Lactose intolerance (or hypolactasia) is a common cause

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1 ORIGINAL ARTICLE A Comparison Between Lactose Breath Test Quick Test on Duodenal Biopsies for Diagnosing Lactase Deficiency in Patients With Self-reported Lactose Intolerance Manuele Furnari, MD,* Daria Bonfanti, MD,* Andrea Parodi, MD, PhD,* Jola Franze`, MD,w Edoardo Savarino, MD, PhD,* Luca Bruzzone, MD,* Alessro Moscatelli, MD,* Francesco Di Mario, MD,w Pietro Dulbecco, MD,* Vincenzo Savarino, MD* Background: A lactose breath test (LBT) is usually used to diagnose lactase deficiency, a lactose quick test (LQT) has been proposed as a new test on duodenal biopsies to detect this disorder. Goals: We aimed to assess the diagnostic accuracy of LBT LQT their ability to predict the clinical response to a lactosefree diet in patients with self-reported lactose intolerance. Study: Fifty-five patients (age 47 ± 14 y; M/F 15/36) underwent upper gastrointestinal endoscopy 25g-LBT. Two duodenal biopsies were taken to determine lactase deficiency (normal, mild, or severe) by LQT to rule out other causes of secondary lactose malabsorption. Patients with a positive LBT normal LQT also underwent a glucose breath test to exclude small intestinal bacterial overgrowth as a cause of the former result. The severity of gastrointestinal symptoms was measured with a GSS questionnaire, under basal condition 1 month after a lactose-free diet. Results: Lactose malabsorption was detected in 31/51 patients with LBT in 37/51 patients with LQT (P = NS). Celiac disease was found in 2 patients. Two LBT + patients showed a positive glucose breath test for small intestinal bacterial overgrowth. Eight patients had a mild hypolactasia by LQT a negative LBT, but they had a significant improvement of symptoms after diet. LQT LBT were concordant in 83% of cases predicted the response to a lactose-free diet in 98% 81% of the cases, respectively (P = 0.03). Conclusions: LQT is as sensitive as LBT in detecting lactase deficiency; however, it seems to be more accurate than LBT in predicting the clinical response to a lactose-free diet. Key Words: lactose intolerance, malabsorption, lactose breath test, lactose quick test, diet (J Clin Gastroenterol 2013;47: ) Received for publication November 8, 2011; accepted February 3, From the *Department of Internal Medicine, Gatroenterology Unit, University of Genoa, Genoa; wgastroenterology Unit, University of Parma, Parma, Italy. M.F. D.B. have contributed equally to the article. M.F. D.B.: writing the manuscript, contributed to data acquisition, participated in the statistical analysis; A.P., J.F., E.S.: designed the study contributed to data acquisition; L.B. A.M.: contributed to patient management; F.D.M., P.D., V.S.: participated in the writing of the manuscript data acquisition. All authors have seen approved the final version of the manuscript. The authors declare that they have nothing to disclose. Reprints: Vincenzo Savarino, MD, Gastroenterology Unit, Department of Internal Medicine, University of Genoa, Viale Benedetto XV, no. 6, Genoa, Italy ( vsavarin@unige.it). Copyright r 2013 by Lippincott Williams & Wilkins Lactose intolerance (or hypolactasia) is a common cause of gastrointestinal symptoms worldwide. Its prevalence is high throughout the world varies considerably among various ethnic groups. In South America, Africa, Asia, rates of lactose intolerance are >50%. 1 In the United States, the prevalence is 15% among whites, 53% among Hispanic Americans, 80% among Afroamericans. 2 In Europe, it varies from 2% in Scinavian countries to 70% in South Italy. 3 Lactose intolerance in most cases results from the inability to digest lactose, the predominant sugar of milk. This inability is caused by a shortage of the enzyme lactase, phlorizin hydrolase, which is located in the brush border (microvilli) of the small intestine enterocyte. It is a b-galactosidase that breaks down milk sugar (lactose) into simpler forms (glucose galactose) that can be absorbed into the blood stream. 4,5 If lactase enzyme is absent or deficient (hypolactasia), unabsorbed sugars osmotically attract fluid into the bowel lumen. In addition, lactose is fermented by colonic bacteria, with the production of gas monosaccharides that cannot be absorbed, thus increasing the osmotic pressure drawing more fluid into the bowel. 6 This fact, in some subjects, leads to symptoms of lactose intolerance, which are mainly represented by abdominal pain, bloating, flatus, diarrhea, borborygmi. Besides digestive complaints, systemic extraintestinal symptoms have been observed in a certain number of patients after intake of lactose, such as headache, fatigue, joint muscle pain, loss of concentration, short-term memory loss, also allergic reactions. 