What laboratory tests should be ordered to evaluate preeclampsia?

Laboratory Evaluation for Preeclampsia

When evaluating suspected preeclampsia, order a minimum twice-weekly panel including: complete blood count (hemoglobin and platelet count), liver enzymes (AST, ALT, LDH), renal function tests (serum creatinine, electrolytes), and uric acid, along with urine protein assessment via dipstick followed by protein/creatinine ratio if positive (≥30 mg/mmol or 0.3 mg/mg is abnormal). 1

Core Laboratory Panel

The ISSHP 2018 guidelines provide the definitive framework for laboratory monitoring in preeclampsia 1:

Essential Blood Tests (Minimum Twice Weekly):

• Complete blood count: Hemoglobin and platelet count to detect thrombocytopenia and hemolysis
• Liver function: AST, ALT, and LDH to identify hepatocellular injury
• Renal function: Serum creatinine, electrolytes, and uric acid
• Additional liver assessment: International normalized ratio (INR), serum bilirubin, and serum albumin for comprehensive evaluation 1

Proteinuria Assessment:

• Initial screening: Automated dipstick urinalysis
• Quantification if positive: Spot urine protein/creatinine ratio (PCR) ≥30 mg/mmol (0.3 mg/mg) confirms significant proteinuria 1
• Note: 24-hour urine collection is no longer required routinely, though it remains indicated to confirm nephrotic syndrome (>5 g/24h), which has implications for thromboprophylaxis 1

Testing Frequency Based on Disease Severity

Recent evidence suggests risk-stratified laboratory monitoring intervals 2:

• Preeclampsia without severe features: Every 4 days
• Preeclampsia with severe features: Every 2 days
• Superimposed preeclampsia without severe features: Every 8 days
• Superimposed preeclampsia with severe features: Every 3 days

Critical caveat: Most laboratory abnormalities occur within 10 days of diagnosis, with earlier and more frequent abnormalities in those with severe features 2. Testing should be repeated immediately with any clinical status change.

Baseline Testing for Chronic Hypertension

Women with chronic hypertension require baseline laboratory evaluation to detect superimposed preeclampsia (which complicates up to 25% of these pregnancies) 1:

1. Full blood count
2. Liver enzymes and function tests
3. Serum creatinine, electrolytes, and uric acid
4. Urinalysis with microscopy and PCR
5. Renal ultrasound if serum creatinine or urine testing is abnormal

Important Clinical Nuances

Uric Acid Considerations:

While elevated gestation-corrected uric acid is not a diagnostic criterion for preeclampsia, it is associated with worse maternal and fetal outcomes and should prompt detailed fetal growth assessment 1. However, uric acid should not be used to determine timing of delivery 1.

Proteinuria Interpretation:

• Proteinuria is present in only ~75% of preeclampsia cases and is not required for diagnosis 1
• Negative dipstick can usually be accepted without further PCR testing at that time 1
• If proteinuria is diagnosed but subsequent dipsticks become negative, repeat quantification is appropriate 1
• Massive proteinuria (>5 g/24h) is associated with more severe neonatal outcomes 1

Emerging Biomarkers:

The ISSHP currently recommends against routine clinical use of PlGF or sFlt-1/PlGF ratio for rule-in or rule-out testing, as these should continue to be evaluated within clinical trials 1. However, NICE guidelines do endorse PlGF-based testing in specific circumstances 3, representing an area of guideline divergence.

Delivery Indications Based on Laboratory Findings

Women with preeclampsia should be delivered at ≥37 weeks or earlier if they develop 1:

• Progressive thrombocytopenia
• Progressively abnormal renal or liver enzyme tests
• Repeated severe hypertension despite triple therapy
• Pulmonary edema
• Abnormal neurological features
• Nonreassuring fetal status

Neither the degree of proteinuria nor the serum uric acid level should be used as indications for delivery 1.

Common Pitfalls to Avoid

1. Don't wait for proteinuria: Preeclampsia can be diagnosed without proteinuria if other maternal organ dysfunction is present
2. Don't rely on single readings: Average values over serial testing are more reliable than isolated abnormalities
3. Don't use outdated severity classifications: Avoid attempting to diagnose "mild versus severe" preeclampsia clinically, as all cases may become emergencies rapidly 1
4. Don't delay testing: Laboratory evaluation should be performed at least twice weekly and immediately with any clinical change 1