The K-LACGAR assay kit does include a procedure for samples containing high levels of sugars (see Procedure B on page 7 of the Lactose/Galactose (Rapid) (K-LACGAR) Data Booklet.
As an alternative we have Lactose Assay kit (K-LOLAC ) that is highly specific, sensitive and sequential meaning that it is performed in a single assay instead of 2 assays like K-LACGAR.
K-LOLAC provides a much improved assay for measuring low lactose levels in samples and as the measurement is based on glucose released from the lactose hydrolysis a pre-step includes removal of free glucose.