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Zorluk: OrtaOrdering Laboratory Tests

A 34-year-old woman presents to the primary care clinic reporting a 6-month history of fatigue, loose non-bloody stools, and occasional abdominal bloating. She has a medical history of Hashimoto thyroiditis for which she takes levothyroxine. Vital signs are within normal limits. Physical examination reveals pale conjunctivae and mild abdominal distension but is otherwise unremarkable. Initial laboratory studies show a hemoglobin of 10.4 g/dL, a mean corpuscular volume of 74 fL, and a low serum ferritin level. A comprehensive metabolic panel is unremarkable. Given the suspected diagnosis, which of the following is the most appropriate next step in laboratory evaluation?

  1. IgA anti-tissue transglutaminase antibody and total serum IgACevap
  2. B
    IgA anti-tissue transglutaminase antibody alone
  3. C
    IgG anti-deamidated gliadin peptide antibody
  4. D
    HLA-DQ2 and HLA-DQ8 genotyping
  5. E
    Fecal calprotectin level

Cevap

The most appropriate initial laboratory evaluation is ordering an IgA anti-tissue transglutaminase antibody along with a total serum IgA level.
This patient's presentation of chronic diarrhea, iron deficiency anemia (microcytic anemia with low ferritin), and concurrent autoimmune disease (Hashimoto thyroiditis) is highly characteristic of celiac disease. The most appropriate initial, non-invasive screening approach is measuring the IgA anti-tissue transglutaminase (tTG) antibody. However, because selective IgA deficiency is up to 10 to 15 times more prevalent in patients with celiac disease than in the general population, a total serum IgA level must be measured simultaneously. If the patient is IgA deficient, the IgA tTG antibody will be falsely negative. In such cases, the diagnostic sequence must shift to IgG-based testing, such as the IgG deamidated gliadin peptide (DGP) antibody.

Adım Adım Çözüm

1
Identify the primary clinical syndrome.
The patient has chronic diarrhea, iron deficiency anemia, and a history of another autoimmune condition (Hashimoto thyroiditis).
Recognizing this triad strongly points toward celiac disease as the unifying diagnosis.
2
Determine the preferred initial diagnostic test for the suspected condition.
IgA anti-tissue transglutaminase (tTG) antibody is the most sensitive and specific initial serologic test.
Current guidelines recommend IgA tTG as the first-line screening test for celiac disease.
3
Identify any necessary concurrent testing required to validate the primary test.
A total serum IgA level must be ordered simultaneously.
Selective IgA deficiency is common in patients with celiac disease. If the patient is IgA deficient, the IgA tTG will be falsely negative, necessitating alternative testing (e.g., IgG-based testing).

Anahtar Kavram

In patients with suspected celiac disease, initial serologic screening requires both IgA anti-tissue transglutaminase (tTG) antibody and a total serum IgA level to prevent false-negative results in the setting of selective IgA deficiency.
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Ordering Laboratory Tests

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