MALABSORPTION

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MALABSORPTION

• M.Prasad Naidu
• MSc Medical Biochemistry,
• Ph.D.Research Scholar

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DEFINITION

• The term malabsorption denotes disorders in which
  there is a disruption of digestion and nutrients
  absorption.
• Impairment can be of single or multiple depending
  on the abnormality.
• This may lead to malnutrition and a variety of
  anaemias.

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PATHOPHYSIOLOGY

• Digestion is by enzymatic hydrolysis which is
  initiated by intraluminal processes requiring
  gastric,pancreatic, and biliary secretions.
• The final products of digestion are absorbed
  through the intestinal epithelial cells.
• Malabsorption constitutes the pathological
  interference with the normal physiological
  sequence of digestion (intraluminal process),
  absorption (mucosal process) and transport
  (postmucosal events) of nutrients.

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• CLASSIFICATION

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• CLINICAL
  FEATURES
• Diarrheoa, often steatorrhoea is the most common
  feature.
• Watery,diurnal and nocturnal,bulky,frequent
  stools are the clinical hallmark of overt
  malabsorption.
• It is due to impaired water, electrolyte
  absorption or irritation from unabsorbed fatty
  acid.
• Bloating, flatulence and abdominal discomfort
  also seen.
• Cramping pain suggests obstructive intestinal
  segment especially if it persist after
  defecation. Eg Crohns disease.

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• Weight loss can be significant despite increased
  oral intake of nutrients.
• Growth retardation,failure to thrive,delayed
  puberty are seen in children.
• Swelling or oedema are seen due to loss of
  protein.
• Anaemias, commonly from vitamin B12, folic acid
  and iron deficiency presenting as fatigue and
  weakness.
• Muscle cramp from decreased vitamin D, calcium
  absorption and they lead to osteomalacia and
  osteoporosis.
• Bleeding tendencies are seen from vitamin K and
  other coagulation factor deficiencies.

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DIAGNOSIS

• As a baseline,the estimation of full blood
  count,ESR,haematinics in the form of
  folate,B12and iron status and serum albumin with
  serum calcium,phosphate and magnesium have to be
  done.
• TESTS FOR FAT MALABSORPTION
• The following methods are available .
• 1.TOTAL FECAL FAT ESTIMATION
• Before the test, the patient is put on a high fat
  diet, consuming between 50-150 g/day of fat for
  three days.
• The patient must collect their feces over the
  next 72 hours using a 1-gallon paint that can be
  well sealed.

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• The fecal sample must be refrigerated to prevent
  any bacterial action.
• Fecal fat analysis is performed by first weighing
  the sample and then extracting the lipids with an
  organic solvent.
• The extraction solvent is evaporated and the dry
  weight of the fat that remains is measured.
• Normal absorption of fat is indicated by a fecal
  fat level of less than or equal to 7 grams per
  day.
• 2.FAT SCREENING
• A more simple but less accurate way to measure
  fat absorption is to count the fat droplets in a
  well mixed sample of the stool specimen using a
  microscope and a neutral fat stain.

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• Another simplified screening test is the fat
  tolerance test called the butterfat or the fatty
  meal test.
• In this test,the patient is asked to fast
  overnight and is given 1 gram of fat per kg of
  body weight.
• Blood is drawn before the dose and again three
  and six hours afterwards.
• The fasting, three-hour and six-hour plasma
  samples are analyzed for triglyceride
  concentration.
• Normal absorption is indicated by at least a 50
  increase in triglycerides over the fasting level.
• The 14C-triolein breath test can be useful to
• make a diagnosis of steatorrhoea in patients
• with difficult diarrhoea.
• It has also been used to monitor pancreatic fat
  malabsorption

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TESTS FOR PANCREATIC MALABSORPTION

• Non-invasive pancreatic function tests include
• 1.The pancreolauryl tests
• It requires the avoidance of Vitamin B and some
  drugs, and two consecutive day 10 hour urine
  collections.
• 2.The PABA test
• It should be reported as a urinary PABA
  excretion index by coadministration of
  p-aminosalicyclic acid or 14C-PABA.
• Both these tests were acceptable as screening
  tests for pancreatic exocrine insufficiency.
• The invasive tests like secretin-cholecystokinin
  test and the Lundh test are in research.

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DISACCHARIDASE MALABSORPTION

• The measurement of disaccharidases, usually
  lactase, maltase and sucrase, is of limited use
  because of high coefficients of Variation.
• They have a role in diagnosing lactase
  deficiency and limited use for monitoring
  disaccharidase deficiencies in coeliac disease.

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HYDROGEN BREATH TEST

• The hydrogen breath test is used to measure two
  things, carbohydrate malabsorption such as
  lactose intolerance and bacterial overgrowth.
• Hydrogen is produced by bacterial fermentation
  of unabsorbed carbohydrates in the intestines.
• The hydrogen produced goes into the blood stream
  and is excreted through the lungs.
• The test is done using a gas chromatograph, an
  apparatus that can separate compounds from one
  another based on their chemical composition.

