What level of proteinuria (protein in urine) is suspicious for preeclampsia (PET)?

Proteinuria Threshold for Suspecting Preeclampsia

Suspect preeclampsia when proteinuria reaches ≥300 mg in 24 hours, or more practically, when spot urine protein-to-creatinine ratio (PCr) is ≥30 mg/mmol (≥0.3 mg/mg), combined with new-onset hypertension after 20 weeks of gestation. 1

Initial Screening Approach

• Begin with automated dipstick urinalysis at every antenatal visit after 20 weeks of gestation 1, 2
• If dipstick shows ≥1+ proteinuria (≥30 mg/dL), proceed immediately to quantitative testing with spot urine PCr 1, 3
• A negative dipstick can usually be accepted without further testing at that time, though it may miss occasional cases where total protein excretion is typically <400 mg/day 1

Diagnostic Thresholds

Gold Standard (Traditional)

• 24-hour urine protein ≥300 mg is the time-honored diagnostic threshold 1, 2
• This value is more traditional than scientifically proven, but remains the accepted international standard 2

Preferred Practical Method

• Spot urine PCr ≥30 mg/mmol (or ≥0.3 mg/mg) is equivalent to 300 mg/24h and can replace 24-hour collection in most cases 1, 2, 3
• This eliminates the inherent difficulties of 24-hour collections and speeds up clinical decision-making 1
• The International Society for the Study of Hypertension in Pregnancy specifically recommends this 30 mg/mmol threshold for pregnant women at risk of preeclampsia 4

Critical Caveat: Proteinuria NOT Required for Diagnosis

Preeclampsia can be diagnosed WITHOUT proteinuria if new-onset hypertension after 20 weeks is accompanied by:

• Maternal organ dysfunction (thrombocytopenia, renal insufficiency, liver dysfunction, pulmonary edema, neurological symptoms) 2, 3
• Uteroplacental dysfunction 2

This is a common pitfall—do not rule out preeclampsia simply because proteinuria is absent. 2

Clinical Significance of Proteinuria Levels

While proteinuria confirms the diagnosis, its absolute quantification provides limited additional risk stratification with important exceptions:

• Massive proteinuria (>5 g/24h) is associated with more severe neonatal outcomes and earlier delivery 1, 2, 3
• Spot PCr >900 mg/mmol (or >500 mg/mmol if age >35 years) correlates with worse maternal outcomes 1, 2, 3
• Delivery decisions should NOT be based on proteinuria degree alone, but rather on maternal organ dysfunction, fetal status, and gestational age 2

Practical Testing Algorithm

1. Screen with dipstick at routine visits after 20 weeks 1, 2, 3
2. If ≥1+ (≥30 mg/dL), obtain spot urine PCr 1, 3
3. If PCr ≥30 mg/mmol (≥0.3 mg/mg) + new hypertension → diagnose preeclampsia 1, 2, 3
4. 24-hour collection is still indicated only to confirm nephrotic syndrome (>3.5 g/24h), which has implications for thromboprophylaxis 1

Common Pitfalls to Avoid

• Do not wait for proteinuria to diagnose preeclampsia—new hypertension with organ dysfunction is sufficient 2, 3
• Do not use dipstick alone for quantification—when neither 24-hour nor PCr measures are available, dipstick ≥2+ provides reasonable assessment, but quantification is preferred 1
• If proteinuria is initially diagnosed but subsequent dipsticks become negative, repeat quantification with PCr to confirm whether true proteinuria persists 1, 3
• PCr <30 mg/mmol occasionally gives false-negative results, but when this occurs, total protein excretion is usually <400 mg/day 1, 3