7 9 Lactase activity reaches its peak at birth, then it starts to decrease (lactase nonpersistence) within the first few months of life, with a continuous decline in lactase during the lifetime with the majority of people developing lactose insufficiency by adolescence. In humans, approximately 30% of the population has the so-called lactase persistence, that is, continued lactase activity beyond weaning into adulthood. 4 It is important to say that only 50% of lactase activity is necessary for effective utilization of lactose without symptoms of intolerance, moreover, up to 70% of the world population has lactase nonpersistence, but not all of them are intolerant to lactose. 4,5 Different methods can be used to diagnose lactose malabsorption. At present, the biochemical disaccharidase assay is the gold stard diagnostic test for hypolactasia. 10,11 However, it is expensive, invasive, results are obtained after a long delay. Genetic testing for lactase polymorphism has a high accuracy in predicting lactase J Clin Gastroenterol Volume 47, Number 2, February 2013

2 J Clin Gastroenterol Volume 47, Number 2, February 2013 Lactose Breath Test Quick Test persistence/nonpersistence, but it is expensive does not indicate the lactase activity at the moment the subject is tested. 10,11 Both tests are cumbersome in clinical practice. The lactose hydrogen breath test is actually considered to be the best tool to diagnose lactose intolerance because it is noninvasive, easy to perform, cost-effective. 4 Its main limitation is the nonoptimal sensitivity, with a certain percentage of false-negative results (up to 20%). This is because many subjects have a predominant population of methane-producing bacteria in the bowel, which use hydrogen to reduce carbon dioxide to methane. 4 Also, the orocecal transit time is an important factor to consider as it may influence the results of the examination. In fact, it is well known that in investigations using lactose breath test (LBT), the methodology may affect the sensitivity of the test 12,13 therefore it should be stardized. The quick lactase test is a new method for endoscopic diagnosis of hypolactasia that consists in performing a colorimetric reaction on duodenal biopsies to provide a semiquantitative evaluation of lactase activity. 14 The aim of the study was to compare the diagnostic accuracy of LBT lactose quick test (LQT) in patients with typical symptoms of lactose intolerance to assess the ability of LBT LQT to predict the clinical response to a free-lactose diet in symptomatic patients, who were positive to the above tests. MATERIALS AND METHODS Patients Fifty-one unselected consecutive patients (15 male, 36 female; mean age 47 ± 14 y) referred to the Gastroenterology Units of University of Genoa University of Parma were enrolled in the prospective study from December 2009 to December They presented bloating, flatus, abdominal pain, diarrhea after the introduction of milk or dairy products. Informed consent was obtained from all the participants. The study was performed in accordance with the Declaration of Helsinki, approved by the respective Ethics Committees. All patients underwent both stard LBT upper gastrointestinal endoscopy with biopsies for LQT histologic analysis within 1 week from each other. Two different investigators analyzed the tests, they were blinded to the results of the other. Glucose breath test (GBT) was performed in all patients who were LBT positive LQT negative (false positive with LBT) to rule out the presence of small intestinal bacterial overgrowth (SIBO) as a cause of false-positive LBT. All patients, except those with celiac disease (confirmed at histologic examination) or SIBO, were treated with a lactose-free diet for 1 month, regardless of the method assessing the diagnosis of lactose malabsorption. Patients received dietician support a diet sheet containing a list of permitted excluded foods. Lactose intolerance was diagnosed by considering both clinical instrumental data: the presence of gastrointestinal symptoms after milk ingestion one or both tests positive for lactose malabsorption. We further evaluated the clinical improvement after a lactose-free diet. Lactose Breath Test Patients were asked to have a carbohydrate-restricted dinner on the day before the test to be fasting for at least 12 hours on the testing day. Before starting the test, patients did a mouthwash with 20 ml of chlorexidine 0.05%. They were asked not to smoke not to perform physical exercise for 30 minutes before during the test. A basal sample was collected immediately before lactose ingestion. A baseline H 2 value >10 ppm was defined as an exclusion criterion. Then, a dose of 25 g of lactose in 250 ml of water was administered; breath samples were taken every 30 minutes for 4 hours immediately evaluated for H 2 using a model Quintron Gas Chromatograph (Quintron Instrument Company, Milwaukee, WI). The measurements were then analyzed. Results were expressed as part per million (ppm). LBT was considered positive for lactose malabsorption when an increase in H 2 value of >20 ppm over the baseline value was registered. 