Malabsorption Syndrome

Malabsorption is a general term used to describe a number of clinical conditions in which one or more important nutrients are inadequately absorbed by the gastrointestinal tract with increased fecal content of intestinal nutrients or their bacterial degradation products.

Malabsorption results from defect in:

1. Intraluminal digestion in which protein, carbohydrate and fats are broken down by secreted enzymes.
2. Terminal digestion by enzymes of enterocyte membrane (disaccharidases & peptidases). Involves hydrolysis of carbohydrates and peptides.
3. Transepithelial transport of nutrients, fluid, and electrolytes, through enterocytes.

1. Defective intraluminal digestion:
-Pancreatic dysfunction;
Pancreatic insufficiency- (pancreatitis or cystic fibrosis)
Inactivation of pancreatic enzymes by excess gastric acid secretion -(Zollinger Ellison syndrome).
-Deficient or ineffective bile salts;
Decreased bile salt uptake -( ileal resection or dysfunction).
Impaired excretion of bile - ( liver disease)
Bacterial overgrowth - Occurs: (i) due to disturbance of motility (blind intestinal loop, multiple strictures, jejunal diverticula, fistulas). (ii) Hypochlorhydria or achlorhydria (iii) immune deficiencies or impaired mucosal immunity.
Muscular or neurogenic defect of intestinal wall causing distrubance of motility (amyloidosis, scleroderma, diabetic enteropathy).

2. Primary mucosal cell abnormalities:
- Disaccharidase deficiency- Disaccharidases (most important is lactase) are essential for sugar absorption. Disaccharidases are bound to the microvillous membrane. Abnormal function of microvilli may be primary (primary disaccharidase deficiency) or secondary (damage to villi due to celiac disease).
- Bacterial overgrowth with brush border damage
- Abetalipoproteinemia- Absorptive cells are unable to synthesize apoprotein B required for assembly of lipoproteins and chylomicrons.
- Vitamin B12 malabsorption- Parietal cell loss (pernicious anemia), ileal dysfunction or resection.

3. Reduced small intestinal surface area:
Gluten sensative enteropathy (celiac disease) ; Short gut syndrome
Crohn's disease ; Lympoma associated diffuse enteritis ;
Allergic and eosinophilic gastroenteritis.

4.Infection
Whipple's disease ; Parasitic infestation ; Acute infectious enteritis
Tropical sprue ; Bacterial overgrowth

5. Lymphatic obstruction
Lymphoma ; Tuberculosis & tuberculous lymphadenitis ; Intestinal Lymphangiectasia.

6. Iatrogenic
Gastrectomy ; Distal ileal resection or bypass ; Radiation

7. Drug- induced
Laxative ; Neomycin ; Cholestyramine

8. Miscellaneous
Diabetes ; Hypo & hyperthyroidism ; Mastocytosis ; Amyloidosis ; Carcinoid syndrome ; Hypogammaglobulinemia

LABORATORY INVESTIGATIONS IN MALABSORPTION SYNDROME:

ROUTINE TEST

1. Hemogram- Microcytic anemia- Iron
Macrocytic anemia- Vit B12 , folate
2. Prothrombin time- Vit K level decreased
3. Serum albumin- Decreased (protein loss)
4. Hypocalcemia, hypophosphatemia, increased alkaline phosphatase - Vit D malabsorption
5. Stool examination for fat, ova or cysts.

SPECIAL TESTS

A. Fat absorption:

1.Fecal fat microscopy-
(Sudan III black ) Normal - Less than 100 globules
2. Quantitative fecal fat analysis:
(one of the best tests for fat absorption).
Normal- 3-5 gm fat / day excreted. More than 6gm/day is significant.
3. Serum Carotene level falls in fat malabsorption.
4. Serum cholesterol- decreased in malabsortion
5. Radioisotope labelled fat breath tests.

B. Carbohydrate absorption :

1. D-xylose absorption test: Monosaccharide absorbed in jejunum. Decreased level seen in:
i) jejunal mucosal disease ii) bacterial overgrowth syndrome (breakdown of xylose).
2. Glucose tolerance test- flat curve
3. Lactose tolerance test- Intolerance in infants due to lactase deficiency or in adults with lactase deficiency .
Eg: Celiac, tropical sprue etc.
4. Hydrogen breath test- (Disaccharidase deficiency and bacterial overgrowth ). Increased H2 in breath if disaccharidase level is low due to increased sugar in the gut.

C. Protein absorption:

1. Fecal microscopy- Animal skeletal muscle fibre
2. Fecal nitrogen - Normal- 2-2.5 gm/day .
Azotorrhoea- More than 3gm/day
3. Protein losing enteropathy
Increased fecal clearance of alpha-1-antitrypsin. There is increased protein leakage in the intestine.
4. Serum albumin is decreased.

D. Vitamin absorption:

1. Vitamin B12- Schilling test
2. Serum folate- Indicator of jejunal dysfunction
3. Prothrombin time- Vit K decreased

E. Bile salt reabsorption:

Bile acid breath test: Labelled glycine is used.
Bile acid glycocholate is formed.
In ileal dysfunction, jejunal bacterial overgrowth, short bowel syndrome, there is labelled bile acid breakdown in colon.

F. Mineral absorption:

Serum calcium, phosphorus, magnesium. Iron and TIBC.

PANCREATIC FUNCTION TESTS
Secretin test- Duodenal contents are assayed for enzymes.
Lundh test- Duodenal juice analysed for trypsin activity.

OTHER MISCELLANEOUS TESTS
Duodenal aspirate: (microscopy- Giardia, culture- bacterial overgrowth.
Immunoglobulins: Agammaglobulinemia
Lipoproteins: Abetalipoproteinemia