The hydrogen (H
2) breath test is a non-invasive investigation used to diagnose lactose intolerance (LI). Patients with LI may also expire increased amounts of methane (CH
4) during a lactose test. The aim of this study is to evaluate the
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The hydrogen (H
2) breath test is a non-invasive investigation used to diagnose lactose intolerance (LI). Patients with LI may also expire increased amounts of methane (CH
4) during a lactose test. The aim of this study is to evaluate the contribution of CH
4 measurements. We tested 209 children (1–17 years old) with symptoms suggesting LI with lactose H
2 and CH
4 breath tests. The result was positive when the H
2 excretion exceeded 20 parts per million (ppm) and the CH
4 was 10 ppm above the baseline. A clinician, blinded for the results of the breath test, registered the symptoms. Of the patient population, 101/209 (48%) were negative for both H
2 and CH
4; 96/209 (46%) had a positive H
2 breath test result; 31/96 (32%) were also positive for CH
4; 12/209 (6%) patients were only positive for CH
4. The majority of hydrogen producers showed symptoms, whereas this was only the case in half of the H
2-negative CH
4 producers. Almost all patients treated with a lactose-poor diet reported significant symptom improvement. These results indicate that CH
4 measurements may possibly be of additional value for the diagnosis of LI, since 5.7% of patients were negative for H
2 and positive for CH
4, and half of them experienced symptoms during the test.
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