"There is no relationship between what you find in a living person and what you find in a dead person," Bruce Goldberger, vice-president of the American Academy of Forensic Sciences and editor of the Journal of Analytical Toxicology told New Scientist.
To spread the word about the error, Steven Karch, a pathologist at the San Francisco Medical Examiner's office set up an ad hoc committee of senior forensic toxicologists and pathologists, including Goldberger, at the American Academy of Forensic Sciences conference in Dallas, Texas, last month. They plan to publish scientific papers in general medical journals highlighting the issue.
In living patients, the dose someone has been given is calculated by multiplying their body weight, the concentration of the drug in their blood and a constant called the "apparent volume of distribution" (Vd). The Vd is a fudge factor that averages out the distribution of a particular drug between tissues in the body. The Vd of any particular drug depends on how it interacts with an individual's cells.
Studies have suggested that the Vd for some drugs can vary fivefold or more between different individuals, and the results also depend on when the drug was administered. So the technique is approximate, at best, even in the living. But Derrick Pounder at the University of Dundee, UK, another member of the committee, says the method fails completely in a dead body. "There is an assumption on the part of some people that a corpse is a frozen living person," he says. "But drug levels don't remain static after death."
As cells die off they release the drug back into the bloodstream, so the concentration can shoot up 10 times, says Pounder. He published a paper in 1990 demonstrating this effect, but some expert witnesses are still testifying in court that they can work out the dose a victim took from post-mortem measurements. Goldberger says the problem is that doctors without forensic experience are applying the formula blindly. "People are acting outside their field, it is junk science," he says.
Karch has testified in American, British and Australian court cases and believes the mistake is becoming more widespread. He says around a third of cases where the technique has been used to evaluate drug levels involve fatal workplace accidents. Companies may try to shift the blame onto the employee by claiming they were under the influence of drugs when the accident happened. But what if a conviction largely rested on this formula? In 2001, an Arizona court found Brian Eftenoff guilty of murdering his wife, Judi. The forensic expert for the prosecution claimed that high levels of cocaine in Judi Eftenoff's blood indicated she died of an overdose administered by him. "I think that was a horrific miscarriage of justice," says Karch. In his testimony for the defence, he argued that it was impossible to say from post-mortem measurements whether she had even died of an overdose, let alone at the hands of her husband. We need to get this information out there, he says. "People are going to jail."
James Randerson, Dallas
New Scientist issue: 13 March 2004
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