Lactose Intolerance (cont.)
Siamak T. Nabili, MD, MPH
Siamak T. Nabili, MD, MPH
Dr. Nabili received his undergraduate degree from the University of California, San Diego (UCSD), majoring in chemistry and biochemistry. He then completed his graduate degree at the University of California, Los Angeles (UCLA). His graduate training included a specialized fellowship in public health where his research focused on environmental health and health-care delivery and management.
Bhupinder Anand, MD
IN THIS ARTICLE
Exams and Tests
Evaluation of lactose intolerance includes a careful medical history, review of symptoms, and physical examination.
Because symptoms are usually non-specific, other potential diagnosis also needs to be considered and excluded. These include:
Some of the commonly recommended methods for the evaluation of lactose intolerance will be discussed this section.
Elimination of dietary lactose is a subjective self-test commonly done by many people who think they may have lactose intolerance. This easy test is a self evaluation to assess if symptoms resolve with avoidance of dietary lactose. The limitation of this test is that lactose may exist in many foods other than milk and milk products. Complete restriction of lactose products, therefore, is difficult. Consultation with a dietician or nutritionist may help to identify other lactose containing, non-milk foods. Another limitation of the self-test is a possible placebo effect where people may think their symptoms are better, when in fact they are not.
Milk Tolerance Test
The milk tolerance test is a simple and relatively reliable test that can be performed to evaluate lactose intolerance. In this test, a person drinks a glass of milk in the morning after an overnight fast and then resumes fasting for the next 3-5 hours. If the typical symptoms of lactose intolerance occur within a few hours after the intake of milk, the person is likely to have lactose intolerance. If symptoms do not occur, lactose intolerance is unlikely. It is recommended that nonfat milk be used for this test to eliminate the possibility of symptoms resulting from fat intolerance.
Milk allergy is an uncommon condition that can present in a similar manner, although this condition typically occurs almost always in infants and young children.
Lactose Tolerance Test
The lactose tolerance test is a more objective evaluation in assessing individuals with symptoms suggestive of lactose intolerance. This test involves an overnight fast and measurement of a fasting baseline blood glucose level in the morning. Then, 50 grams of lactose is ingested and blood glucose measurements are taken 60 minutes and 120 minutes later. The diagnosis of lactose intolerance is made if there is a less than 20 grams/deciliter (one tenth of a gram) increase in the blood glucose level from baseline. If the glucose level increases by more than 20 grams/deciliter, it means that lactase activity in the intestines is sufficient to split lactose into glucose and galactose. This test is very specific, but not very sensitive, meaning a normal test does not exclude lactose intolerance. The presence of diabetes mellitus and bacterial overgrowth in the intestines can give normal results despite actual lactase deficiency. Additionally, abnormal emptying of food from the stomach (either too rapid or too slow) can cause abnormal test results.
Hydrogen Breath Test
The hydrogen breath test is the most reliable test and the method of choice for the assessment of lactose intolerance. This test takes advantage of hydrogen production by the bacteria in the colon when these bacteria metabolize lactose and produce hydrogen gas. Some of the gas is excreted as flatus and some is absorbed by the body where it is eventually exhaled through the lungs. The amount of exhaled hydrogen gas is measured. After an overnight fast, 25 grams of lactose (about 16 ounces of milk) are ingested. Hydrogen gas in the breath is measured before the ingestion, as a baseline value, and then every 30 minutes for three hours. An increase in breath hydrogen concentration of more than 20 parts per million from baseline is diagnostic of lactose intolerance and lactase deficiency. The amount of expired hydrogen gas can also help determine the severity of lactase deficiency. The hydrogen breath test also has its shortcomings. The results can be abnormal because of bacterial overgrowth in the intestines. It is also a long and tedious test.
Stool Acidity Test
The stool acidity test is sometimes performed in infants and young children suspected of having lactose intolerance. When lactose is split by bacteria in the colon, some acid (lactic acid) is produced as a result of the chemical reaction by the bacteria. In this test, the infant is given small amounts of lactose and stool samples are collected for measurement of acidity. Stool that is more acidic than normal may suggest lactase deficiency. This test is infrequently done due to its inferiority to the hydrogen breath test.
Biopsy of the Small Intestine
Biopsy of the small intestine is an invasive test that is rarely done for the evaluation of lactose intolerance. The biopsy is usually performed by endoscopy where a long tube is passed from the mouth and into the small intestine. Biopsies of the lining of the intestinal wall are taken and analyzed for lactase activity. This test is not available routinely except for research purposes in specialized centers. The results may also not be as reliable because the biopsied area of the intestine may have normal lactase activity compared to other areas of lactase deficiency that may be missed by the biopsy.
Imaging studies, such as X-rays and CT scans, are not generally recommended in the evaluation of lactose intolerance, although these studies may be helpful in eliminating other possible diagnoses.
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