These will help determine whether patients have anemia, low protein levels, and deficiencies of certain vitamins and minerals. Blood tests can also be used to make specific diagnoses.
X-rays of the abdomen can help to make certain diagnoses such as distended loops of bowel which may be seen in bowel obstruction or problems with gas formation. Barium enema and barium meal studies are also useful to determine the anatomical features of the intestine and particularly to look for abnormalities.
Multiple stool studies can be performed to evaluate any patient with malabsorption particularly when it manifests as diarrhea. The patient is asked to ingest at least 80gm of fat per day, and stools are collected for 1–3 days. The total amount of fat excreted in the stool is determined in the laboratory. This is helpful in determining the degree of malabsorption; usually less than 7gm of fat per day are excreted in stool. Bile acid deficiency and bacterial overgrowth usually do not produce a fecal fat of more than 30gm per day. Patients with celiac disease will rarely produce more than 60gm of fat per day in the stool. Severe steatorrhea (80–100 gm of fat per day) is seen in patients with pancreatic insufficiency or in patients who have had significant bowel resected.
Xylose absorption test
This is a very useful test to evaluate the integrity of the intestinal mucosa and its ability to absorb. D-xylose is a sugar that is absorbed across the intestinal mucosa and can be measured in the urine and blood. After a patient drinks the Xylose, urine or blood are collected over the next several hours. Low Xylose levels in the blood or urine are highly suggestive of an abnormality of the intestinal mucosa.
Pancreatic function tests
A tube is placed through the nose or mouth so that its tip is lying next to the opening of the pancreatic duct into the duodenum. Secretions are collected and the content of bicarbonate and enzymes are measured after the pancreas has been stimulated with a hormone called secretin or with a test meal. Pancreatic insufficiency is indicated if the bicarbonate and enzyme concentrations are very low.
Another pancreatic function test, the Bentiromide test, involves ingestion of a chemical called bentiromide. This is broken down by pancreatic enzymes and one constituent (paraaminobenzoicacid, PABA) is absorbed and excreted in the urine. Pancreatic insufficiency is suspected when urinary PABA levels are low.