The number of Hawaii workers and job applicants testing positive for marijuana soared 25 percent in the first quarter compared with the same period a year earlier, according to a report released yesterday by Diagnostic Laboratory Services Inc.

Three percent of workers tested in the first three months of 2011 had used pot, up from 2.4 percent in the first quarter of 2010, the company said. The data were derived from 7,000 to 10,000 drug samples each quarter.

Meanwhile, the number of employees using amphetamines and opiates was flat year-over-year at 1.1 percent and 0.2 percent, respectively. Cocaine use rose greatly in the quarter to 0.3 percent from 0.2 percent the year before, the report showed.

"Typically it has to do often with availability — cocaine and amphetamine is more difficult to get," said Carl Linden, DLS scientific director of toxicology. "If one is a little more expensive or less available, you often see that type of switching back and forth."

Linden said many of the samples came from pre-employment tests, which means "there’s a high number of people that are not being hired."

"It could be of concern to companies that don’t do drug testing ’cause that’s where they’ll gravitate to," he said.

The report also showed that fewer workers used fake urine over the previous quarter. The drug-testing company started screening for synthetic urine late last year, so there is no year-over-year comparison.

Synthetic urine can be bought online and then heated in a microwave oven before the test and kept warm with a hand-warming pack. Synthetic urine use plunged 35 percent in the first quarter, to 1.5 percent, compared with 2.3 percent in the fourth quarter of 2010. A sample that shows synthetic urine was used but contains no drugs is reported as "invalid," and a new sample needs to be submitted.

DLS let it be known last year that it was testing for synthetic urine. The drop in synthetic urine use could, in part, be responsible for the increase in positive tests for marijuana and other drugs.

"As synthetic urine drops off you might see the drugs increasing because they’re not using synthetic urine," Linden said. "All substance abuse in the workplace is a cause for concern. There’s this percentage of abusers that is really ingrained in our society. It’s hard to get rid of."

The rise in positive drug tests in the first quarter of this year followed a similar increase a year ago. Workers testing positive for marijuana climbed 30 percent in the fourth quarter of 2010 compared with the same period in 2009.