Friday, November 16, 2007

Drug Testing Misunderstood


by blogger jgl

This case really irks me. First off, I'll be the first to admit that mistakes can be made in labs and it is entirely possible for false positives to occur. I will feel extremely bad for this guy if it turns out the lab made a mistake. However, if a mistake does occur, "proving your innocence" through shoddy forensic science is not the right path to take. Pay attention, forensic scientists! This is a classic example of an inappropriate use of forensic science to sway public opinion.

A summary of the case is as follows: Bronco's tailback Travis Henry tested positive for THC (urine). He's "proves" his innocence by taking a lie detector test and having his hair tested for drugs.

Travis Henry has convinced coach Mike Shanahan he's not a pothead. Now he'll take his case to the NFL.

Shanahan said Henry passed a lie detector test and a recent hair sample taken from Henry came back negative for marijuana.

"If the tests were positive, Travis would not be on our football team right now," Shanahan said. "When he went back and took the hair sample and that was negative, the lie detector test and that was negative, we'll let due process take care of itself. If Travis took a test and it was positive, after what he promised me, he wouldn't be on the football team right now."

Mainly because of his attempts to prove his innocence using *science*, his coach and TV personalities (including ESPN's Michael Wilbon and Dan LeBatard) are convinced he is likely telling the truth. I don't expect these guys to know anything about drug testing, but here are the facts:

Lie detectors DO NOT WORK.
Drug testing of hair DOES NOT WORK (for the most part).

Even if hair testing did work all the time, his hair is awfully short (grown in since the last drug test). By taking these bogus tests that scientifically prove nothing, Travis Henry has tricked educated people into jumping on his bandwagon. This demonstrates something most forensic scientists know, *the public often perceives anything scientific as infallible, but can't differentiate between "good" and "bad" science.*

If he really wanted to proclaim his innocence, then he should request that the lab retest his original sample. I don't work in a workplace drug testing lab, but don't they save a portion of samples for some length of time afterwards? Is Henry claiming his sample was mixed up with someone else's? How likely is this? Oh wait, it looks like the lab does have another sample that's already been tested according to this article.

But in a battle that has reached the federal court system, Henry is attempting to block the league from testing the so-called "B-sample" necessary to confirm the positive test, claiming that NFL officials would not allow his expert to be present for the testing of his specimen.

Something doesn't smell right. Plus, I hate to use a non-scientific fact to prove a point, but Henry has tested positive for drugs before (in 2005).

14 comments:

Anonymous said...

Alright, here's what I've been given for information. Urinalysis is very unexact. Reliability and validity ratings arundthe 60% mark. DNA hair testing-90+% on both. I see you're saying something entirely different. Where is a good reference for these statistics?

Anonymous said...

This case is ridiculous and should have been over with back in 2005. I can not call him guilty of using drugs but history is proof that he has used drugs before so it easy for the N.F.L. to point fingers at him. I mean Henry reversed the issue at hand and point fingers at the league for not allowing his expert to be present while he took the urine test. When the test came out positive and Henry stated that he was suing the league should have automatically ordered another test with the expert being present the second time around. A lie detector test???... are you serious... this guy is a professional athlete.. who is not to say he is not a professional liar as well. The lie detector test was a waste. As for the hair samples I do know the exact % of the accuracy of the testing but from what i have researched the results is really determined by the amount of the drug and consistancy of the drug being used. With the urine test i feel it would have been accurate because the urine is full of waste and horomones which is expelled out of the inner body so, it should be able to detect what ever toxin is in the body. TB

Anonymous said...

Travis Henry is not out to set the record straight. He is not suing the league for defamation. Travis Henry is hoping that the NFL will not call his bluff. I pose this question. Why did Henry not take the exact same test again after the results came back positive? It was Henry's decision to change the test method in order to prove his innocence. We can talk forensic statistics all day but research proves that the urinalysis is an effective means for testing traces of drug use. If urinalysis is an inaccurate testing method then why do several organizations beyond the NFL continue to use this method. I'll tell you why...because it's credible. -C.G.

Anonymous said...

This is very interesting to me. First off, why wasn't it mandated that Henry take another urine sample instead of the lie detector and hair analysis? This article has raised a few questions in my mind. How long does marijuana stay in the hair follicles? Well, I researched some articles and found that it is usually 90 days. Some articles also stated that body hair could also be used. Since body hair grows at a slower rate, how long could drugs be detected that way? What was the time peroid between the time he failed the urine test and the time he took the hair analysis? I tried to research this, but I couldn't find anything.I found this to be interesting though, "The NFL, sources said, is contending the rules are clear players can have their own expert present for testing, but the expert cannot be affiliated with a lab or testing service and Henry's expert was affiliated with a lab". (Rocky Mountain News)

UAB MSFS Program said...

great comments.

I believe the first comment is from a non-student and I wish i would have had the time to fully respond earlier. I wanted to find some more sources, but i'll give you what i got.

For urinalysis testing, i'm not sure where the 60% stat comes from, but it is believable. My guess is that the "low" number comes from the fact that some drugs can be in a low concentration in the urine, and are eliminated fairly quickly, depending on the drug and the original amount taken (72 hours ballpark). In this case, all indications are that it was a recent, one time consumption of marijuana that was detected. Urinalysis is good for that.

FOr 90% hair, you mention DNA, which is a different test than drugs in hair, so the 90% could be correct for DNA, but wrong for hair. Or, as with any stats, one guy could have done a test where the conditions favored detection and recovered drugs in 90%. In my quick search, I couldn't find any articles focusing on detecting short term use in hair. All hair articles focus on detection of drugs in chronic users [one example - Skopp, et al. Forensic Sci International 170 (2007)]. This supports the conventional wisdom that hair analysis isn;t good for recent, one-time use.

as for the lie detector, the most comprehensive study on the technique concluded it was junk science (National Research Council "The polygraph and lie detection", 2003). it is. It disgusts me that it is still portrayed in the media (and tv talk shows) as legitimate.

finally, for the last comment, taking another urine test seems like the right thing to do, but after the first positive, surely the THC was out of his system, unless he was a complete idiot and continued its use. And i think he 90 day stat is for chronic users.

finally, with all the criticism of his "legal" actions i would like to state that Henry isn't necessarily a bad guy. I'm sure he's not the first guy to use marijuana near the end (or during) a season. That's fine, but to make the big bucks, you have to play by the rules.

dr. L

Anonymous said...

Hair analysis for substances of abuse is not nearly accurate enough to be used. see http://hairanalysistesting.blogspot.com

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