A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 10-year-old girl is brought to the physician because of high-grade fever, myalgia, and generalized fatigue for 3 days. She returned from a vacation to northern Brazil 4 days ago. She took the appropriate medications and immunizations prior to her visit. There is no family history of serious illness. She appears ill. Her temperature is 39.4°C (103°F), pulse is 110/min and blood pressure is 94/54 mm Hg. Examination shows jaundice of the conjunctivae and skin. The abdomen is soft and nontender; the spleen is palpated 2 to 3 cm below the left costal margin. Laboratory studies show:
Hemoglobin 10.1 g/dL
Leukocyte count 4,650/mm3
Platelet count 200,000/mm3
Serum
Glucose 56 mg/dL
Creatinine 0.8 mg/dL
Bilirubin
Total 4.7 mg/dL
Direct 0.9 mg/dL
Lactate dehydrogenase 212 U/L
Which of the following is the most likely to confirm the diagnosis?"
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A
Thick and thin blood smearCorrect. Thick and thin Giemsa-stained peripheral blood smears are the gold standard for diagnosing malaria — quantify parasitemia and identify species.
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B
Direct antiglobulin testIncorrect. Coombs test diagnoses autoimmune hemolytic anemia — not the cause of hemolysis from intra-erythrocytic parasites.
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C
Sickle cell testIncorrect. Sickle cell testing is for genetic hemoglobinopathies, not for malaria diagnosis (though some hemoglobinopathies protect against P. falciparum).
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D
Ultrasound of the abdomenIncorrect. Abdominal ultrasound documents splenomegaly but provides no etiologic diagnosis; identifying the parasite requires peripheral blood examination.
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E
Bone marrow aspirationIncorrect. Bone marrow aspiration is used for hematologic malignancies, aplastic anemia, and some unexplained cytopenias — it is not the diagnostic test for malaria, which is confirmed by visualizing parasites on peripheral blood smear.
↑ Tap an answer to reveal the reasoning
Answer: A. A 10-year-old with high-grade fever, splenomegaly, hemolytic anemia (Hb 10.1 with indirect hyperbilirubinemia), and a recent return from northern Brazil — a malaria-endemic region — has malaria until proven otherwise. The differential includes Plasmodium falciparum (the most dangerous, with potentially severe cyclical fever, parasitemia, and complications) as well as P. vivax, P. ovale, and P. malariae. "Appropriate medications and immunizations" before travel does not always include effective antimalarial prophylaxis, and even then prophylaxis can fail. The hypoglycemia, jaundice, and high fever raise concern for severe falciparum malaria.
The diagnostic test of choice is a thick and thin peripheral blood smear with Giemsa stain. The thick smear screens for parasitemia (any presence of malaria parasites and rough quantification), while the thin smear is used to identify the species (P. falciparum's banana-shaped gametocytes, ring forms with double chromatin dots, multiple rings per RBC; P. vivax/ovale schüffner stippling; etc.). Three negative thick smears over 12–24 hours are typically required to rule out malaria.
Distractors: Direct antiglobulin (Coombs) test diagnoses autoimmune hemolytic anemia — not malaria. Sickle cell testing is part of pre-travel/sickle cell evaluation but doesn't diagnose acute infection. Abdominal ultrasound documents splenomegaly but does not establish the diagnosis.
Clinical pearl: returned traveler + fever from malaria-endemic area = thick and thin smears (plus rapid diagnostic test if available).
**Why each option:**
**A.** Correct. Thick and thin Giemsa-stained peripheral blood smears are the gold standard for diagnosing malaria — quantify parasitemia and identify species.
**B.** Coombs test diagnoses autoimmune hemolytic anemia — not the cause of hemolysis from intra-erythrocytic parasites.
**C.** Sickle cell testing is for genetic hemoglobinopathies, not for malaria diagnosis (though some hemoglobinopathies protect against P. falciparum).
**D.** Abdominal ultrasound documents splenomegaly but provides no etiologic diagnosis; identifying the parasite requires peripheral blood examination.