What laboratory tests are recommended for a pregnant woman suspected of having preeclampsia and what is the rationale for each test?

Laboratory Tests for Preeclampsia

When preeclampsia is suspected, obtain a comprehensive laboratory panel including complete blood count with platelets, liver transaminases, serum creatinine, and urine protein quantification, as these tests directly assess end-organ damage that determines disease severity and guides delivery timing. 1, 2

Essential Initial Laboratory Tests

Proteinuria Assessment

• Screen with automated dipstick urinalysis; if ≥1+, quantify with spot urine protein/creatinine ratio 1
• Rationale: Proteinuria ≥30 mg/mmol (0.3 mg/mg) confirms renal involvement and is a diagnostic criterion for preeclampsia, though its absence does not exclude the diagnosis 1, 3
• A urine albumin-to-creatinine ratio <30 mg/mmol effectively excludes significant proteinuria 1
• Important caveat: The magnitude of proteinuria does not predict severity or complications and should never be used alone to determine delivery timing 2, 3, 4

Complete Blood Count

• Hemoglobin and hematocrit to assess for hemoconcentration or hemolysis 1, 2
• Platelet count is critical—thrombocytopenia <100,000/μL indicates severe features and progressive decline mandates delivery 1, 2, 3
• Rationale: Platelet consumption reflects endothelial damage and microangiopathic process; progressive thrombocytopenia signals worsening disease requiring immediate delivery regardless of gestational age 1, 2

Liver Function Tests

• Serum transaminases (AST/ALT) to detect hepatocellular injury 1, 2, 3
• Lactate dehydrogenase (LDH) for hemolysis assessment 1
• Rationale: Elevated liver enzymes >2 times upper limit of normal, especially with right upper quadrant or epigastric pain, indicate HELLP syndrome risk and are an indication for delivery 1, 2, 3
• Liver enzyme elevation correlates with acute clinical deterioration and fetal compromise 5

Renal Function Tests

• Serum creatinine to assess kidney function—levels ≥1.1 mg/dL or doubling from baseline indicate severe features 2, 3
• Serum uric acid is associated with worse maternal and fetal outcomes 1, 2
• Rationale: Progressive elevation in creatinine signals acute kidney injury and is a key indicator for delivery 2
• Critical pitfall: Uric acid should never be used alone as an indication for delivery 1, 2

Additional Hemolysis Markers (if HELLP suspected)

• Haptoglobin (decreased in hemolysis) 1
• Peripheral blood smear for schistocytes 1
• Rationale: These confirm microangiopathic hemolytic anemia component of HELLP syndrome, which requires immediate treatment and delivery 1

Monitoring Frequency

Perform laboratory testing at minimum twice weekly (every 3-4 days) for all women with diagnosed preeclampsia 1, 2, 3

• Initial complete panel at diagnosis establishes baseline values 2
• Repeat hemoglobin, platelets, liver enzymes, and creatinine twice weekly if stable 1, 2
• Increase to daily or every 48 hours with clinical deterioration, severe features, or any change in maternal condition 2, 3
• Common pitfall: Inadequate monitoring frequency may miss rapid disease progression—preeclampsia can deteriorate within hours 2, 3

Laboratory-Based Indications for Immediate Delivery

Deliver immediately if any of the following occur, regardless of gestational age 1, 2:

• Progressive thrombocytopenia (declining platelet count) 1, 2
• Progressively abnormal liver enzymes 1, 2
• Worsening renal function (rising creatinine) 1, 2
• Severe hypertension ≥160/110 mmHg unresponsive to three antihypertensive agents 1, 2

Specialized Testing (Not Routine)

Angiogenic Markers

• sFlt-1/PlGF ratio can rule out preeclampsia when <38 in clinically suspected cases 1
• Rationale: Low ratio has strong negative predictive value for short-term absence of preeclampsia 1
• Current recommendation: Not for routine clinical use; should remain within clinical trials 1, 6

Coagulation Studies

• Fibrinogen if DIC suspected or severe HELLP syndrome 1
• Rationale: Assesses for consumptive coagulopathy in severe cases 1

Critical Clinical Pitfalls to Avoid

• Never classify preeclampsia as "mild" versus "severe" clinically—all cases can rapidly become emergencies 1, 2
• Do not use proteinuria levels or uric acid alone to determine delivery timing—these do not predict outcomes 1, 2, 3
• Do not wait for proteinuria to diagnose preeclampsia—approximately 25% of cases lack proteinuria but have other organ dysfunction 3
• Do not dismiss symptoms without severe blood pressure elevation—34% of eclamptic women had diastolic BP ≤100 mmHg 3
• Edema is not diagnostic or predictive—should not be used for diagnosis or severity assessment 3