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Difficulty: EasyGastroenterology and Hepatology

A 32-year-old woman presents to the clinic complaining of a 66-month history of fatigue, abdominal bloating, and frequent, bulky, foul-smelling bowel movements. She has not traveled recently and reports no blood in her stool. Her past medical history is notable for type 1 diabetes mellitus. Vital signs are within normal limits. Physical examination reveals mild conjunctival pallor but is otherwise unremarkable. Laboratory studies show a hemoglobin of 10.4 g/dL10.4 \text{ g/dL} and a mean corpuscular volume of 74 fL74 \text{ fL}. Which of the following is the most appropriate next step in diagnosis?

  1. Measurement of serum tissue transglutaminase IgA and total IgA levelsAnswer
  2. B
    Empiric initiation of a gluten-free diet
  3. C
    Empiric administration of oral ciprofloxacin
  4. D
    Measurement of serum thyroid-stimulating hormone
  5. E
    Colonoscopy with random mucosal biopsies

Answer

The most appropriate next step in diagnosis is the measurement of serum tissue transglutaminase IgA and total IgA levels.
This patient's chronic osmotic diarrhea, bloating, and iron deficiency anemia (microcytosis with pallor), especially in the context of another autoimmune disease (type 1 diabetes mellitus), strongly suggest celiac disease. The best initial diagnostic step is serologic testing with IgA anti-tissue transglutaminase (tTG-IgA) antibodies. A total IgA level must be checked simultaneously because selective IgA deficiency is common in patients with celiac disease; if the patient is IgA deficient, IgG-based testing (like deamidated gliadin peptide IgG) is required to avoid a false negative.

Step-by-Step Solution

1
Analyze the clinical presentation.
The patient has chronic osmotic diarrhea, iron deficiency anemia, and a history of type 1 diabetes mellitus.
Identifying the classic symptom triad of malabsorption alongside an autoimmune history raises the pretest probability for celiac disease.
2
Determine the preferred initial diagnostic algorithm for the suspected condition.
Initial screening for celiac disease should be non-invasive serologic testing.
Serology is highly sensitive and specific, avoiding unnecessary early invasive procedures.
3
Select the most accurate serologic test.
Tissue transglutaminase IgA (tTG-IgA) paired with total IgA is chosen.
tTG-IgA is the most sensitive and specific initial test. Total IgA must be measured concurrently to rule out selective IgA deficiency, which would cause a false-negative tTG-IgA result.

Key Concept

Initial evaluation of suspected celiac disease requires measurement of serum tissue transglutaminase IgA (tTG-IgA) and total IgA levels while the patient is consuming a gluten-containing diet.
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Topics

Gastroenterology and Hepatology

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