A 33-year-old primigravida at 36 weeks gestation is brought to the emergency department by… — USMLE Step 3

A 33-year-old primigravida at 36 weeks gestation is brought to the emergency department by her partner due to a 2-day history of progressive nausea, vomiting, and dull right upper quadrant abdominal pain. Over the last 12 hours, she has become increasingly lethargic and confused. Her pregnancy had been uncomplicated until now. Temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $142/88\text{ mmHg}$ , heart rate is $108/\text{min}$ , and respiratory rate is $18/\text{min}$ . Physical examination reveals scleral icterus and a gravid uterus. There is marked tenderness to palpation in the right upper quadrant. Neurological examination shows a somnolent patient who is oriented to person only.

Laboratory studies show:

Test	Result	Reference Range
Hemoglobin	$9.6 \text{ g/dL}$	$12.0-15.5 \text{ g/dL}$
Platelets	$78,000/\mu\text{L}$	$150,000-400,000/\mu\text{L}$
Leukocytes	$15,000/\mu\text{L}$	$4,500-11,000/\mu\text{L}$
Glucose	$42 \text{ mg/dL}$	$70-100 \text{ mg/dL}$
AST	$850 \text{ U/L}$	$8-20 \text{ U/L}$
ALT	$910 \text{ U/L}$	$8-20 \text{ U/L}$
Total bilirubin	$5.2 \text{ mg/dL}$	$0.1-1.0 \text{ mg/dL}$
Creatinine	$1.8 \text{ mg/dL}$	$0.4-1.1 \text{ mg/dL}$
Prothrombin time (PT)	$24 \text{ s}$	$11-14 \text{ s}$
aPTT	$52 \text{ s}$	$25-35 \text{ s}$

Peripheral blood smear shows multiple schistocytes.

Which of the following is the most likely diagnosis?

Acute fatty liver of pregnancyAnswer
B
Hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome
C
Thrombotic thrombocytopenic purpura
D
Acute viral hepatitis
E
Acute cholangitis

Answer

Acute fatty liver of pregnancy

The correct diagnosis is acute fatty liver of pregnancy (AFLP). This condition typically presents in the third trimester with nausea, vomiting, right upper quadrant pain, and jaundice. It is caused by a microvesicular fatty infiltration of hepatocytes that leads to rapidly progressive fulminant liver failure. The key distinguishing features of AFLP, compared to other pregnancy-related liver disorders, are profound hypoglycemia and markedly prolonged coagulation studies (elevated PT and aPTT). These findings reflect the catastrophic loss of hepatic synthetic function. In severe cases, AFLP can be complicated by secondary disseminated intravascular coagulation (DIC), which explains the presence of thrombocytopenia and microangiopathic hemolytic anemia (schistocytes) in this patient.

Step-by-Step Solution

Analyze the patient's clinical presentation.

The patient is a third-trimester pregnant woman with right upper quadrant pain, jaundice, and altered mental status.

Establishing the demographic and primary symptom cluster narrows the differential to third-trimester obstetric emergencies or acute hepatobiliary pathology.

Evaluate the laboratory findings for specific organ involvement.

Labs show severe hypoglycemia, dramatically elevated transaminases, microangiopathic hemolytic anemia (schistocytes), thrombocytopenia, and notably prolonged PT/aPTT.

Identifying the specific pattern of organ failure is required to differentiate overlapping clinical syndromes.

Differentiate between the primary hepatologic conditions of pregnancy using specific biochemical markers.

The profound hypoglycemia and prolonged PT/aPTT indicate fulminant failure of hepatic synthetic function, which is the hallmark differentiator for acute fatty liver of pregnancy (AFLP) over HELLP syndrome.

While HELLP and AFLP both cause hemolysis and low platelets, AFLP is characterized by primary liver synthetic failure, whereas HELLP typically features normal PT/aPTT and glucose unless complicated by severe end-stage DIC.

Key Concept

Differentiating acute fatty liver of pregnancy (AFLP) from HELLP syndrome and other microangiopathies using markers of hepatic synthetic dysfunction (prolonged PT/aPTT and profound hypoglycemia).

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