Rectal biopsy is a diagnostic performed on horses that are suspected of having intestinal disease. It is comparatively less invasive than an intestinal biopsy, which requires exploratory surgery or laparoscopy.
This procedure involves the use of a long biopsy instrument and a gloved arm. The vet passes the instrument through the anus into the rectum. One or more pieces of the rectal lining, the mucosa, are sampled and placed in formalin.
This tissue is sent to a laboratory where it is impregnated with paraffin and then cut into very thin, transparent sections. It is then evaluated under a microscope. The results of this evaluation may be indicative of conditions found in the other parts of the intestinal tract.
Although the results of this test should be evaluated in conjunction with other diagnostics, a complete history, and physical exam, they may be helpful in determining the disease processes going on in the rest of the intestine. Likewise, it is a relatively safe and simple procedure to perform.
Time delay due to off-site evaluation. Not all disease processes in the intestinal tract are reflected in the mucosa of the rectum. For this reason, this test is not always helpful. Since only a tiny piece (or pieces) of the rectum are sampled and evaluated, regional differences in the mucosa may be missed.