR >900 mg/mmol (or >500 mg/mmol if age >35 years) correlates with worse maternal outcomes 5, 1
• However, the degree of proteinuria provides little additional risk stratification beyond confirming diagnosis (except in nephrotic syndrome) 5

Common Pitfalls to Avoid

• Do not rely on dipstick alone for diagnosis—always quantify with UPCR if ≥1+ 1, 2
• Do not delay diagnosis waiting for 24-hour collection—UPCR provides equivalent accuracy much faster 4
• Do not rule out preeclampsia based on negative proteinuria—check for other organ dysfunction 1, 2
• If proteinuria is initially diagnosed but subsequent dipsticks become negative, repeat quantification with UPCR to confirm whether true proteinuria persists 5, 1

Testing Not Currently Recommended

• Urinary albumin-to-creatinine ratio (UACR) has insufficient data to recommend its use at present 5, 1