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Patients with predominant fasting methane production excrete less H(2) than LMP, after an oral load of lactose. The lower prevalence of severe lactose intolerance in PMP, as well as lower incidence of symptoms during the test, is, indeed, related to lower and slower H(2) excretion. The assumption that H(2) excretion is an effective means of quantifying the amount of malabsorbed carbohydrates is questionable in PMP. Methane-producing patients likely have a higher 'false negative' rate as compared to LMP after an oral load of lactose. Nonetheless, as symptoms are related to the amount of gas produced in the colon, HBT identifies patients with 'lactose intolerance', irrespective of the presence of lactose malabsorption, and helps in predicting the effect of lactose-restricted diet.

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Most patients with a positive HBT-25 normally absorb a lower dose of lactose and a strict lactose restriction on the basis of a "standard" HBT is, in most instances, unnecessary. Thus, the 25 g lactose tolerance test should probably be substituted by the 12.5 g test in the diagnosis of LI, and in providing dietary guidelines to patients with suspected lactose malabsorption/intolerance.