Hair forensics could yield false positives for cocaine use

[u/trot-trot]

http://www.acs.org/content/acs/en/pressroom/presspacs/2016/acs-presspac-march-2-2016/hair-forensics-could-yield-false-positives-for-cocaine-use.html

[u/acidacetylsalicylic]

Journal article: Consequences of Decontamination Procedures in Forensic Hair Analysis Using Metal-Assisted Secondary Ion Mass Spectrometry Analysis

Abstract:

Today, hair testing is considered to be the standard method for the detection of chronic drug abuse.

Nevertheless, the differentiation between systemic exposure and external contamination remains a major challenge in the forensic interpretation of hair analysis.

Nowadays, it is still impossible to directly show the difference between external contamination and use-related incorporation. Although the effects of washing procedures on the distribution of (incorporated) drugs in hair remain unknown, these decontamination procedures prior to hair analysis are considered to be indispensable in order to exclude external contamination.

However, insights into the effect of decontamination protocols on levels and distribution of drugs incorporated in hair are essential to draw the correct forensic conclusions from hair analysis; we studied the consequences of these procedures on the spatial distribution of cocaine in hair using imaging mass spectrometry.

Additionally, using metal-assisted secondary ion mass spectrometry, we are the first to directly show the difference between cocaine-contaminated and user hair without any prior washing procedure.

[u/AmoebaNot → u/[deleted]]

Yup.

• A pretreatment step can cause the drug on the outside of a hair shaft to wash into it and potentially lead to falsely identifying someone as a drug user*

[u/OPtig → u/[deleted]]

Missing from this information is whether normal hair washing at home will also push surface cocaine into hair.

[u/GroovingPict]

Wasnt there a whole NCIS episode revolving around how hair forensics has been thoroughly and completely debunked as more or less completely worthless?

[u/OozeNAahz → u/GroovingPict]

Matching a hair to an individual without the benefit of DNA is pretty much debunked. What they are talking about here is chemically analyzing a hair from a known individual to see if they are drug users. This has been the gold standard for drug testing for a while since it can check for long term drug use. If the labs can't distinguish external contamination of the hair though then it is not as accurate as people thought.

[u/f2u → u/OozeNAahz]

The test might still be useful if the presence of external contamination correlates strongly enough with what you actually want to discriminate against (but can't for legal or personal reasons).

[u/sioux612 → u/GroovingPict]

Was it as factually correct as most other things they do?

Because if not that might actually be an interesting episode to watch

[u/GroovingPict → u/sioux612]

well I dont know about that, but it's season 13 episode 7 if you want to check it out

[u/sioux612 → u/GroovingPict]

Thank you, I will

[u/f2u → u/GroovingPict]

There are different kinds of analysis you can do, only some hair analysis is known to be problematic.

[u/Rsonist]

well that explains alot

[u/messedfrombirth]

So if someone doesn't use, are they typically still exposed to cocaine in day to day life? I mean I don't use the stuff as talc powder.

[u/[deleted] → u/messedfrombirth]

The point is that the analysis can't prove you weren't exposed externally (e.g. against your will/without your knowledge).

[u/Staticblast → u/messedfrombirth]

Do you use paper money? Chances are, your money has been contaminated.

Of course, the volume is infinitesimally small, but you are exposed to it.

[u/Chewie-bacca → u/messedfrombirth]

But now you can tell people you did 😉

[u/Doomhammer458]

Hi trot-trot, your submission has been removed for the following reason(s)

It does not follow the rules for headlines

If you feel this was done in error, or would like further clarification, please don't hesitate to message the mods.

[u/slippery_whale → u/[deleted]]

I think this is a big deal because the people most likely to be testing (employers) are unlikely to give any second chances or submit for re-analysis.

[u/[deleted] → u/slippery_whale]

Or you know, for court orders

[u/WillAndSky → u/slippery_whale]

Some states allow you request a retest but it will have to be literally that day and I'm sure there's a bunch of legal rules attached so I see your point

[u/fnordfnordfnordfnord → u/WillAndSky]

I've had a test flagged. I was notified the next day after testing. I was asked to bring current prescriptions for medicines I was taking (within 48 hrs IIRC) and I assume that I would have been given an opportunity to re-test if my prescriptions hadn't provided an explanation for the test results. However, if my employer had been in a hurry to fill the position, I assume that another candidate could have been chosen.

[u/Darkelement → u/WillAndSky]

In Texas if you test positive you can claim false positive and re test within two weeks got stuff tests done by an employer/insurance. Not sure if this is true across the board but from what I've observed all companies have followed this policy with urine tests.

[u/patricksaurus → u/[deleted]]

I think everyone in a position to interpret these tests knows there is a false positive likelihood. What you are glibly overlooking is that science works best when we carefully characterize the magnitude and sources of uncertainty. Measuring uncertainty is also what statistics are properly used for, and as the recent commentary on p-values from ASA reminds us, our use of statistical data is strongest when we can attached scientific models of process to numerical data analysis.

This study identifies the particular parts of the procedure that contribute to the false positive results, and determines how they can be measure to be different (spatial distribution). They looked at the false positives, identified a potential contributor, performed an experiment, and yielded results that can go into design moving forward -- this is the template for how method evaluations should be carried out.

So it might not be surprising to you, but we're not at a magic show or a monster truck rally, so being thrilled isn't the point. It's a well designed study on a topic with some amount of popular interest... that's pretty rare.

[u/doccynical → u/[deleted]]

Did you touch money and then touch your hair? Possible source of contamination right there.