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OLYMPIA, Wash. -- How is a motorist stopped for DUI in Washington supposed to know when blood THC content has reached five nanograms per liter to break a new law?

The legal blood alcohol limit for driving in Washington state is 0.08.

Now, there's another number to consider for driving while under the influence of marijuana.

Five.

The legal limit is five nanograms of THC per millimeter of blood. THCis the active ingredient in pot.

There isn't a breath test for THC and while oral fluid testing could be done in the future, blood testing is the only option in Washington right now.

The state toxicology lab already tests for THC in about 1,000 drug-related DUI cases a year, but the limit is new.

The blood test isn't simple. It involves 39 different steps from when the blood is drawn to the testing of 50 microliters of clear fluid for THC.

In the lab, the testing can take more than two weeks, which could be a problem in court.

Longtime DUIattorney John Fox questions the constitutionality of the new marijuana law, because pot smokers have no way to test their levels.

As marijuana smokers test their new freedom, the new DUIlab will face major tests of its own, on the highways, in the lab, and in the courts.

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