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• The patient is asked to fast overnight, and his
  or her breath is collected in a plastic syringe
  at the start of the test.
• The patient is then given something to eat
  depending on what is being evaluated.
• The patient's breath will be collected in a
  plastic syringe every thirty minutes for the next
  two to five hours, depending on the test.
• The syringe will be capped and sent to the
  laboratory for analysis.
• The test is simple, non-invasive and not
  diagnostic, it gives the doctor an idea of what
  may be wrong.

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PROTEIN LOOSING ENTEROPATHY

• Chromium radiolabelled albumin or alpha-1
  antitrypsin excretion are the definitive tests.
• BILE ACID MALABSORPTION
• The SeHCAT test with a seven day retention is
  useful but, if unavailable, a simple assessment
  of the clinical response of diarrhoea to
  cholestyramine 4-8gms t.d.s. can be used.

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TESTS FOR CELIAC DISEASE

• Tests for this disease involve drawing the
  patient's blood and testing for the presence of
  three antibodies, antigliadin, antiendomysium,
  and antireticulin antibodies.

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D-XYLOSE ABSORPTION TEST

• D-xylose is a pentose sugar that is not normally
  found in the blood.
• It can be easily absorbed by healthy intestinal
  cells without the aid of pancreatic enzymes, and
  is poorly metabolized so that at least 50 of the
  dose is excreted in the urine within 24 hours.
• This test is a good general screen for
  malfunction of absorption, and helps to
  differentiate intestinal malabsorption syndromes
  (reduced Dxylose absorption) from pancreatitis
  (normal D-xylose absorption).

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• Adults are given an oral dose usually 25 grams of
  D-xylose.
• A five-hour timed urine sample is collected, and
  a blood sample is collected two hours after the
  dose is given.
• Children are given a 5 gram dose of Dxylose, and
  a blood sample is collected one hour after the
  dose is given.

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• Adults should excrete at least 25 of the dose in
  the five-hour urine sample, and have a two-hour
  blood level of at least 25 mg/dL.
• Children should have a one-hour blood level of at
  least 20 mg/dL.
• The D-xylose test will be normal if the patient
  has normal absorptive capacity in the intestine,
  or if the patient has malabsorption that is
  caused by a pancreatic problem.
• It will be low if the patient has celiac
  disease, tropical sprue, Crohn's disease,
  advanced AIDs, or pellegra (niacin deficiency).

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TESTS FOR VITAMIN B12 DEFICIENCY

• It is measured by Schilling test.it has 4 stages.
• Stage 1 oral vitamin B12 plus intramuscular
  vitamin B12
• In the first part of the test, the patient is
  given radiolabeled vitamin B12 to drink or eat.
•  An intramuscular injection of unlabeled vitamin
  B12 is given at or around the same time.
• .

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• The purpose of the single injection is to
  temporarily saturate B12 receptors in the liver
  with enough normal vitamin B12 to prevent
  radioactive vitamin B12 binding in body tissues
  (especially in the liver), so that if absorbed
  from the G.I. tract, it will pass into the urine.
  
• The patient's urine is then collected over the
  next 24 hours to assess the absorption.
• In patients with pernicious anemia or with
  deficiency due to impaired absorption, less than
  5 of the radiolabeled vitamin B12 is detected.

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• Stage 2 vitamin B12 and intrinsic factor
• If an abnormality is found, the test is repeated,
  this time with additional oral intrinsic factor.
• If this second urine collection is normal, this
  shows a lack of intrinsic factor production, or
  pernicious anemia.
• Stage 3 vitamin B12 and antibiotics
• This stage is useful for identifying patients
  with bacterial overgrowth syndrome.
• Stage 4 vitamin B12 and pancreatic enzymes
• This stage, in which pancreatic enzymes  are
  administered, can be useful in identifying
  patients with pancreatitis.

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• Stage 3 vitamin B12 and antibiotics
• This stage is useful for identifying patients
  with bacterial overgrowth syndrome.
• Stage 4 vitamin B12 and pancreatic enzymes
• This stage, in which pancreatic enzymes are
  administered, can be useful in identifying
  patients with pancreatitis.

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BIOPSY OF SMALL INTESTINAL MUCOSA

• It is useful to confirm the diagnosis.

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MALABSORPTION TREATMENT

• Management includes
• (1) the correction of nutritional deficiencies,
  and
• (2) when possible, the treatment of causative
  diseases.
• Nutritional support
• Supplementing various minerals, such as calcium,
  magnesium, iron, and vitamins, which may be
  deficient in malabsorption, is important.
• Caloric and protein replacement also is
  essential.
• Medium-chain triglycerides can be used as fat
  substitutes because they do not require micelle
  formation for absorption and their route of
  transport is portal rather than lymphatic.
• In severe intestinal disease, such as massive
  resection and extensive regional enteritis,
  parenteral nutrition may become necessary.

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• Treatment of causative diseases
• A gluten-free diet helps treat celiac disease.
• Similarly, a lactose-free diet helps correct
  lactose intolerance supplementing the first bite
  of milk-containing food products with Lactaid
  also helps.
• Protease and lipase supplements are the therapy
  for pancreatic insufficiency.
• Antibiotics are the therapy for bacterial
  overgrowth.
• Corticosteroids, anti-inflammatory agents, such
  as mesalamine, and other therapies are used to
  treat regional enteritis.

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