Jejunal biopsy is diagnostic in
**Core Concept**
The diagnostic utility of a jejunal biopsy lies in its ability to provide a definitive diagnosis for various gastrointestinal disorders, particularly those affecting the small intestine. This is achieved through the examination of biopsy samples obtained from the jejunum, which can reveal histopathological changes, inflammatory patterns, and other abnormalities.
**Why the Correct Answer is Right**
A jejunal biopsy is diagnostic in Whipple's disease, a rare bacterial infection caused by Tropheryma whipplei. This condition is characterized by malabsorption, weight loss, and diarrhea, and can lead to severe complications if left untreated. The biopsy sample from the jejunum is examined for the presence of periodic acid-Schiff (PAS)-positive macrophages, which contain the bacteria, and other histopathological features. The presence of these characteristic features is diagnostic of Whipple's disease.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because a jejunal biopsy is not diagnostic for celiac disease, which is diagnosed through a combination of clinical assessment, serological tests, and intestinal biopsy. While a jejunal biopsy can provide some information, it is not a definitive diagnostic tool for celiac disease.
* **Option B:** This option is incorrect because a jejunal biopsy is not diagnostic for Crohn's disease, which is diagnosed through a combination of clinical assessment, endoscopic evaluation, and histopathological examination of biopsy samples. While a jejunal biopsy can provide some information, it is not a definitive diagnostic tool for Crohn's disease.
* **Option C:** This option is incorrect because a jejunal biopsy is not diagnostic for giardiasis, which is diagnosed through a combination of clinical assessment, stool examination, and serological tests. While a jejunal biopsy can provide some information, it is not a definitive diagnostic tool for giardiasis.
**Clinical Pearl / High-Yield Fact**
A jejunal biopsy is a valuable diagnostic tool for Whipple's disease, and the presence of PAS-positive macrophages is a key diagnostic feature. This fact highlights the importance of considering Whipple's disease in the differential diagnosis of malabsorption and weight loss.
**Correct Answer: D. Whipple's disease.**