What laboratory tests are indicated for a pregnant woman presenting with abdominal pain?

Laboratory Tests for Abdominal Pain in Pregnancy

For pregnant women presenting with abdominal pain, ultrasound should be the first imaging test, followed by laboratory tests including complete blood count, liver enzymes, renal function tests, electrolytes, C-reactive protein, and serum lactate, with additional specialized tests based on clinical suspicion. 1

Initial Laboratory Evaluation

All pregnant women with abdominal pain should undergo the following basic laboratory tests:

• Pregnancy test (β-hCG) - Essential to confirm pregnancy status and rule out ectopic pregnancy 1, 2
• Complete blood count (CBC) - To assess for leukocytosis, anemia, or thrombocytopenia 1
• Comprehensive metabolic panel:
  • Electrolytes - To evaluate for electrolyte imbalances 1
  • Liver function tests - ALT, AST, bilirubin, alkaline phosphatase 1
  • Renal function tests - BUN, creatinine 1
  • Serum albumin - To assess nutritional status and liver function 1
• Inflammatory markers:
  • C-reactive protein (CRP) - Elevated in inflammatory conditions 1
  • Procalcitonin - More specific for bacterial infections 1
• Serum lactate - To assess for tissue hypoperfusion 1
• Urinalysis - To evaluate for urinary tract infection or proteinuria 2

Condition-Specific Laboratory Tests

Based on clinical presentation and initial findings, consider these additional tests:

For Suspected Liver Disease in Pregnancy

• Serum bile acids - Elevated (>10 μmol/L) in intrahepatic cholestasis of pregnancy 1
• Coagulation studies (PT/INR, PTT) - Abnormal in HELLP syndrome and acute fatty liver of pregnancy 1
• Platelet count - Low in HELLP syndrome (<150 × 10^9/L) 1
• LDH - Elevated in HELLP syndrome and hemolysis 1

For Suspected Infection or Abscess

• Blood cultures - If fever or sepsis is suspected 1
• Amylase/lipase - To evaluate for pancreatitis 2

For Suspected Nutritional Deficiencies (Post-Bariatric Surgery)

• Vitamin levels - Vitamin D, B12, B6, B1, and folate 1

Imaging Considerations

Laboratory tests should be complemented by appropriate imaging:

• Ultrasound - First-line imaging for pregnant women with abdominal pain (sensitivity 96.7%, specificity 85.7%) 1, 2
• MRI without contrast - When ultrasound is inconclusive (rated 7/9 for appropriateness) 1
• CT with contrast - Only after other non-radiation studies have been exhausted (rated 5/9 for appropriateness) 1

Diagnostic Algorithm for Specific Conditions

1. Right upper quadrant pain:

   • CBC, liver enzymes, bile acids
   • Consider ultrasound for gallbladder pathology
   • If hyperemesis gravidarum is suspected, check electrolytes and ketones 1

2. Right lower quadrant pain:

   • CBC, CRP
   • Pelvic ultrasound to evaluate for appendicitis vs. ovarian pathology 1
   • Consider MRI if ultrasound inconclusive 1

3. Diffuse abdominal pain with hypertension:

   • CBC with platelet count, liver enzymes, uric acid, LDH
   • Urinalysis for proteinuria
   • Consider HELLP syndrome or preeclampsia 1

4. Diffuse abdominal pain with jaundice:

   • Complete liver panel, coagulation studies, glucose
   • Consider acute fatty liver of pregnancy 1

Common Pitfalls to Avoid

• Relying solely on laboratory tests without appropriate imaging can lead to missed diagnoses 2
• Dismissing abnormal liver enzymes as pregnancy-related without considering pregnancy-specific liver diseases 1
• Failing to consider gynecologic causes of abdominal pain (ectopic pregnancy, ovarian torsion) 2, 3
• Overlooking the anatomical changes of pregnancy that can alter the presentation of common conditions like appendicitis 3, 4

Remember that pregnancy alters normal laboratory values and can mask or mimic various conditions. A systematic approach combining laboratory tests, imaging, and clinical assessment is essential for accurate diagnosis.