10 The same procedure was used for the detection of CH 4 with a dedicated gas chromatograph. Any CH 4 value >5 ppm was used as a cutoff to define patients as methane producers. GBT This test was performed at least 1 week after LBT with the same preparation; patients took a 20% solution of glucose in 250 ml of water immediately after the basal sample; breath samples were taken every 15 minutes for 2 hours analyzed using a gas chromatograph; a baseline H 2 value >10 ppm was defined as an exclusion criterion; GBT was considered positive for SIBO when an increase in H 2 value of >12 ppm over the baseline was registered. 15 Any CH 4 >5 ppm was used as a cutoff to define patients as methane producers. Endoscopy Lactose Quick Test During endoscopy, 2 postbulbar duodenal biopsies were taken from each patient to perform the Lactose Intolerance Quick test (Biohit, Helsinki, Finl). Biopsies were also taken from the stomach the duodenum for histologic examination to detect the presence of other diseases responsible for symptoms of malabsorption. The biopsy specimens were examined immediately. This test is based on a colorimetric assay that evaluates the lactase activity: the color development in the test liquid after 20 minutes yields information on whether or not the lactase enzyme is present in the specimen. In case of a normal result, the color develops as the lactase enzyme of the biopsy specimen breaks down the milk sugar added to the test buffer. However, if there is no reaction or slight color reaction, it means that lactase activity is lacking or reduced that the test is positive. The total reaction time lasts for 20 minutes the test is performed in 2 steps. In the first 15 minutes, the lactase enzyme in the biopsy specimen breaks down the lactose substrate into monosaccharides glucose galactose. In the second step that lasts for 5 minutes (signal reaction step), the amount of glucose is detected using a chromogen solution the signal reaction solution, resulting in the formation of a colored compound. To quantify the QLT, a color chart is constructed: no color reaction corresponds to a lactase activity <10 U/g protein (severe hypolactasia); a mild blue reaction corresponds to 10 to 30 U/g protein (mild hypolactasia); a deep blue reaction corresponds to 30 U/g protein or more (normolactasia). Histologic examination of the duodenal biopsies was performed in all patients to evaluate the presence of mucosal damage or inflammatory damage leading to a secondary hypolactasia, such as celiac or Whipple disease eosinophilic gastroenteritis. r 2013 Lippincott Williams & Wilkins 149

3 Furnari et al J Clin Gastroenterol Volume 47, Number 2, February 2013 Questionnaire All patients were asked to fill a validated questionnaire of their symptoms [Global Symptomatic Score (GSS)] under basal conditions after a lactose-free diet for 1 month to evaluate the response to therapy. This questionnaire evaluated the presence the intensity of symptoms (constipation, diarrhea, bloating, abdominal pain, flatus, borborygmi, nausea, vomiting) scored from 0 (absence) to 3 (severe). A GSS improvement Z75% was considered a significant clinical response to the lactose-free diet. Patients were also asked to report the possible onset of symptoms during the LBT every 15 minutes while collecting the samples. Moreover, patients were contacted by phone the day after the examination to register late onset of symptoms. Patients were blinded about the results of tests they performed. Statistical Analysis Demographic clinical characteristics of the study population are shown as mean values, ranges, rates. Furthermore, the ability of the LBT the lactose quick test to identify subjects responding not responding to the lactose-free diet was shown as positive negative predictive values (NPVs), accordance between the 2 tests, diagnostic accuracy, 95% confidence intervals. A statistical analysis was performed with GRAPHPAD Software (QuickCalcs, San Diego, CA) with GNU Software (PSPP, Boston, MA). RESULTS Table 1 shows the main clinical characteristics of our patients. We diagnosed lactose malabsorption in 31 of the 51 patients with LBT in 37 of the 51 with LQT (P = 0.29). All subjects with severe hypolactasia on LQT (5/37) also had a positive LBT. Twenty-nine subjects were positive to both LBT LQT. Two of them had celiac disease diagnosed with histologic examination serologic tests. Thus, they were asked to follow a gluten-free diet were excluded from the evaluation of the efficacy of the lactose-free diet. One subject of the remaining 27 was asymptomatic after lactose intake. Twelve subjects were negative to both LBT LQT, whereas 2 patients had positive LBT negative LQT were diagnosed as SIBO positive using GBT, so they were also excluded from the evaluation of the lactose-free diet improved after an antibiotic course with rifaximin. Eight patients had negative LBT positive LQT, which showed a mild hypolactasia. Two of them presented an exclusive CH 4 production during LBT. CH 4 values did TABLE 1. Results of the 2 Tests in Our Study Population LBT+ LQT+ LBT LQT LBT+ LQT LBT LQT+ Patients (n) Celiac disease SIBO Lactose intolerance LBT, lactose breath test; LQT, lactose quick test; SIBO, small intestinal bacterial overgrowth. TABLE 2. Accuracy of Lactose Breath Test Lactose Quick Test in Diagnosing Lactose Intolerance Test Sens Spec LBT 76.5% 92.3% CI 95 : CI 95 : LQT 100% 92.3% CI 95 : PPV (%) NPV (%) CI 95 indicates confidence interval 95%; LBT, lactose breath test; LQT, lactose quick test; NPV, negative predictive value; PPV, positive predictive value; Sens, sensitivity; Spec, specificity. not increase or barely increased with respect to the baseline value after oral lactose intake. The overall diagnostic accuracy of the 2 tests is reported in Table 2. LQT is characterized by the same specificity as LBT, whereas the sensitivity NPV are better. The concordance rate between the 2 tests was 83.0% (P = 0.05). All patients, with the exception of those with celiac disease or SIBO, performed a lactose-free diet for 1 month without knowing the results of the 2 tests. Then, they completed another questionnaire at the end of the treatment, to evaluate the efficacy of the diet: 26 of the 27 patients LBT+/ LQT+ showed a significant improvement of symptoms [GSS:12 (6 to 15) vs. 3 (0 to 3); P < 0.01]; the 12 patients who were LBT LQT did not improve after diet [GSS:12 (10 to 13) vs. 11 (10 to 12), P = NS]; finally, all patients who were LBT LQT + showed a significant clinical improvement after a lactose-free diet [GSS:11 (7 to 15) vs. 2 (0 to 3), P < 0.01]. As to the ability of the 2 tests to predict the response to a lactose-free diet, LBT was successful in 38/47 cases (80.8%) LQT in 46/47cases (97.8%; P = 0.03). No adverse events were reported during the study. DISCUSSION In this prospective study, we compared LQT on duodenal biopsies with LBT to assess lactase deficiency in unselected consecutive patients referring symptoms of lactose intolerance. Nowadays, no gold stard is available for the diagnosis of lactose malabsorption. Therefore, in our study, the diagnosis of lactose intolerance was based on an overall evaluation of all investigations patients underwent: the presence of gastrointestinal symptoms after milk ingestion one or both tests positive for lactose malabsorption. We further evaluated the clinical improvement after a lactose-free diet to reinforce our diagnostic criteria. We found that both tests were able to identify patients with this disorder with a good agreement, the concordance rate being 83%. This finding confirms the results obtained by Ojetti et al, 14 who evaluated 50 patients undergoing both LBT LQT, observed that the concordance rate between the 2 tests was 81%: this value increased up to 96%, when considering CH 4 production also. Unlike the previous study, however, our patients who were positive to LBT alone also underwent GBT to rule out SIBO as a possible cause of a false-positive result. This procedure allowed us to exclude 2 false-positive cases obtained by LBT to increase the specificity of the test r 2013 Lippincott Williams & Wilkins

