Fructose malabsorption – the patient takes a base reading of hydrogen levels in his/her breath. The patient is then given 25-35g of fructose, and then required to take readings every 15, 30 or 60 minutes for three - five hours. The basis of the test is a failure to absorb the given sugar, which is then metabolized by bacteria that give off either hydrogen or methane. Therefore, the more gas that is produced, the less absorption has occurred. If the level of hydrogen rises above 20 ppm (parts per million) over the lowest preceding value within the test period, the patient is typically diagnosed as a fructose malabsorber. If the patient produces methane then the parts per million for the methane typically rises 12 ppm over the lowest preceding value to be considered positive. If the patient produces both hydrogen and methane then the values are typically added together and the mean of the numbers is used to determine positive results, usually 15 ppm over the lowest preceding value.