Stool Acidity Test
Medical Author:
Jay W. Marks, M.D.
Medical Editor: William C. Shiel,
Jr., MD, FACP, FACR
What is a stool acidity test?
The stool acidity test is a test for diagnosing intolerance to lactose, the
sugar contained in milk, in infants and very young children.
What is lactose intolerance?
Lactose intolerance is the inability to digest the
lactose sugar in milk. Milk containing the sugar lactose is a main source of
nutrition for infants and
young children. With normal lactose tolerance, all of the lactose is digested
(broken down into two smaller sugars) and absorbed in the small intestine so
that none reaches the colon.
On the other hand, in individuals with lactose
intolerance who lack the intestinal enzyme that breaks down the lactose, the
ingested lactose is neither digested nor absorbed in the small intestine and
reaches the colon where it is used by the bacteria in the colon.
The bacteria produce chemicals that cause diarrhea and also produce
gas. Some of
the chemicals produced by bacteria include lactic and other acids that turn the
stool acidic.
Individuals with intolerance to lactose cannot drink regular cow's
milk without developing diarrhea, gas, and often abdominal pain. They instead
must drink substitutes like rice or soy milk or treat cow's milk with an enzyme
that digests the lactose (Lactaid) so that the smaller sugars can be absorbed in
the small intestine.
How does the stool acidity test work?
During the stool acidity test, infants and very young
children are given lactose to drink. With normal tolerance to lactose, all of
the lactose is digested and absorbed in the small intestine. In individuals who
are lactose intolerant, some or all of the lactose is not digested and absorbed
in the small intestine and reaches the colon. Through the action of the colonic
bacteria, the
stool becomes acid. The acidity of stools that are passed after ingestion of the
lactose then is measured. If the stool becomes acid, the individual is
intolerant of lactose.
Next: How does testing for lactose intolerance differ in adults? »
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