1. The patient should not have eaten slowly digesting foods like beans, bran or other high fiber cereals the day before the test is performed.
2. The patient should fast for 12 hours, with no food and only water to drink before the test.
3. The patient should not smoke, sleep, or exercise vigorously for at least ? hour before, or at any time during the test.
4. Ask the patient about any recent antibiotic therapy and/or recent or current diarrhea. Make the physician aware of such conditions if they have occurred, since they can affect the test.
If the patient meets the pre-conditions for testing as outlined above, proceed with the following protocol
1. Collect an alveolar sample and analyze it to establish a baseline for breath H2. The H2 baseline is typically less than 10 parts per million (ppm). Higher values for H2 may indicate incomplete fasting prior to the test, the ingestion of slowly digesting foods the day before, or (if the level exceeds 20-30 ppm) the presence of bacterial overgrowth in the small intestine.
2. Prepare the challenge dose of sugar. Ordinarily, 1 gm per kg body weight of the patient is dissolved in 6-8 oz. water. Some physicians use 2 gm/kg for lactose malabsorption, but little increase in reliability is seen with the larger dose. Other sugars require a slightly different dose for the standard test. A smaller dose of 0.25-0.50 gm/kg body weight is standard for sorbitol or to establish the presence of congenital glucose malabsorption. For the standard sugar dose, at least 6-8 oz of water should be used for the solution, to be sure the volume is large enough to stimulate emptying of the stomach when the solution is ingested. A proportionately larger volume of water should be used with neonates, to provide greater dilution of the sugar, because a higher concentration of sugar in the intestines may cause an osmotic shift of water, resulting in a reaction similar to the "dumping syndrome". Heating the water to make the sugar dissolve more easily is a standard part of most test procedures. Disaccharides are not easily dissolved in cold water but are readily dissolved in warm or hot water. Cool the solution in a refrigerator before giving it to the patient.
3. Have the patient ingest the designated dose of the sugar. It is common to use 1.0 gm/kg body weight up to 25 gm. Higher doses are used by some physicians to demonstrate symptoms for patients who are malabsorbers, but most literature suggests that 1 gm/kg produces reliable test results without causing uncomfortable cramping, bloating and diarrhea in lactose intolerant patients.
4. For the standard protocol, an alveolar sample is collected and analyzed every 30 minutes beginning 1 hour after the ingestion of the lactose until the H2 in the alveolar air exceeds the baseline or the lowest value by at least 20 ppm, or for up to 3 hours if the challenge dose was lactose sugar dissolved in water. IF milk is used as the challenge dose, an additional hour should be added to allow for a possibly longer transit time caused by slower gastric emptying. IF food is consumed, the test period should be prolonged to 5-6 hours.
These guidelines should be used along with the patient history, clinical judgment and other considerations available to the physician. The concentrations refer to the "corrected values" if the CO2 correction factor has been applied to the analysis.
The H2 concentration in an alveolar air sample from a healthy patient who has fasted for 12 hours is normally less than 10 ppm (parts per million). With patients who have elevated control values (e.g., 10-20 ppm) due to residual fiber in the colon, the H22 level might fall during the test period as the colon fiber-content is reduced through digestion. If the patient is a lactose malabsorber, the change in trace-gas levels should be related to the lowest point recorded for the H2 level prior to its increase.
If the patient is a lactose malabsorber, the breath H2 concentration will increase by over 20 ppm within the test period following the ingestion of 1 gm lactose per kg body weight. The positive response results from undigested lactose reaching the colon where bacteria hydrolyze the sugar and produce H2 as a metabolic product. The gas is equilibrated with the blood perfusing the colon and is returned to the lungs, where it is lost in the exhaled air. In lactose absorbers, the lactose is hydrolyzed to glucose and galactose by lactase enzyme and they are absorbed in the small intestine. Thus, there is normally no significant change in the breath H2 during the test, but some variation (of a few ppm) in alveolar concentrations is common.
In general, lactose malabsorbers who have the greatest rise in breath H2 following the challenge dose of lactose will have more severe lactose intolerance (more severe symptoms or greater sensitivity to milk products).
An increase of 20-40 ppm in the H2 response during the test would generally be classified as a mild response. If the increase reached 40-80 ppm, it would be considered moderate, and if it increased by more than 80 ppm it would generally be classified as a severe degree of lactose malabsorption.
Such a guideline is only semi-quantitative because the proportion of intestinal gases which are absorbed into the blood stream can be quite variable (some of the early reports not withstanding), and the perception of symptom severity is at least partly subjective. When the increases in breath H2 are mild or moderate, advising the patient to limit the intake of milk products and avoid large amounts of the offending lactose at any one meal may be sufficient to prevent symptoms of lactose intolerance. Use of the commercially available lactase enzyme preparations may provide relief if the restrictions are exceeded. It has been demonstrated that milk is tolerated better by lactose malabsorbers if its ingestion is accompanied by food, rather than consumed alone. When the increase lactase enzyme preparations is virtually mandatory when milk products are consumed.