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Difficulty: HardInterpreting Laboratory Results

A 31-year-old primigravida at 36 weeks gestation is brought to the obstetrical triage by her husband due to progressive lethargy, nausea, and severe right upper quadrant abdominal pain over the past 48 hours. She has no significant past medical history, and her prenatal course has been uncomplicated.

Vital signs show a temperature of 37.2°C (99.0°F), blood pressure of 148/92 mm Hg, heart rate of 110/min, and respiratory rate of 18/min. Physical examination reveals scleral icterus and right upper quadrant tenderness without rebound or guarding. The patient is drowsy but arousable and oriented to person and place only.

Laboratory results are as follows:

TestResultReference Range
Sodium136 mEq/L136-145 mEq/L
Potassium4.2 mEq/L3.5-5.0 mEq/L
Bicarbonate18 mEq/L22-28 mEq/L
Blood urea nitrogen38 mg/dL7-18 mg/dL
Creatinine2.1 mg/dL0.6-1.2 mg/dL
Glucose42 mg/dL70-110 mg/dL
Uric acid9.8 mg/dL2.5-6.0 mg/dL
Total bilirubin4.6 mg/dL0.1-1.0 mg/dL
Aspartate aminotransferase (AST)680 U/L10-40 U/L
Alanine aminotransferase (ALT)750 U/L10-40 U/L
Platelets88,000/mm³150,000-400,000/mm³
Prothrombin time (PT)26 sec11-15 sec
Partial thromboplastin time (PTT)58 sec25-40 sec
Fibrinogen115 mg/dL200-400 mg/dL

Based on the interpretation of these laboratory results, which of the following is the most likely diagnosis?

  1. Acute fatty liver of pregnancyAnswer
  2. B
    Hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome
  3. C
    Thrombotic thrombocytopenic purpura
  4. D
    Acute viral hepatitis
  5. E
    Intrahepatic cholestasis of pregnancy

Answer

Acute fatty liver of pregnancy
Acute fatty liver of pregnancy (AFLP) is a microvesicular fatty infiltration of hepatocytes that typically presents in the third trimester. The clinical hallmark is acute hepatic failure, which manifests in laboratory testing as profound hypoglycemia (due to the failure of hepatic gluconeogenesis), coagulopathy (prolonged PT/PTT and low fibrinogen due to the failure of coagulation factor synthesis), and elevated transaminases. The presence of significant hypoglycemia and isolated coagulopathy in this pregnant patient critically distinguishes AFLP from other pregnancy-related liver disorders.

Step-by-Step Solution

1
Identify the primary clinical syndrome from the patient's presentation and vital signs.
The patient is a third-trimester pregnant woman presenting with acute-onset right upper quadrant pain, nausea, lethargy, hypertension, and jaundice.
Establishing the clinical context narrows the differential to third-trimester specific pathologies (e.g., preeclampsia spectrum, acute fatty liver of pregnancy, cholestasis) versus coincidental conditions (e.g., viral hepatitis).
2
Analyze the laboratory panel for evidence of hepatic synthetic dysfunction.
The laboratory results show significant hypoglycemia (glucose 42 mg/dL) and severe coagulopathy (PT 26 sec, PTT 58 sec, fibrinogen 115 mg/dL) alongside moderately elevated transaminases, elevated bilirubin, and acute kidney injury.
Identifying synthetic liver failure (marked by hypoglycemia and decreased production of coagulation factors) is critical for distinguishing the exact etiology among liver-affecting conditions in pregnancy.
3
Synthesize the clinical and laboratory findings to differentiate between HELLP syndrome and Acute fatty liver of pregnancy.
While both conditions can cause thrombocytopenia and elevated transaminases, the profound hypoglycemia and marked prolongation of PT/PTT (without evidence of primary hemorrhage) confirm Acute fatty liver of pregnancy.
HELLP syndrome typically spares hepatic synthetic function (resulting in normal glucose and normal PT/PTT) unless complicated by advanced DIC. The prominent synthetic failure specifically isolates Acute fatty liver of pregnancy as the correct diagnosis.

Key Concept

Differentiating third-trimester hepatic emergencies requires interpreting markers of hepatic synthetic function; profound hypoglycemia and prolonged coagulation times (PT/PTT) strongly indicate Acute Fatty Liver of Pregnancy (AFLP) over HELLP syndrome.
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Interpreting Laboratory Results

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