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Diagnosis of Diarrhea


History

The physician should find out from the patient an accurate description of the nature of the diarrhea: the duration, frequency, consistency, volume, color, and relation to meals. Also, it is important to determine the presence of any underlying illnesses or systemic symptoms and to establish the patient’s recent travel history, use of medications or drugs, and sexual preferences.

The history can help to determine whether the pathology is in the small or large bowel. If the stools are large, watery, soupy, or greasy, possibly containing undigested food particles, the disorder is most likely in the small intestine. There may be accompanying periumbilical or right lower quadrant pain or intermittent, crampy abdominal pain.

If the disease is in the descending colon or rectum, the patient usually passes small quantities of stool or mucus frequently. The stools are usually mushy and brown, and sometimes mixed with mucus and blood. There may be a sense of urgency and tenesmus. If there is pain, it is usually achy and located in the lower abdomen, pelvis, or sacral region. The passage of stool or gas may provide temporary relief of the pain.

Blood in the stool suggests inflammatory, vascular, infectious, or neoplastic disease. The presence of fecal leukocytes indicates mucosal inflammation.

Diarrhea that stops with fasting suggests osmotic diarrhea, except that secretory diarrhea due to fatty acids and bile salt malabsorption may also stop with fasting. Large-volume diarrhea that continues during fasting is most likely secretory. Persistence of diarrhea at night suggests the presence of an organic cause rather than irritable bowel syndrome. Fecal incontinence may be due to anal disease or sphincter dysfunction.

Diet

The correlation of patients’ symptoms with ingestion of milk, other dairy products, or sorbitol-containing artificially sweetened diet drinks, candy, and chewing gum should also be noted.

Physical examination of the patient should focus on the general condition of the patient, degree of hydration, presence of fever, and other systemic origins of toxicity. A variety of physical findings can be sought in a patient with chronic diarrhea and may give clues to the etiology of the diarrheal process. These include goiter, skin rash, arthritis, peripheral neuropathy, postural hypotension, abdominal bruit, perianal abscess, fistula, and rectal mass or impaction.

Diagnostic tests

The initial laboratory evaluation of the patient should include a complete blood count with differential, serum electrolytes, blood urea nitrogen, and creatinine. A chemistry profile and urinalysis may also help to assess the systemic involvement with the diarrheal state.

Examination of the stool is the most important diagnostic test in the evaluation of a patient with acute or chronic diarrhea. A fresh sample of  stool should be examined for the presence of pus (white cells), blood, and bacterial and parasitic organisms. Best yield is obtained if the examination is repeated on three fresh stool samples obtained on three separate days.

Presence of white blood cells

Wright or methylene blue stain of the stool smeared on a glass slide will demonstrate the white cells if they are present. The presence of fecal leukocytes suggests intestinal inflammation as a result of a mucosal invasion with bacteria, parasite, or toxin. Inflammatory bowel disease and ischemic colitis may also result in white blood cells in the stool.

The absence of fecal leukocytes suggests a noninflammatory noninvasive process (e.g., viral infection, giardiasis, drug-related); however, it is never diagnostic because a false-negative result may occur in inflammatory states.

Occult or gross blood in the stool suggests the presence of a colonic neoplasm, an acute ischemic process, radiation enteritis, amebiasis, or severe mucosal inflammation.

Bacterial and parasitic organisms

Fresh stool samples must be examined for the presence of ova and parasites. Organisms that colonize the upper small intestine may not be found in stool samples, and duodenal or jejunal aspirates or biopsies or the string test may be required. Stool cultures will help determine the bacterial pathogen in most cases. However, special techniques may sometimes be necessary, such as for Yersinia, Campylobacter, Neisseria gonorrhoeae, C. difficile, and E. coli: H7.

Fat and phenolphthalein. In the evaluation of chronic or recurrent diarrhea, stool should also be examined for the presence of fat (qualitative and quantitative) and phenolphthalein. Phenolphthalein is found in many laxative preparations and gives a red color when alkali is added to the stool filtrate.

Sigmoidoscopy or colonoscopy or both should be performed without cleansing enemas. Stool samples may be obtained with a suction catheter for microscopic examination and cultures. Most patients with acute or traveler’s diarrhea do not need proctosigmoidoscopic examination. Sigmoidoscopy is especially helpful in the evaluation of:

Bloody diarrhea.

Diarrhea of uncertain etiology.

Inflammatory bowel disease, pseudomembranous colitis, pancreatic disease, or laxative abuse (melanosis coli).

Radiologic studies. Most causes of diarrhea become apparent after the preceding tests. However, in chronic or recurrent diarrhea, barium studies of the large and small intestine may demonstrate the location and extent of the disease. It should be remembered that once barium is introduced into the bowel, examination of the stool for ova and parasites and cultures may be fruitless for several weeks because barium alters the gut ecology.

Other tests

In cases of chronic diarrhea, other specialized tests may be necessary to assess for malabsorption, bacterial overgrowth, or abnormal hormonal states. These are discussed in appropriate chapters.

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