Diagnostic Criteria for Acute Fatty Liver of Pregnancy
The diagnosis of acute fatty liver of pregnancy (AFLP) is established using the Swansea criteria, which requires the presence of 6 or more of 14 clinical and laboratory features in the absence of another explanation for liver dysfunction.
The Swansea Criteria
The Swansea criteria include the following 14 parameters 1, 2:
Clinical Features:
- Vomiting
- Abdominal pain
- Polydipsia/polyuria
- Encephalopathy
Laboratory Parameters:
- Hypoglycemia (blood glucose <72 mg/dL)
- Elevated aminotransferases (ALT or AST typically <500 U/L)
- Elevated bilirubin (usually <5 mg/dL)
- Hyperammonemia
- Elevated uric acid
- Leukocytosis (WBC >11 × 10⁶/L)
- Elevated creatinine or acute kidney injury
- Coagulopathy (prolonged PT >14 seconds or APTT >34 seconds)
- Thrombocytopenia (though notably, approximately 50% of AFLP patients do NOT have thrombocytopenia at presentation 3)
- Ascites or bright liver on imaging (fatty infiltration on CT or ultrasound)
Key Diagnostic Considerations
Timing and Presentation
AFLP typically presents in the third trimester or postpartum period 1. The condition occurs in approximately 0.01% of pregnancies and is associated with multiparity, multifetal pregnancy, and male fetus 1.
Critical Distinguishing Features
When differentiating AFLP from HELLP syndrome, several features are particularly helpful 1, 3:
- Hypertension: HELLP syndrome is typically associated with pre-eclampsia and hypertension, while AFLP often occurs in the absence of hypertension
- Hypoglycemia and hyperammonemia: These metabolic derangements are characteristic of AFLP and serve as critical diagnostic indicators 4, 5
- Disseminated intravascular coagulation (DIC): Present in >75% of AFLP cases but less common in HELLP 1
- Antithrombin deficiency: AFLP is exclusively associated with pregnancy-induced antithrombin deficiency (AT activity <65%), which is not included in the Swansea criteria but may facilitate earlier diagnosis 3
Imaging Findings
- CT scan: Decreased hepatic attenuation (CT value around 23 Hounsfield units) suggesting fatty deposition 6
- Ultrasound: May show fatty infiltration, sometimes with ascites 1
- Important caveat: Controlled attenuation parameter (CAP) by transient elastography may underestimate hepatic fat in AFLP because the steatosis is predominantly microvesicular rather than macrovesicular 6
Practical Diagnostic Algorithm
For early suspicion and diagnosis, a simplified model has been validated with 97.6% sensitivity and 97.1% specificity 7:
- Gastrointestinal symptoms (vomiting, abdominal pain)
- Elevated aminotransferases (>42 IU/L)
- Elevated bilirubin (>0.8 mg/dL)
- Elevated bile acids (>10.0 μmol/L)
- Prolonged coagulation (APTT >34s or PT >14s)
This combination allows for earlier identification before progression to life-threatening complications.
Severity Assessment
Patients scoring >7 on the Swansea criteria should be considered for intensive care admission 8. Additional indicators of severe disease requiring ICU-level care include:
- Encephalopathy
- Elevated serum lactate (>2.8 mg/dL)
- MELD score >30
- Multiorgan dysfunction including DIC and acute kidney injury requiring renal replacement therapy 4
Important Caveats
- The Swansea criteria have limitations in differentiating AFLP from other causes of acute liver failure and pregnancy-related liver diseases 1
- Approximately 50% of AFLP patients do not have thrombocytopenia at presentation, so its absence should not exclude the diagnosis 3
- The diagnosis should be made clinically and biochemically; liver biopsy is not required for diagnosis but may be confirmatory in atypical cases, showing characteristic microvesicular steatosis 6, 9
- Early recognition is critical as delay in diagnosis has life-threatening consequences for both mother and fetus 2
Once AFLP is diagnosed, delivery should be expedited after stabilization of coagulopathy and metabolic derangements, as prompt delivery is the definitive treatment 8, 4, 5.