“…Through the years there have been numerous modifications to the test meal, including the use of citric acid alone before administering the urea [37,62,67,79,84,85,97] , or mixed with the 13 C-urea at the time of administration [43][44][45]88,91,98] , or as a presentation in combination with the 13 C-urea [42,61,72,94,99] . Several alternatives to citric acid have also been tested, including orange juice [43,49,67,90,95] and apple juice [100] , as well as other types of food such as milk [48,58,101,102] and a pudding test meal [34,46] , and even water [41,103] . As shown in Table 3, the majority of the test meals have provided reliable results.…”