Introduction: Recent reports suggest that abnormalities of lactulose breath testing (LBT) are common in patients with irritable bowel syndrome (IBS), although the criteria for abnormal studies are poorly validated, and controlled comparisons are limited. The goal of this study was to determine the prevalence of abnormal LBT using the previously published criteria in both IBS patients and healthy controls, as well as to determine the prevalence and symptom association with methane (CH(4)) and hydrogen (H(2)) productions during LBT.
Methods: Consecutive LBT from patients meeting Rome II criteria for IBS and healthy control subjects were examined. Patients listed their most bothersome digestive symptom at the start of the test. LBT was performed using 10 g of lactulose mixed in 240 mL of water, and breath samples collected every 20 min for a 180-min period. Both breath H(2) and CH(4) were measured. LBT was considered positive if it met any of the previously published criteria: (a) breath H(2) of > 20 parts per million (ppm), (b) increase in breath H(2) in < 90 min, (c) dual H(2) peaks (12-ppm increase over baseline with a decrease of > or = 5 ppm before 2nd peak), and (d) breath CH(4) of > 1 ppm.
Results: In total, 224 patients with IBS and 40 controls were studied. Twenty percent of IBS patients were CH(4)(+) compared with 15% of controls. CH(4)(+) IBS patients were significantly more likely than CH(4)(-) IBS patients to have constipation, and significantly less likely to have diarrhea; however, the association did not hold for symptoms of bloating or pain. Patients and controls did not differ significantly with respect to the frequency of a positive study defined by increase in breath H(2) in < 90 min (121 per 180 vs 26 per 40, P = 0.79), increase in breath H(2) of > 20 ppm (92 per 180 vs 24 per 40, P= 0.31), or dual peaks (25 per 180 vs 9 per 40, P = 0.17).
Conclusions: The majority of patients with IBS and healthy subjects meet criteria for an "abnormal" LBT using previously published test criteria, and groups are not discriminated using this diagnostic method. Similarly, while CH(4) production was associated with constipation among IBS patients, the prevalence of CH(4)-positive subjects did not significantly differ between IBS patients and controls. The utility of LBT, in its current form as a diagnostic tool in IBS requires critical reappraisal.