What is the diagnostic approach for acute fatty liver of pregnancy (AFLP)?

Diagnostic Approach to Acute Fatty Liver of Pregnancy

Diagnose AFLP using the Swansea criteria: the presence of 6 or more specific clinical and laboratory findings in a third-trimester or postpartum patient, in the absence of another cause, establishes the diagnosis without requiring liver biopsy. 1

Clinical Presentation and Timing

AFLP occurs almost exclusively in the third trimester (week 29 and beyond) or rarely postpartum, distinguishing it from other pregnancy-related liver diseases. 1

Key presenting symptoms include:

• Nausea and vomiting (88.5% of cases) 2
• Jaundice (71.4% of cases) 2
• Right upper quadrant or epigastric pain (51.4% of cases) 2
• Malaise and headache 1
• Hepatic encephalopathy (if present, highly suspicious for AFLP over HELLP syndrome) 1

The Swansea Criteria for Diagnosis

The diagnosis requires 6 or more of the following findings in the absence of another explanation: 1

• Vomiting
• Abdominal pain
• Polydipsia/polyuria
• Encephalopathy
• Elevated transaminases (AST or ALT >42 IU/L) 1
• Elevated bilirubin (>0.8 mg/dL) 1
• Hypoglycemia (<72 mg/dL) - characteristic feature that helps differentiate from HELLP 1, 3
• Leukocytosis (>11 × 10⁶/L) 1
• Elevated uric acid (>5.7 mg/dL) 1
• Elevated ammonia (>42 IU/L) 1
• Ascites or bright liver on ultrasound 1
• Renal impairment (creatinine >1.7 mg/dL) 1, 4
• Coagulopathy (prolonged PT, reduced fibrinogen) 1, 4

Essential Laboratory Evaluation

Order the following tests immediately when AFLP is suspected: 1

• Complete blood count with peripheral smear (to assess for hemolysis and differentiate from HELLP) 4
• Comprehensive metabolic panel including liver enzymes, bilirubin, and renal function 2
• Coagulation studies (PT/PTT, fibrinogen) - prolonged PT and low fibrinogen suggest AFLP over HELLP 1, 4
• Glucose levels (monitor every 2-4 hours if AFLP suspected due to high risk of hypoglycemia) 3
• Lactate dehydrogenase (markedly elevated, often >500 U/L) 4
• Ammonia level 1
• Uric acid 1

Critical distinguishing features from HELLP syndrome: 1, 4

• AFLP: Prolonged PT, low fibrinogen, hypoglycemia common, encephalopathy may occur
• HELLP: Normal PT initially, fibrinogen normal/elevated, hypoglycemia rare, encephalopathy uncommon

Imaging Approach

Abdominal ultrasound without Doppler is the first-line imaging modality given lack of ionizing radiation and absence of known fetal risks. 1

• Look for bright liver (increased echogenicity) or fatty infiltration 1, 5
• Assess for ascites 1
• Rule out biliary obstruction 6

If further imaging is needed, MRI without gadolinium is preferred over CT in all trimesters. 1 Gadolinium should be avoided as it crosses the placenta and accumulates in fetal urinary tract. 1

When to Suspect AFLP: The "AFLP Triad"

A practical clinical approach identifies three components: 2

1. Symptoms triad: Nausea/vomiting + jaundice + epigastric pain
2. Laboratory triad: Renal dysfunction + coagulopathy + liver function abnormalities with hypoglycemia
3. Complications triad: Renal failure + coagulopathy + ascites ± encephalopathy

Critical Severity Assessment

The following findings indicate need for ICU-level care and potential transplant evaluation: 1, 3

• Encephalopathy development 1
• Elevated serum lactate (>2.8 mg/dL) 1
• MELD score >30 1
• Swansea criteria score >7 1

Common Diagnostic Pitfalls

Liver biopsy is rarely indicated and not advised - diagnosis can usually be determined clinically without biopsy. 1, 7 The risks of biopsy in the setting of coagulopathy outweigh benefits when clinical criteria are sufficient.

Do not delay diagnosis waiting for imaging confirmation - ultrasound may show enhanced echo or fatty liver in only 73% of cases. 5 Clinical and laboratory criteria take precedence.

Screen newborns for LCHAD deficiency (long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency), as there is a strong association between fetal LCHAD deficiency and maternal AFLP. 1 These newborns require genetic counseling and dietary modifications to prevent metabolic crises and death within the first year. 1

Differential Diagnosis Considerations

Evaluate for other pregnancy-specific liver diseases based on gestational timing: 1

• HELLP syndrome: Weeks 27-37, hemolysis with schistocytes, thrombocytopenia <100 × 10⁹/L, normal PT/fibrinogen initially 4
• Preeclampsia: After 20 weeks, hypertension and proteinuria predominate 1
• Intrahepatic cholestasis of pregnancy: After 30 weeks, pruritus with elevated bile acids but normal PT 1

Any elevation in aminotransferases, bilirubin, or bile acids in pregnancy is abnormal and requires investigation - these values should remain normal throughout all trimesters. 1