Malabsorption Workup

Updated: Jan 24, 2019
  • Author: Muhammad Bader Hammami, MD; Chief Editor: Praveen K Roy, MD, AGAF  more...
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Workup

Laboratory Studies

The choice and order of diagnostic testing should be individualized and guided by the patient’s history and physical examination.

Hematologic tests indicated in the workup of malabsorption include the following:

  • A complete blood cell (CBC) count may reveal microcytic anemia due to iron deficiency or macrocytic anemia due to vitamin B12 (cobalamin) or B9 (folate) malabsorption.

  • Serum iron, vitamin B12, and folate concentrations may help establish a diagnosis.

  • Prothrombin time may be prolonged because of malabsorption of vitamin K, a fat-soluble vitamin.

Levels of electrolytes and studies of serum chemistries may be indicated in the workup of malabsorption. Note the following:

  • Malabsorption can involve electrolyte imbalances, such as hypokalemia, hypocalcemia, hypomagnesemia, and metabolic acidosis.

  • Protein malabsorption may cause hypoproteinemia and hypoalbuminemia.

  • Fat malabsorption can lead to low serum levels of triglycerides, cholesterol, and alpha- and beta-carotene.

  • Westergren sedimentation rate is elevated in Crohn disease and Whipple disease.

No serologic tests are specific for malabsorption. Note the following:

  • Serum antigliadin and antiendomysial antibodies can be used to help diagnose celiac sprue.

  • Serum immunoglobulin A (IgA) can be used to rule out IgA deficiency.

  • Determination of fecal elastase and chymotrypsin (two proteases produced by the pancreas) levels can be used to try to distinguish between pancreatic causes and intestinal causes of malabsorption.

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Imaging Studies

Small bowel barium studies may reveal the following findings:

  • An abnormal small bowel pattern obtained from barium studies of the upper gastrointestinal tract may reveal the nature of malabsorption.

  • The mucosa pattern associated with celiac disease often becomes obliterated or coarsened.

  • Flocculation of the barium occurs in the gut lumen.

  • Small bowel dilatation and diverticulosis are frequently identified in scleroderma.

  • Regional enteritis of the small intestine can lead to stricture, ulceration, and fistula formation.

  • Other anatomic abnormalities, such as surgical changes or enterocolonic fistula, also can be detected on radiographs.

A computed tomography (CT) scan of the abdomen may help detect evidence of chronic pancreatitis, such as pancreatic calcification or atrophy. Enlarged lymph nodes are seen in Whipple disease and lymphoma.

CT enterography and magnetic resonance (MR) enterography are used to detect small bowel mucosal disease and neoplasms.

A plain abdominal radiograph may reveal pancreatic calcifications indicative of chronic pancreatitis.

Magnetic resonance cholangiopancreatography (MRCP) or endoscopic ultrasound (EUS) can help detect the cause of malabsorption due to pancreatic disease such as chronic pancreatitis or pancreatic malignancy.

Wireless capsule endoscopy allows for visualization of the entire small bowel and evaluation of small bowel mucosal disease.

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Other Tests

Fat malabsorption studies

Fat malabsorption is usually the first test obtained because many disease processes result in fat malabsorption. Instruct patients to consume a normal amount (80-100 g/d) of fat before and during the collection. Based on this intake, fecal fat excretion in healthy individuals should be less than 7 g/d.

For a quantitative measurement of fat absorption, a 72-hour fecal fat collection is often performed and is considered the criterion standard. Raman et al have suggested that a novel clinical test that uses levels of serum retinyl palmitate to identify severe cases of fat malabsorption may be useful relative to the 72-hour fecal fat test. [11]

Qualitative tests include the acid steatocrit test and Sudan III staining of stool, but these tests are less reliable.

D-xylose test

If the 72-hour fecal fat collection results demonstrate fat malabsorption, the D-xylose test is used to document the integrity of the intestinal mucosa.

