**Core Concept**
Celiac disease is an autoimmune disorder characterized by small intestine mucosal damage in response to gluten consumption. Diagnosis involves serological tests, intestinal biopsy, and clinical evaluation.

**Why the Correct Answer is Right**
Serological tests for celiac disease include tissue transglutaminase antibody (tTGA), endomysial antibody (EMA), and gliadin antibody (AGA). These tests detect the presence of autoantibodies against tissue transglutaminase, which is a key enzyme involved in gluten processing. Intestinal biopsy, specifically the assessment of small intestine mucosal villous atrophy, is a definitive diagnostic tool. Clinical evaluation involves a detailed medical history, physical examination, and exclusion of other causes of malabsorption.

**Why Each Wrong Option is Incorrect**
**Option A:** Tissue transglutaminase antibody (tTGA) is used for diagnosing celiac disease.
**Option B:** Endomysial antibody (EMA) is also used for diagnosing celiac disease.
**Option C:** Gliadin antibody (AGA) is sometimes used for diagnosing celiac disease, although it is less specific than tTGA or EMA.

**Clinical Pearl / High-Yield Fact**
The key to diagnosing celiac disease is a combination of serological tests, intestinal biopsy, and clinical evaluation. A positive serological test result and characteristic intestinal biopsy findings, along with a clinical presentation consistent with malabsorption, are essential for establishing a diagnosis.

**Correct Answer:** D.