Lactose is commonly used as a cutting agent in illicit drugs. Currently, presumptive field color

test kits for illicit drugs do not test for the presence of lactose or other cutting agents. A method

was developed to detect lactose on a paper-based test card. A three-enzyme system comprised of

lactase, glucose oxidase, and peroxidase was used to break down lactose into peroxide, which

was then detected with a redox indicator. The test can detect lactose concentrations as low as 5%

in solid samples and shows no interference when lactose is mixed with illicit drugs or

commercial pharmaceuticals. Prepared test cards were stable on the shelf for up to five months.

In a blinded study of samples composed of mixtures of heroin, methamphetamine, cocaine HCl,

crack cocaine, fillers, and lactose, the sensitivity for detection of lactose across three readers was

100% and specificity was 96.4% (n=96). When this test was incorporated into a 12-lane test card

for the detection of illicit drugs, readers were correctly able to identify the illicit drug and the

presence of lactose with 99.3% sensitivity and 100% specificity (n=54). This test is a robust and

affordable way to detect lactose in illicit drug samples.