4 J Clin Gastroenterol Volume 47, Number 2, February 2013 Lactose Breath Test Quick Test Moreover, we assessed the ability of the 2 tests in predicting accurately the clinical response to a lactose-free diet. We found that all subjects positive to both LBT LQT had a good response to the lactose-free diet, with the exception of one. For this patient, it could be argued that the presence of lactose malabsorbion without lactose intolerance related clinical manifestations might be due to a concomitant functional disorder, such as irritable bowel syndrome. In contrast, those who were negative to both tests had no benefit from the diet. An important observation was that 8 patients who were LBT LQT+ also had a good response to the lactose-free diet. Although the clinical response to the lactose-free diet cannot be regarded as the gold stard test for the diagnosis of lactose intolerance, this result suggests that the sensitivity of LBT is lower than that of LQT in predicting the response to therapy, because 8 falsely negative patients with the former test would have not received a potentially beneficial treatment. At present, the most common easy method used to diagnose hypolactasia is H 2 BT. In a recent study, Pohl et al 19 found an excellent agreement between H 2 BT genetic testing, which can be considered as the best tool to assess lactose deficiency. The sensitivity specificity were similar between the 2 tests, with 4% to 6% of discrepant results only. The major advantage of LBT is its noninvasiveness, therefore, it is highly accepted by patients. However, its main disadvantages are the inability to indicate the grade of hypolactasia (mild, moderate, or severe), above all, the low sensitivity. In fact, several studies have already demonstrated that LBT often yields false-negative results 14,20 this certainly reduces the ability to predict the response to the lactose-free diet. The last point is very important because it renders it difficult to make a differential diagnosis of diseases characterized by the same symptoms, such as irritable bowel syndrome, for which a lactose-free diet is not useful. Finding a certain number of false-negative results with subsequent low NPV is often caused by the fact that a variable number of patients fail to excrete appreciable H 2 during colonic carbohydrate fermentation. These low H 2 excretors frequently have a higher breath CH 4 concentration. In fact, the synthesis of CH 4 requires large amounts of H 2, so the increase of CH 4 in the expiratory air reduces the production of H 2. For this reason, Houde Forup 21 suggest to assess the gas excretion as the sum of CH 4 concentration multiplied by 2 plus H 2 concentration (CH 4 2 ppm + H 2 ppm). In our study, 2 of the 8 (25%) patients with a negative LBT a positive LQT, who improved after a lactose-free diet, showed exclusive methane excretion. Therefore, we suggest that methane should be assessed routinely during lactose intolerance breath testing. Another limitation of LBT is related to the influence of the orocecal transit time, which is characterized by a considerable individual variability. Patients with a slow transit time should probably have a more prolonged duration of the test, to avoid false-negative results. Corazza et al 13 analyzed the results of 352 LBT with a duration of 4 hours, to assess whether the results after 2 hours have the same accuracy as those after 4 hours. In the 208 subjects who were lactose intolerant, the median value of the changes of H 2 concentration was seen 3 a half hours after the load of lactose. Most patients reached the predefined cutoff value (> 20 ppm) during the first 2 hours, but 37% became positive only after this longer time period. Therefore, they suggested that LBT must be prolonged almost for 4 hours to obtain a higher accuracy this was carried out in our study. Also, the optimal number of breath samples has been debated considerably in the medical literature. In the study by Abramowitz et al, 22 the authors argue that values at minutes are sufficient to define lactose malabsorption, thus removing the need for multiple samples. In contrast, Di Camillo et al 3 demonstrated that a 3-sample test (0, 120, 180 min) may allow us to save time without loss of sensitivity. Our study demonstrates that LQT is characterized by the same accuracy of LBT in diagnosing hypolactasia, but it has the advantage of also defining the grade of this deficiency. Our results are in agreement with those reported in the study by Kuokkanen et al, 23 who investigated the usefulness of the new LQT by comparing it with the genetic testing (assaying the C/T variant). They showed that LQT identifies patients with severe hypolactasia with high accuracy. In fact, when the results of LQT were compared with C/T polymorphism, the sensitivity the specificity were 100%. In the same investigation, the comparison with biochemical assays of disaccharidase activity by PCR showed that the sensitivity the specificity were 95% 100%, respectively. Therefore, the study by Kuokkanen colleagues sustains our findings that a positive LQT indicates severe hypolactasia