Hawai'i's two largest drug testing companies continue to catch employees and potential employees tampering with urine samples to beat drug screens, but nevertheless believe workforce drug use is falling in the Islands.

Sometimes several times per day, officials at Diagnostic Laboratory Services Inc. collect urine samples with temperatures below or above normal, suggesting the sample does not belong to the employee being tested. And last week the company collected an employee's urine containing so much bleach — apparently designed to invalidate the sample — "that the collector could smell the bleach and it started bleaching out the label," said Carl Linden, the company's scientific director of toxicology.

Despite continuing efforts by workers and job candidates to produce negative drug test results — or fuzz up the sample enough to invalidate the test — Clifford Wong believes drug use has fallen this year.

Wong is forensic toxicologist and lab director of Clinical Laboratories of Hawaii, which saw the percentage of positive tests fall from 7 percent in 2005 to 6.5 percent in the first quarter of 2006. Diagnostic Laboratory Services, which calls itself the Islands' largest drug testing company, saw the percentage of positive workplace drug tests drop from 5.2 percent in 2005 to 4.1 percent in the first quarter of 2006.

"So the optimistic outlook is that people are not taking drugs as much anymore," Wong said.

Both companies regularly monitor Internet sales of products and techniques aimed at falsifying drug tests — as well as products sold locally at nutrition stores and drug paraphernalia shops — and say nothing new has been introduced in the past five years.

At the same time, Clinical Laboratories of Hawaii has seen a change in questionable urine samples that suggests employees and future workers are realizing their doctored samples aren't fooling drug-testing companies, Wong said.

In 2003, Clinical Laboratories of Hawaii found that 10 percent of the urine specimens suspected of being diluted with water were actually positive for drugs — compared with 7 percent of all of the tested samples. Some people being tested for drug use drink large quantities of water in hopes of diluting their urine sample.

In 2004, only 8 percent of diluted samples tested positive — compared with 7.5 percent of all samples. Last year, the percentage of suspect samples testing positive dipped to 7.5 percent — compared with 6.8 percent of all samples.

"They know they're being tested and we are checking, so they are no longer trying to overload themselves on water," Wong said.

Linden of Diagnostic Laboratory Services keeps track of products such as teas and pills and other items that are ingested and sold for as much as $200. Some have to be ingested for as long as eight days to supposedly produce a negative drug test.

But none of the products alone has been proven to create a negative test for drug users, Linden said. And all require the person to stop using drugs and drink gallons of water, which alone could produce a negative result, or at least trigger a retest.

"With an eight-day program and drinking gallons of water, even if you do nothing, you'll probably cleanse your system," Linden said.

State and federal laws prohibit officials from monitoring employees in the restroom during a first-time drug test or strip-searching them for fake urine or additives.

So both Diagnostic Laboratory Services and Clinical Laboratories of Hawaii have workers show what's in their pockets, shut off water faucets to prevent someone from adding water to their urine sample, turn the toilet water blue, monitor the garbage for any discarded packages or vials and prevent them from flushing anything down the toilet.

Still, both companies continue to find urine samples tainted with iodine, bleach, peroxide and other additives that don't produce a negative test but at least create a tainted sample that will call for a retest later.

"They're desperate," Wong said. "They want to stop the test, and they'd rather have a question mark than a definite finger pointed at them with a truly positive result."

A few years ago, Linden even caught an airline employee who tried to pass off someone else's urine as his own.

The employee was suspected of drug use and was required to produce a urine sample while being monitored. Instead, he used a reservoir-tube-and-pump system hidden in his pants to try to produce someone else's urine as Linden watched.

Both companies also use sample containers outfitted with temperature strips that can tell whether a sample is too cool or too warm to have recently come from a human body. Even fake urine samples that have been heated by hand or held against the body will see the temperature rapidly drop, Wong said.

State and federal regulations don't allow for testing of hair samples, which are less reliable and more costly to test, both companies said.

While Hawai'i's largest drug-testing companies continue to crack down on bogus urine samples, Wong wants employers with drug policies to develop clearer guidelines on treating workers suspected of doctoring their tests.

"The majority of employees in Hawai'i do not have procedures in their drug testing policies on how to handle drug test results that involve an invalid result, a diluted result or an adultered result," Wong said. "Sometimes they just allow the person to go back in and retest without being observed. It really should be treated as a positive test result."

Companies that fire employees for suspect test results could get into legal trouble, Wong said, if their lack of drug testing policies leads to inconsistent treatment of workers.

"They face a possible wrongful dismissal suit," Wong said. "If it's spelled out in their policies, then it's a lot clearer."

Paul Saito, a member of the board of directors of the Hawai'i chapter of the Society for Human Resource Management and a labor and employment lawyer with Torkildson Katz Fonseca Moore & Hetherington, said more employers are advertising their drug testing policies to potential employees despite Hawai'i's low unemployment rate.

Advertising pre-employment drug tests — as well as any random tests — actually helps screen drug users from even applying, Saito said.

"You still want to hire qualified people and you don't want to hire people with problems," Saito said. "If you put up a little sign that says 'we drug test,' a lot of people just don't follow through. That's more of a benefit to the employer than drug testing."

Reach Dan Nakaso at dnakaso@honoluluadvertiser.com.