MALABSORPTION

M.Prasad NaiduMSc Medical Biochemistry,

Ph.D.Research Scholar

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.

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.

CLASSIFICATION

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; Crohn’s disease.

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.

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.

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.

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

TESTS FOR PANCREATIC MALABSORPTIONNon-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.

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.

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.

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.

PROTEIN LOOSING ENTEROPATHYChromium 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.

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.

D-XYLOSE ABSORPTION TESTD-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).

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.

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).

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.

Stage 2: vitamin B12 and intrinsic factorIf 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 antibioticsThis stage is useful for identifying patients with

bacterial overgrowth syndrome.

Stage 4: vitamin B12 and pancreatic enzymesThis stage, in which pancreatic enzymes  are

administered, can be useful in identifying patients with pancreatitis.

BIOPSY OF SMALL INTESTINAL MUCOSA:It is useful to confirm the diagnosis.

MALABSORPTION TREATMENTManagement 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.

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.