A standardized milk tolerance test.

Inability to hydrolyze lactose does not always cause symptoms. The lactose tolerance test commonly used in diagnosis pinpoints the biochemical anomaly but does not establish whether it causes a functional disability. I therefore compared a milk tolerance test (500 ml milk) with the standard lactose tolerance test in 40 healthy adult volunteers for rise in blood sugar. A maximum glucose rise of 9 mg/100 ml or less indicated lactose malabsorption. Only one subject was misclassified by the milk tolerance test when compared with the lactose tolerance test (specificity 91.7%; sensitivity 100%). The test not only reproduces the worst symptoms that the subject is likely to suffer due to usual milk intake, but also accurately identifies the lactose malabsorber, thus yielding more information than the standard lactose tolerance test.