The Illinois State Police opened 2001 with an updated rule for testing drunk drivers and those under the influence of other illegal substances.

Capt. Dave Sanders said state police now can use blood serum, or the clear liquid that separates from fully clotted blood, to measure the blood-alcohol content of some people charged with DUI.

“We had the joint responsibility of the public health department in regulating the blood-alcohol content in DUI arrests,” Sanders said.

Police use serum in cases where there has been an accident and a driver who may be under the influence is at the hospital. In such cases, the only way to check the alcohol content may be through serum extraction. Through a division formula, or “conversion factor,” serum is used to project a driver’s actual blood-alcohol content without having to obtain a breathalizer test or study an entire blood sample.

The rule was made official for 150 days on Jan. 1 and is scheduled to become permanent by Feb. 1.

Serum testing, according to a Jan. 9 Chicago Tribune article, has been used at hospitals and by police long before the rule was set in stone.

Sanders said it was important to enact the rule officially for legal purposes.

“Experts testify for conversion factors in court,” he said. “It’s been a long process. It was placed in to give some guidance. It reflects the change in rules and technology.”

Blood serum tests are admitted to Illinois courts on a case-by-case basis, and some believe the testing is not as trustworthy as a whole blood test, the Tribune reported. Because serum is more watery than complete blood, it has far higher alcohol concentrations that must be adjusted.

“The serum level is an estimation, so it’s not going to be as accurate as analyzing whole blood itself,” Ron Kucharik, chief toxicologist for the state police, told the Tribune.

But Dr. Robert Kirschner, a former deputy Cook County medical examiner, said in the article that serum testing should be used in court cases where the alcohol content of a victim is “well beyond legal limits.”

“The only time you’re going to find difficulties would be in that borderline area,” he said.

The legal blood-alcohol limit for Illinois drivers is .08.

Part 1286 of the 20 Illinois Administrative Code of the Illinois State Police includes rules for testing breath, blood and urine for alcohol, drugs and other intoxicating compounds.