Reivindicaciones

1. Use of 4-galactosyl-xylose for the evaluation of the presence of xylose in urine, usable for in vivo evaluation of intestinal lactase as a diagnostic test of the deficiency of this enzyme, that comprises oral administration of an aqueous 4-galactosyl-xylose solution to an individual who has fasted for at least 8 hours and the evaluation of the amount of xylose present in urine. 2. Use according to claim 1, characterized in that the amount of xylose present in urine is calculated by means of the difference found between the measurement made in an aliquot coming from the total volume of urine collected after the intake of 4-galactosyl-xylose and the measurement made in an aliquot coming from the volume of basal urine collected immediately before the individual intakes this compound. 3. Use, according to claim 1, characterized in that the individual is a human being. 4. Use of 4-galactosyl-xylose to evaluate the presence of xylose in blood, useable for in vivo evaluation of intestinal lactase as a diagnostic test of the deficiency of this enzyme, which comprises oral administration of an aqueous 4-galactosyl-xylose solution to an individual who has fasted for at least 8 hours and the evaluation of the amount of xylose present in blood. 5. Use, according to claim 4, characterized in that the amount of xylose present in blood after the intake of 4-galactosyl-xylose can be evaluated in blood plasma or blood serum. 6. Use, according to claim 4, characterized in that the amount of xylose present in blood is calculated from the difference found between the measurement made in an aliquot of a fluid coming from a blood sample extracted from an individual after the intake of 4-galactosyl-xylose and the measurement made in an aliquot coming from a sample of basal blood extracted immediately before the intake of this compound by the individual. 7. Use according to claim 4, characterized in that the individual is a human being. 8. Use according to claims 1 and 4, characterized in that its use in human individuals permits carriers of intestinal lactase deficiency from being distinguished from those individuals who are allergic to some component of milk, but who do not have the deficiency of this enzyme.