Hawaii employees testing positive for marijuana use climbed 30 percent in the fourth quarter of 2010 compared with a year earlier, according to Diagnostic Laboratory Services Inc.

The drug-testing company said 3.5 percent of the workers tested during the quarter had used marijuana, up from 2.7 percent a year ago. DLS’ quarterly sample size typically includes between 7,000 to 10,000 drug tests.

The number testing positive was "probably the highest" in the last eight to 10 years, said Carl Linden, scientific director of toxicology for DLS. Linden, 59, who has been conducting drug tests in Hawaii since 1980, said he does not know what caused the jump in positive marijuana results last quarter.

Use of opiates and amphetamines was little changed in the fourth quarter at 0.2 percent and 1.0 percent, respectively. Cocaine use was up slightly to 0.3 percent from a 0.2 percent a year earlier.

The number of workers testing positive for substance abuse is likely much smaller than the actual number using drugs, Linden said. That number could be 10 percent to 20 percent, he said. Many people, knowing they will likely be tested for drugs when they get a new job, probably abstain from using them to pass the test, Linden said.

DLS began testing for synthetic urine for the first time last year. In the fourth quarter, 2.3 percent of those tested were found to be using synthetic urine.

The use of synthetic urine will likely decline as word gets out that DLS is testing for it, Linden said.

Synthetic urine is sold online. Users heat it in a microwave oven and keep it warm with a hand-warming pack. They keep it concealed until the sample is turned in, Linden said. Some use a temperature strip to make sure the urine is in the acceptable 95- to 98-degree temperature range, he said.

DLS said 7.3 percent of those tested in the fourth quarter were either positive for one of the tested drugs or used synthetic urine.