What test should be ordered to support the diagnosis of celiac disease in a patient with severe anemia?

Diagnostic Testing for Celiac Disease in a Patient with Severe Anemia

The AG-ACNP should order Immunoglobulin A tissue transglutaminase (IgA-tTG) antibody test to support the diagnosis of celiac disease in this patient with severe anemia. 1

Primary Diagnostic Testing

• IgA anti-tissue transglutaminase (IgA-tTG) is the preferred initial test for diagnosing celiac disease in patients older than two years 1

  • Sensitivity: 90-96% in adults
  • Specificity: 87.4% in adults 2
  • Must be performed before initiating a gluten-free diet to maintain accuracy 1

• Total IgA level should be measured simultaneously to rule out IgA deficiency, which is 10-15 times more common in celiac patients 2

  • If IgA deficiency is detected, IgG-based testing should be performed instead 1, 2

Additional Testing Considerations

For Patients with High Clinical Suspicion

If clinical suspicion remains high despite negative serological results:

• Proceed with duodenal biopsy via upper endoscopy 1
• Consider HLA-DQ2/DQ8 testing (negative result has ~100% negative predictive value) 2

Laboratory Variability

• Significant variability exists between commercial laboratories in test characteristics 3
  • Sensitivity ranges from 40.0% to 86.4% between different labs
  • Specificity ranges from 41.7% to 100.0% 3
• Validation against biopsy results within a practice is recommended 1

Addressing the Patient's Anemia

The patient's severe anemia (hemoglobin 6.8) is likely related to celiac disease, as iron deficiency anemia is a common extraintestinal manifestation. While blood transfusion may be necessary for symptomatic anemia, it doesn't address the underlying cause.

After Confirming Diagnosis

Once celiac disease is confirmed:

1. Evaluate for nutritional deficiencies (iron, folate, B12, vitamin D)
2. Implement a strict gluten-free diet under nutritionist supervision
3. Monitor response with follow-up serological testing at 6 and 12 months 2

Common Pitfalls to Avoid

1. Don't start a gluten-free diet before testing - This can lead to false-negative results 1
2. Don't rely solely on symptoms - Gastrointestinal symptoms alone cannot accurately differentiate celiac disease from other disorders 1
3. Don't overlook IgA deficiency - Always check total IgA or perform simultaneous IgG testing 1, 2
4. Don't miss partial villous atrophy - The sensitivity of tTG-IgA is significantly lower (42.3%) in patients with partial villous atrophy compared to total villous atrophy (90.0%) 3

By following this diagnostic approach, the AG-ACNP can properly evaluate for celiac disease while managing the patient's acute presentation of pneumonia and dehydration.