Regurgitation occurs when there is either an anatomic obstruction or a physiologic weakness in the esophagus. In either case, food is retained in the esophagus and, if it passively migrates back into the oropharynx, can be regurgitated. The problem should be diagnosed quickly in an attempt to solve it before the esophagus becomes irreversibly-dilated or the patient experiences an aspiration pneumonia.
Chronic diarrhea (i.e., that which persists > 2-3 weeks) usually necessitates a systematic diagnostic approach (which may mean classic tests and/or therapeutic trials). The first question in the patient with chronic diarrhea is whether the patient has an obvious problem such as parasites or an obviously inadequate or poor quality diet.
Once maldigestion is eliminated, then malabsorptive diseases must be considered. Malabsorptive small intestinal disease is a common cause of diarrhea. However, a substantial number of dogs (and cats) with malabsorptive small intestinal disease have normal stools despite severe intestinal pathology.
When concerned with protein loss of any cause, one should measure serum albumin concentrations (NOT serum total protein concentrations). Do not use human clinical pathology laboratories as their technology typically does not detect canine albumin (meaning that they routinely report serum albumin concentrations of < 1.5 gm/dl in clinically normal dogs).
Hematemesis necessitates a slightly different approach than we take with other vomiting cases because some rule-outs become more likely while others become much less likely. We will be including upper gastrointestinal bleeding of any cause in this discussion.
Congenital portosystemic shunts (PSS) are much more common and certainly much more confusing than we ever imagined. At Texas A&M, we infrequently see the "classic" congenital PSS with the relatively straight forward presentation (i.e., young Yorkie with post prandial hepatic encephalopathy), probably because those cases are efficiently filtered out and never referred to us.
Intestinal biopsy may be accomplished two ways: endoscopy and surgery. CBC, serum chemistry profile, and urinalysis are useful and may point out systemic manifestations of the disease which will aid in correctly diagnosing and prognosing the problem (e.g., hypoalbuminemia due to histoplasmosis), but are also useful as a preanesthetic work up before endoscopy.