Is there a diagnostic test for whipple's disease?

See a GI doctor: As it is rare, other diseases should be ruled out first, and then see a GI doctor. Whipple's disease, which most commonly involves small intestine, is diagnosed by taking a biopsy from the lining of the small intestine by using an upper endoscopy. if the tissue sample show macrophages positive for periodic acid-schiff stain, the electron microscopy and then dna testing can confirm the diagnosis.

Biopsy: Best test is to biopsy an actively involved site. Whipples is rare and other much more common causes of GI symptoms / arthritis and neurologic symptoms must be ruled out.