Facilitated diffusion in the proximal intestine primarily absorbs D-xylose. Approximately half of the absorbed D-xylose is excreted in urine, unmetabolized. If the absorption of D-xylose is impaired due to either a luminal factor (eg, bacterial overgrowth) or a reduced or damaged mucosal surface area (eg, surgical resection, celiac disease), urinary excretion is lower than normal.

Cases of pancreatic insufficiency usually result in normal urinary excretion because the absorption of D-xylose remains intact.

Carbohydrate absorption studies

A simple sensitive test for carbohydrate malabsorption is the hydrogen breath test, in which patients are given an oral solution of lactose. [12, 13]  In cases of lactase deficiency, colonic flora digest the unabsorbed lactose, resulting in an elevated hydrogen content in the expired air. Bacterial overgrowth or rapid transit also can cause an early rise in breath hydrogen, necessitating the use of glucose instead of lactose to make a diagnosis. However, 18% of patients are hydrogen nonexcretors, causing a false-negative test result.

Bile salt absorption studies

The bile salt breath test can determine the integrity of bile salt metabolism. The patient is given oral conjugated bile salt, such as glycine cholic acid with the glycine radiolabeled in the carbon position. The bile salt is deconjugated and subsequently metabolized by bacteria, leading to a radioactively labeled elevated breath carbon dioxide level in the presence of interrupted enterohepatic circulation, such as bacterial overgrowth, ileal resection, or disease.

Schilling test

Malabsorption of vitamin B12 (cobalamin) may occur as a consequence of a deficiency of intrinsic factor (eg, pernicious anemia, gastric resection), pancreatic insufficiency, bacterial overgrowth, ileal resection, or disease. The three-stage Schilling test results often can help differentiate these conditions.

13C-D-xylose breath test

Hope et al suggested that small intestinal malabsorption in chronic alcoholism may be determined by a 13C-D-xylose breath test. [14] The investigators evaluated the 13C-D-xylose breath test in 14 alcoholics, compared the breath test results with those of untreated celiac patients and healthy controls, and correlated the breath test findings to morphologic findings of the duodenal mucosa. [14] Their findings showed significantly reduced absorption of 13C-D-xylose in the alcoholic individuals relative to the healthy controls, whereas the time curve of 13C-D-xylose absorption in the alcoholics was similar in appearance to that of the untreated celiac patients. In addition, despite few light microscopic changes in the alcoholic individuals, morphologic pathology, primarily a reduced surface area of microvilli, was observed under electron microscopy in the majority of the patients. [14]

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Procedures

Upper endoscopy with small bowel mucosal biopsy

Establishing a definitive diagnosis of malabsorption of the mucosal phase often can be achieved by histologic examination of biopsied mucosal specimens obtained during routine upper endoscopy.

Examples of conditions that can be diagnosed this way include celiac sprue, giardiasis, Crohn disease, Whipple disease, amyloidosis, abetalipoproteinemia, and lymphoma.

Magnification narrow band imaging with upper endoscopy for the evaluation of duodenal villi may be predictive for the presence of villous atrophy or normal villi, which could be helpful for targeted biopsies. [15] In a prospective study, 16 of 100 patients who underwent upper endoscopy with magnification narrow band imaging for suspected malabsorption had histologically confirmed villous atrophy. Two endoscopists independently demonstrated this technique had a greater than 80% sensitivity (87.5% vs 81.3%) and a more than 92% specificity (95.2% vs 92.9%) for detecting villous atrophy; the interobserver agreement was very good (kappa = 0.87). [15]

Colonoscopy 

Colonoscopy with intubation of the terminal ileum may be useful in the evaluation of ileal Crohn disease.

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Histologic Findings

Depending on the cause, the histologic features of malabsorption vary. A frequently encountered histologic finding is villous atrophy, which is seen in celiac disease, tropical sprue, viral gastroenteritis, bacterial overgrowth, inflammatory bowel disease, immunodeficiency syndromes, lymphoma, and radiation enteritis.

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