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DENVER — The percentage of job applicants who are testing positive for drugs has hit a 10-year high, according to a study.

The Quest Diagnostics Drug Testing Index looked at nearly 11 million workforce drug test results in America and found an average of 4.2 percent of them were positive.

The average in Colorado was slightly higher — 4.7 percent.

“The last year that the positivity rate for urine drug tests in the combined U.S. workforce was at or above 4 percent was 2005, when it reached 4.1 percent,” researchers stated.

RELATED: Interactive map of positive urine drug tests

The report indicated the rate of amphetamine, marijuana and heroin detection has gone up each year for the past five years.

“Colorado and Washington, which became the first two states to legalize weed in 2012, showed the largest growth in positive tests,” The Cannabist reported.

The website pointed out that while marijuana is legal in several states, it is still illegal under federal law, and employers in the United States can refuse to hire anyone who consumes it — even if they have a prescription.