Conceptual basis of the diagnosis of lactose intolerance, hypolactasia and lactose maldigestion

Abstract

The pathophysiology of hypolactasia, lactose maldigestion and lactose intolerance are reviewed to clarify conceptual confusions and convey precise diagnoses. Lactase is the enzyme that helps to digest milk lactose, releasing galactose and glucose. While in adults with primary adult-type hypolactasia phenotype, the enzyme activity reaches 10% of the maximum observed in childhood, in individuals with lactase persistence phenotype, the activity remains high. In Europeans, phenotypes are closely associated with C/T-13910polymorphism; therefore, genotyping may be used as a diagnostic test. However, this is not possible in Colombian Caribbean population due to the existence of moderate association genotype-phenotype. The direct diagnosis of hypolactasia/persistence consists of an enzymatic method; a lactase/sacarase index<0.3 indicates hypolactasia. Lactose maldigestion, the inability to digest a certain amount of lactose, is evaluated through application of either breath hydrogen or a lactose intolerance test, which allow to infer whether the individual might be a lactase persistent (digester) or hypolactasic (maldigester). Lactose intolerance is the clinical digestive syndrome that may appear following ingestion of lactose, due to hypolactasia or to glucose-galactose malabsorption. A subject is considered to be intolerant to lactose when symptoms disappear as milk is excluded from the diet for two weeks, and reappear upon its restoration as part of his diet. “Lactose malabsorption” is a physiological misnomer because lactose is not absorbed as such. Hypolactasia, lactose maldigestion and lactose intolerance are not synonyms. They involve different pathophysiological states, which are not always associated with each other. Understanding each of these three concepts is critical for a correct diagnosis.