A 26-year-old woman, G1P0, at 16 weeks gestation is evaluated during a routine prenatal vi… — USMLE Step 2 CK

A 26-year-old woman, G1P0, at 16 weeks gestation is evaluated during a routine prenatal visit. She reports mild fatigue over the past month but is otherwise feeling well. She has no significant past medical history. Current medications include a daily prenatal vitamin.

Vital signs are within normal limits. Physical examination reveals normal conjunctivae, no scleral icterus, and a gravid uterus consistent with gestational age.

Laboratory results are as follows:

Test	Result	Reference Range
Hemoglobin	$10.1\text{ g/dL}$	$12.0-15.5\text{ g/dL}$
Mean corpuscular volume (MCV)	$65\text{ fL}$	$80-100\text{ fL}$
Red blood cell (RBC) count	$5.8\text{ million/}\mu\text{L}$	$4.1-5.1\text{ million/}\mu\text{L}$
Platelets	$250,000\text{/}\mu\text{L}$	$150,000-400,000\text{/}\mu\text{L}$
Leukocytes	$8,500\text{/}\mu\text{L}$	$4,500-11,000\text{/}\mu\text{L}$
Serum iron	$95\text{ }\mu\text{g/dL}$	$60-170\text{ }\mu\text{g/dL}$
Total iron-binding capacity (TIBC)	$310\text{ }\mu\text{g/dL}$	$240-450\text{ }\mu\text{g/dL}$
Ferritin	$180\text{ ng/mL}$	$12-150\text{ ng/mL}$

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

Hemoglobin electrophoresisCevap
B
Reassurance and continuation of routine prenatal care
C
Initiate oral ferrous sulfate therapy
D
Measure serum folate and vitamin B12 levels
E
Schedule a bone marrow aspiration

Cevap

The most appropriate next step is to perform hemoglobin electrophoresis to evaluate for thalassemia trait.

The patient presents with a profoundly microcytic anemia (MCV 65 fL) but has normal iron studies, including a ferritin level of 180 ng/mL, which effectively rules out iron deficiency. Furthermore, her red blood cell (RBC) count is elevated despite the low hemoglobin, yielding a Mentzer index (MCV/RBC count) of less than 13. This combination of severe microcytosis, an elevated RBC count, and normal to high iron stores is the classic presentation of thalassemia minor (trait). The definitive next step in management to confirm this diagnosis is hemoglobin electrophoresis, which typically demonstrates an elevated hemoglobin A2 fraction in beta-thalassemia trait.

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Analyze the complete blood count (CBC) results.

The patient has mild anemia (Hemoglobin 10.1 g/dL) with profound microcytosis (MCV 65 fL) and an elevated RBC count (5.8 million/µL).

To classify the morphology of the anemia based on red blood cell indices.

Evaluate the iron panel to distinguish the etiology of the microcytosis.

Serum iron, TIBC, and ferritin are all within or slightly above normal limits.

To rule out iron deficiency, which is the most common cause of microcytic anemia in pregnancy.

Synthesize findings to determine the most likely diagnosis.

Microcytic anemia with normal iron stores and an elevated RBC count (yielding a Mentzer index < 13) strongly suggests thalassemia minor (trait).

Differentiating between causes of microcytosis directs the next diagnostic or therapeutic step.

Select the appropriate diagnostic confirmation test.

Hemoglobin electrophoresis is indicated.

Electrophoresis separates hemoglobins and identifies abnormal variants or altered proportions (e.g., elevated HbA2 in beta-thalassemia trait).

Anahtar Kavram

Patients presenting with microcytic anemia, an elevated red blood cell count, and normal iron studies (normal or elevated ferritin) should be evaluated for thalassemia trait using hemoglobin electrophoresis.

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