Both limit values differ from each other due to the amount of methane and hydrogen that bacterias are producing during the metabolisation of lactose. Normally, there isn't any or there is some methane produced - even with a lactose-intolerance. Only a few of people have been observed who are having both methane and hydrogen with a lactose-intolerance. In order to cover all affected people we measure both values. Most of the people show little amounts of hydrogen and no methane at all in the exhaled air. Once either one or both of the values are exceed, it can be a lactose-intolerance. That is why both values are equally important. If only one of the both values of the gases shows values, this only means that the bacteria in the gut are producing the gas during metabolisation. In any case this indicates a lactose-intolerance.