The Lactulose Assay Kit  will measure lactulose in most samples however it is the sample preparation prior to the Enzymatic Determination Reaction that is important.  Megazyme has only tested milk-based samples, however most samples that do not contain high protein levels may work using the same standard procedure as described in the K-LACTUL data booklet.  Samples containing very high levels of free fructose may not work.

Product Page (K-LACTUL)