Lactose Intolerance (cont.)
Blood glucose test
The blood glucose test is an older test for lactase deficiency and lactose
intolerance. For the blood glucose test, lactose is ingested (usually 0.75 to
1.5 gm of lactose per kg of body weight) after an overnight fast, and serial
blood samples are drawn and analyzed for glucose. If the level of blood glucose
rises more than 25 mg/100ml, it means that the lactose has been split in the
intestine and the resulting glucose has been absorbed into the blood. This
implies that lactase levels are normal. Unfortunately, the blood glucose test,
though simple in principle, requires the collection of multiple samples of
blood. Moreover, the test has many real and potential problems, the most common
of which is false positive tests, that is, an abnormal test in people who have
normal lactase levels and no lactose intolerance. For these reasons, the blood
glucose test is not often used.
Stool acidity test
The
stool acidity test is a test for lactase deficiency in
infants and young children. For the stool acidity test, the infant or child is given a small
amount of lactose orally. Several consecutive stool samples then are tested for
acidity. With a deficiency of lactase, unabsorbed lactose enters the colon and
is split into glucose and galactose. Some of the glucose and galactose is broken
down by the bacteria into acids, for example, lactic acid. Lactic acid turns the
stool acidic. Therefore, a lactase deficient infant or child will develop an
acidic stool following the test dose of lactose.
Despite the availability of the stool acidity test, the superiority of breath
testing has led to modifications in equipment for collecting breath samples that
makes it easier to do breath testing in young children and even infants. As a
result, the stool acidity test is not done frequently.
Intestinal biopsy
The most direct test for lactase deficiency is biopsy of the intestinal
lining with measurement of lactase levels in the lining. The biopsy can be
obtained by endoscopy or by
special capsules that are passed through the mouth or nose and into the small
intestine. The analysis of lactase levels in the
biopsy requires specialized procedures that are not often available, and, as a
result, lactase levels are not often measured except for research purposes.
Next: Intestinal biopsy »
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