the diagnosis of lactose intolerance

Discussion in 'MRCS Forum' started by Lona., Nov 17, 2007.

  1. Lona.

    Lona. Guest

    Each of the following studies s helpful in the diagnosis of lactose intolerance EXCEPT-
    a- Rectum of symptoms with lactose challenge
    b- Hydrogen excretion in breath after oral admission of lactose
    c- Biopsy of the small intestine and enzyme (lactose) assay
    d- Stool pH and reducing substances
    e- pH probe of the esophagus
  2. Lona.

    Lona. Guest

    Answer: - The answer is E. (Rudolph 20/e, pp 1083-1085.) Measurement of esophageal pH is useful in the diagnosis of gastroesophageal reflux. Lactose is a disaccharidase localized in the brush border of the intestinal villous cells. It hydrolyzes lactose to its constituent monosaccharides, glucose and galactose. Intestinal lactose levels are usually normal at birth in al populations; however, lactose deficiency is a common, genetically predetermined condition. Sucrose, also a disaccharide, is a nonreducing sugar composed of glucose and fructose that is hydrolyzed by the brush border enzyme sucrose. Lactose activity is not readily increased by the oral administration of substrate or the inclusion of lactose in the diet. The clinical symptoms of lactose mal-absorption are due to the presence of osmotically active, undigested lactose, which may act to increase intestinal fluid volume, alter transit time, and produce the symptoms of abdominal cramps, distention, and occasionally, watery diarrhea. Bacterial metabolism of the nonabsorbed carbohydrates in the colon to carbon dioxide and hydrogen may contribute to the clinical symptoms. Acquired lactose deficiency is often associated with conditions of the gastrointestinal tract that cause intestinal mucosal injury (e.g. sprue and regional enteritis)
    Diagnostic techniques for lactose intolerance include removal of the offending sugar with a reproduction of symptoms. Although the ingestion of even small amounts of lactose can be diagnostic if gastrointestinal symptoms occur, the measurement of breath hydrogen is more specific as it is not affected by glucose metabolism or gastric emptying. Similarly, an acidic stool pH in the presence of reducing substances would be diagnostic. Direct measurement of enzyme levels combined with histologic evaluation helps to differentiate an acquired (secondary versus primary) lactose deficiency in which the intestinal histology is normal.

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