A 28-year-old primigravida at 32 weeks gestation presents to the emergency department repo… — USMLE Step 2 CK

A $28$ -year-old primigravida at $32$ weeks gestation presents to the emergency department reporting acute-onset fatigue, shortness of breath, and dark urine for the past $24$ hours. $3$ days ago, she was diagnosed with an uncomplicated urinary tract infection and prescribed nitrofurantoin. Her prenatal course has otherwise been unremarkable.

Temperature is $37.4^\circ\text{C}$ ( $99.3^\circ\text{F}$ ), blood pressure is $110/70$ mmHg, pulse is $112$ /min, and respirations are $20$ /min. Physical examination reveals conjunctival pallor and mild scleral icterus. The uterine fundus is consistent with gestational age. Continuous fetal heart rate monitoring demonstrates a baseline of $165$ /min, minimal variability, and occasional variable decelerations.

Laboratory studies show:

Test	Result	Reference Range
Hemoglobin	$6.8$ g/dL	$11.0$ - $14.0$ g/dL
Platelets	$185,000/\mu\text{L}$	$150,000$ - $400,000/\mu\text{L}$
Leukocytes	$9,500/\mu\text{L}$	$4,500$ - $11,000/\mu\text{L}$
Mean corpuscular volume	$94$ fL	$80$ - $100$ fL
Lactate dehydrogenase	$840$ U/L	$100$ - $250$ U/L
Total bilirubin	$4.5$ mg/dL	$0.1$ - $1.2$ mg/dL
Direct bilirubin	$0.5$ mg/dL	$0.0$ - $0.3$ mg/dL
Aspartate aminotransferase	$25$ U/L	$10$ - $40$ U/L
Alanine aminotransferase	$22$ U/L	$7$ - $56$ U/L
Creatinine	$0.7$ mg/dL	$0.5$ - $1.1$ mg/dL

A peripheral blood smear stained with Wright-Giemsa is obtained (see image) and reveals scattered erythrocytes with irregular, semi-circular marginal defects.

Which of the following is the most appropriate next step in management?

A
Initiate intravenous piperacillin-tazobactam and admit to the intensive care unit
B
Reassure the patient and prescribe oral iron supplementation for physiologic anemia
Discontinue the current antibiotic and prepare for packed red blood cell transfusionAnswer
D
Proceed directly to emergent cesarean delivery for non-reassuring fetal status
E
Order a comprehensive thyroid panel including thyroid-stimulating hormone

Answer

Discontinue the current antibiotic and prepare for packed red blood cell transfusion.

The correct answer involves discontinuing the offending medication and providing a blood transfusion. The patient is experiencing acute hemolytic anemia due to Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency, triggered by the recent initiation of nitrofurantoin. This is evidenced by her acute drop in hemoglobin, elevated indirect bilirubin, elevated lactate dehydrogenase, and the classic peripheral smear finding of degmacytes (bite cells). In G6PD deficiency, oxidative stress causes hemoglobin to denature into Heinz bodies, which are subsequently 'bitten' out by splenic macrophages. The symptomatic anemia (tachycardia, dyspnea) and non-reassuring fetal status are secondary to decreased maternal oxygen carrying capacity. The most appropriate next step is to stop the offending agent and provide a blood transfusion to restore oxygen delivery, which simultaneously acts as intrauterine resuscitation for the fetus.

Step-by-Step Solution

Analyze the clinical presentation and laboratory data to identify the primary pathophysiologic process.

The patient has acute severe normocytic anemia, elevated lactate dehydrogenase, indirect hyperbilirubinemia, and hemoglobinuria (dark urine), indicating an acute hemolytic crisis.

Recognizing the presence of active hemolysis is the critical first step before determining the specific etiology.

Correlate the hemolytic crisis with the patient's recent medical history and peripheral smear findings.

The recent initiation of nitrofurantoin combined with the presence of degmacytes (bite cells) on the peripheral smear confirms oxidative stress-induced hemolysis, which is characteristic of Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency.

Identifying the specific trigger is necessary to halt the disease process and guide targeted management.

Evaluate the maternal and fetal clinical status to determine the urgency and type of intervention required.

The mother is symptomatic (tachycardia, dyspnea) with a critically low hemoglobin of

6.8

g/dL, leading to secondary fetal compromise (fetal tachycardia, minimal variability).

Fetal distress in this context is secondary to maternal hypoxia; thus, maternal resuscitation is the absolute priority.

Select the most appropriate definitive management.

Discontinue the oxidative drug (nitrofurantoin) and administer a packed red blood cell transfusion to correct the oxygen-carrying deficit.

Stopping the offending agent halts further hemolysis, while a blood transfusion treats the severe symptomatic anemia and serves as effective intrauterine resuscitation.

Key Concept

Diagnosis and management of acute hemolytic anemia due to Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency, including the recognition of oxidative triggers and the provision of appropriate supportive care.

Estimated Time:2m 0s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic