What tests and values indicate pre-eclampsia in a suspected patient?

Diagnostic Testing for Pre-eclampsia

When pre-eclampsia is suspected, immediately measure blood pressure and perform urine dipstick testing for proteinuria, followed by comprehensive laboratory evaluation including complete blood count, liver transaminases, serum creatinine, and quantification of proteinuria if dipstick is positive. 1

Essential Diagnostic Tests

Blood Pressure Measurement

• Measure blood pressure with properly calibrated equipment using appropriate cuff size (large cuff if mid-upper arm circumference >33 cm) 1
• Confirm systolic BP ≥140 mmHg and/or diastolic BP ≥90 mmHg on two separate occasions at least 15 minutes apart 1
• For severe hypertension (≥160/110 mmHg), confirmation is required within 15 minutes 1

Proteinuria Assessment

• Start with urine dipstick testing at every assessment after 20 weeks of gestation 2
• If dipstick shows ≥1+ (≥30 mg/dL), proceed immediately to quantification 3
• Quantification methods:
  • Spot urine protein-to-creatinine ratio (PCR) ≥30 mg/mmol (or ≥0.3 mg/mg) is the preferred rapid method 1, 3
  • 24-hour urine collection showing ≥300 mg protein is the traditional gold standard but time-consuming 2, 3

Comprehensive Laboratory Panel

Obtain at minimum twice weekly (more frequently if clinical deterioration): 1, 4

• Complete blood count with platelet count
• Liver transaminases (ALT/AST)
• Serum creatinine
• Uric acid (optional but helpful)

Diagnostic Values Indicating Pre-eclampsia

Core Diagnostic Criteria

Pre-eclampsia is diagnosed when new-onset hypertension (≥140/90 mmHg) after 20 weeks occurs with ANY ONE of the following: 1, 3

Proteinuria (if present):

• Spot urine PCR ≥30 mg/mmol (≥0.3 mg/mg) 1, 3
• 24-hour urine protein ≥300 mg 2, 3
• Dipstick ≥1+ (requires quantification for confirmation) 2, 3

Maternal Organ Dysfunction (even WITHOUT proteinuria):

• Thrombocytopenia: Platelet count <100,000/μL 1, 5
• Liver involvement: Transaminases >2× upper limit of normal 1, 5
• Renal insufficiency: Serum creatinine ≥1.1 mg/dL or doubling of baseline 1
• Neurological symptoms: Persistent severe headache unresponsive to medication or visual disturbances 1
• Pulmonary edema: Maternal pulse oximetry <90% 1

Uteroplacental Dysfunction:

• Fetal growth restriction on ultrasound 3
• Abnormal umbilical artery Doppler 6

Critical Diagnostic Pitfalls to Avoid

Proteinuria Is NOT Required

Approximately 25% of pre-eclampsia cases lack proteinuria 1, 3—never dismiss the diagnosis based on negative proteinuria if hypertension is present with other organ dysfunction 3. Women can develop life-threatening HELLP syndrome without any proteinuria 3, 4.

Symptoms Without Severe Hypertension

Do not dismiss symptoms in the absence of severe blood pressure elevation: 34% of eclamptic women had maximum diastolic BP ≤100 mmHg 2, 1. Headache is an independent risk factor for eclampsia, and epigastric pain predicts serious morbidity even without severe hypertension 2, 1.

Dipstick Limitations

A positive dipstick result alone is prone to false positives from reader error and concentration errors 2. Always quantify with PCR or 24-hour collection 2, 3. However, dipstick ≥1+ with new hypertension should be treated as pre-eclampsia until proven otherwise 2.

Fetal Compromise as First Sign

Fetal compromise (reduced fetal movements, small for gestational age) can be the first clinical indication of pre-eclampsia 2 and should always trigger immediate assessment of blood pressure and proteinuria 2.

Severity Assessment Values

Severe Features Requiring Immediate Action:

• Severe hypertension: BP ≥160/110 mmHg 1, 5
• Thrombocytopenia <100,000/μL 1, 5
• Liver transaminases >2× normal, especially with right upper quadrant or epigastric pain 1, 5
• Serum creatinine ≥1.1 mg/dL 1
• Persistent severe headache 1
• Visual disturbances (scotomata, cortical blindness) 1
• Pulmonary edema 1
• Eclampsia (seizures) 1

Practical Testing Algorithm

1. Immediate assessment when pre-eclampsia suspected:

   • Blood pressure measurement (confirm elevation) 1
   • Urine dipstick for proteinuria 2

2. If dipstick negative for proteinuria:

   • Obtain laboratory investigations to exclude pre-eclampsia: CBC, liver enzymes, creatinine 3
   • Evaluate fetal well-being with ultrasound 3

3. If dipstick ≥1+ or any concerning symptoms:

   • Quantify proteinuria with spot PCR (preferred) or 24-hour collection 2, 3
   • Complete laboratory panel: CBC with platelets, liver transaminases, creatinine 1, 4
   • Fetal assessment with ultrasound for growth and Doppler 4

4. Ongoing monitoring if pre-eclampsia confirmed:

   • Laboratory tests at least twice weekly (more frequently if deterioration) 1, 4
   • Blood pressure monitoring every 4 hours or more frequently if severe features 1