with a very high accuracy, whereas a negative LQT indicates normolactasia with a significant level of sensitivity specificity. LQT has the main disadvantage of being invasive, as an upper endoscopy is necessary to take biopsies, therefore, this examination is poorly accepted by patients. If we also add the major cost of this test in comparison with LBT, it is not reasonable to propose this test as the first-line investigation to diagnose lactose intolerance. However, in a subset of patients with self-reported lactose intolerance who are referred to upper gastrointestinal endoscopy for any reason, LQT should be used as the best tool to diagnose or rule out lactose malabsorption. In conclusion, our study demonstrates that LBT is characterized by good specificity, but not optimal sensitivity for diagnosing hypolactasia. The new LQT has a diagnostic accuracy similar to LBT shows a greater ability to predict the response to a lactose-free diet, as it detects more patients with mild hypolactasia than LBT. However, the cost invasiveness of LQT limit its clinical application as the first-line investigation to diagnose lactose malabsorption. REFERENCES 1. Scrimshaw NS, Murray EB. Prevalence of lactose maldigestion. Am J ClinNutr. 1998;48: Law D, Conklin J, Pimentel M. Lactose Intolerance the Role of the Lactose Breath Test. Am J Gastroenterol. 2010;105: Di Camillo M, Marinaro V, Argnani F, et al. Hydrogen breath test for the diagnosis of lactose malabsorption: the importance of timing number of breath samples. Can J Gastroenterol. 2006;20: Lomer MCE, Parkes GC, Serson JD. Review article: lactose intolerance in clinical practice myths realities. Aliment Pharmacol Ther. 2008;27: Vesa TH, Marteau P, Korpela R. Lactose intolerance. JAm Coll Nutr. 2000;19:165S 175SS. r 2013 Lippincott Williams & Wilkins 151

5 Furnari et al J Clin Gastroenterol Volume 47, Number 2, February Swagerty DL, Walling AD, Klein RM. Lactose intolerance. Am Fam Phisician. 2002;65: Chaudhuri A. Lactose intolerance neuromuscular symptoms. Lancet. 2000;356: Matthews SB, Campbell AK. When sugar is not so sweet. Lancet. 2000;355: Matthews SB, Waud JP, Roberts AG, et al. Systemic lactose intolerance: a new perspective on an old problem. Postgrad Med J. 2005;81: Gasbarrini A, Corazza GR, Gasbarrini G, et al. Methodology indications of H2-breath testing in gastrointestinal diseases: the Rome Consensus Conference. Aliment Pharmacol Ther. 2009;29: Rao P, Rao N, Jordinson M, et al. Comparison of quick point of care test for small bowel hypolactasia with biochemical lactase assay in children. J Pediatr Gastroenterol Nutr. 2012;54: Di Stefano M, Missanelli A, Miceli E, et al. Hydrogen breath test in the diagnosis of lactose malabsorption: accuracy of new versus conventional criteria. J Lab Clin Med. 2004;144: Corazza GR, Sorge M, Strocchi A, et al. Methodology of the H2 breath test. II. Importance of the test duration in the diagnosis of carbohydrate malabsorption. Ital J Gastroenterol. 1990;22: Ojetti V, LaMura R, Zocco MA, et al. New test for the diagnosis of duodenal hypolactasia. Dig Dis Sci. 2008;53: Parodi A, Dulbecco P, Savarino E, et al. Positive glucose breath testing is more prevalent in patients with IBS-like symptoms compared with controls of similar age gender distribution. J Clin Gastroenterol. 2009;43: Furnari M, Parodi A, Gemignani L, et al. Clinical trial: the combination of rifaximin with partially hydrolysed guar gum is more effective than rifaximin alone in eradicating small intestinal bacterial overgrowth. Aliment Pharmacol Ther. 2010; 32: Parodi A, Paolino S, Greco A, et al. Small intestinal bacterial overgrowth in rosacea: clinical effectiveness of its eradication. Clin Gastroenterol Hepatol. 2008;6: Parodi A, Sessarego M, Greco A, et al. Small intestinal bacterial overgrowth in patients suffering from scleroderma: clinical effectiveness of its eradication. Am J Gastroenterol. 2008;103: Pohl D, Savarino E, Hersberger M, et al. Excellent agreement between genetic hydrogen breath test for lactase deficiency the role of extended symptom assessment. Br J Nutr. 2010;104: Arola H. Diagnosis of hypolactasia lactose malabsorption. Sc J Gastroenterol. 1994;S202: Houde O, Forup PG. A comparison of diagnostic tests for lactose malabsorption which one is the best? BMC Gastroenterol. 2009;9: Abramowitz A, Granot E, Tamir I, et al. Two-hour lactose breath hydrogen test. J Pediatr Gastroenterol Nutr. 1986;5: Kuokkanen M, Myllyniemi M, Vauhkonen M, et al. A biopsybased quick test in the diagnosis of duodenal hypolactasia in upper gastrointestinal endoscopy. Endoscopy. 2006;38: r 2013 Lippincott Williams & Wilkins