Emergency medical services bring a primigravid patient at 34 weeks gestation to the obstet… — USMLE Step 3

Emergency medical services bring a primigravid patient at $34$ weeks gestation to the obstetric triage unit after she developed acute, severe right upper quadrant abdominal pain and recurrent vomiting. Her blood pressure is $162/98$ mm Hg, and her pulse is $94$ /min. Physical examination demonstrates marked tenderness just below the right costal margin. Laboratory studies reveal the following:

Test	Result	Reference Range
Hemoglobin	$8.9$ g/dL	$11.0-14.0$ g/dL
Platelets	$52,000$ /mm³	$150,000-400,000$ /mm³
Aspartate aminotransferase (AST)	$285$ U/L	$10-40$ U/L
Alanine aminotransferase (ALT)	$290$ U/L	$10-40$ U/L
Total bilirubin	$2.4$ mg/dL	$0.2-1.2$ mg/dL
Prothrombin time (PT)	$12.5$ sec	$11-15$ sec
Activated partial thromboplastin time (aPTT)	$32$ sec	$25-40$ sec
Fibrinogen	$420$ mg/dL	$300-600$ mg/dL (in pregnancy)

A peripheral blood smear demonstrates numerous schistocytes.

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

A
Acute fatty liver of pregnancy
B
Disseminated intravascular coagulation
HELLP syndromeAnswer
D
Immune thrombocytopenia
E
Thrombotic thrombocytopenic purpura

Answer

HELLP syndrome

The correct answer accurately identifies HELLP syndrome, which is defined by the triad of Hemolysis (evidenced by anemia, schistocytes, and elevated bilirubin), Elevated Liver enzymes (transaminitis), and Low Platelets. A critical distinguishing factor in interpreting laboratory results for HELLP is that, unlike disseminated intravascular coagulation (DIC) or acute fatty liver of pregnancy (AFLP), the coagulation studies (PT, aPTT, and fibrinogen) remain completely normal until catastrophic complications (such as liver rupture or secondary DIC) occur.

Step-by-Step Solution

Identify the signs of microangiopathic hemolytic anemia (MAHA) and liver involvement.

The patient has anemia, schistocytes, and elevated indirect bilirubin (hemolysis), along with elevated AST/ALT and low platelets.

These findings establish the classic triad of Hemolysis, Elevated Liver enzymes, and Low Platelets.

Evaluate the coagulation cascade laboratory results (PT, aPTT, fibrinogen).

The PT, aPTT, and fibrinogen levels are all within normal reference ranges.

Normal coagulation studies are critical to exclude consumptive coagulopathies and severe synthetic liver failure.

Synthesize the laboratory data with the clinical context to determine the diagnosis.

A third-trimester pregnant patient with MAHA, transaminitis, thrombocytopenia, and normal coagulation studies most likely has HELLP syndrome.

This specific laboratory profile successfully differentiates HELLP from acute fatty liver of pregnancy (AFLP) and disseminated intravascular coagulation (DIC).

Key Concept

Distinguishing microangiopathic hemolytic anemias and liver pathologies in pregnancy primarily relies on interpreting the coagulation profile (PT, aPTT, fibrinogen) alongside basic metabolic and hematologic markers.

Estimated Time:1m 30s

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