A well-known singer used hair testing to prove his innocence. Why is hair testing called the "magic mirror" for drug-related personnel?

Drug use is illegal in our country, but when it comes to suspected drug users, solid evidence is still needed to impose corresponding punishment on them. Therefore, public security organs usually adopt some scientific methods to conduct testing. The most common method is urine testing, which is easy to operate, fast, and not restricted by venue.

As the name suggests, urine testing is to test the urine components of the suspect. If the sample contains drug precursors and their metabolites, it will combine with the antibodies fixed on the test paper to form an antigen-antibody complex, and then combine with the antibodies in the quality control area (C line area) to produce a purple-red reaction, that is, a positive result with a purple-red line.

Although urine testing is simple and convenient, it has some obvious flaws, such as the short validity period of test samples (three to seven days), samples are easily contaminated by other substances, and suspects can accelerate metabolism and excrete drug precursors and their metabolites from the body by taking auxiliary drugs, which can lead to deviations in results or even make the test impossible.

Similar detection methods include saliva testing, sweat testing, etc. The operations are similar. They all detect metabolites in human body fluids. Since the principles are the same, the defects are also the same. The test samples are short-lived and the collected samples are more easily contaminated by other substances that enter the mouth.

Due to the defects of urine and saliva tests, as well as the limited types of drugs they can detect, public security organs sometimes use more accurate blood tests. The principle is the same as that of drunk driving blood tests, that is, the suspect's blood is tested and analyzed to confirm whether it contains drug antigens and their metabolites.

Although the results of blood tests are very accurate, they require a higher timeliness of the sample (24 to 48 hours), because the metabolism of blood is very fast, and the drug precursors and their metabolites are easily metabolized. In addition, due to the high cost of blood testing equipment, only a few provincial hospitals or laboratories are equipped with it, so it is not suitable for widespread application.

In summary, we can see that whether it is urine testing, saliva testing, or blood testing, it can only detect whether the suspect has taken drugs recently (up to 7 days). Once he stops taking drugs one week in advance, or takes auxiliary drugs to speed up the body's metabolism, the test will become meaningless.

So, is there a method that can detect drug use for a longer period of time? The answer is yes. It is a high-frequency word that has appeared in news reports on celebrity drug use in recent years - hair testing. It is a technical means that has the characteristics of urine testing, such as convenient and fast operation and easy sample collection, as well as the accuracy of blood testing and the ability to detect more types of drugs.

Hair testing originated in the 1970s, and the technology is mature and stable. In 2016, my country's Ministry of Public Security revised Article 6 of the "Regulations on Drug Testing Procedures" to "test samples are biological samples such as urine, blood, saliva or hair collected from the person being tested", giving hair testing a legal status in drug law enforcement.

Compared with urine testing, saliva testing and blood testing, hair testing has incomparable unique advantages, such as comprehensive information on drug precursors and their metabolites, easy sample collection and preservation, and effective prevention of suspected drug users from falsifying evidence. Most importantly, the drug use traceability period is longer.

Why can hair testing have a longer traceability period for drug use? The main reason is that drug precursors and their metabolites enter the hair follicles through the blood circulation, are fixed by the keratin in the hair, are stored stably for a long time, and migrate continuously from the hair roots to the hair ends as the hair grows.

The preservation time of drug precursors and their metabolites in hair, that is, the validity period of sample testing, depends on the length of the hair of the person being tested and the differences in metabolic generations. In theory, the drug abuse tracing period can be as long as several years (as long as the hair is long enough), but in practice it is generally within six months.

It is worth mentioning that the samples for hair testing are not limited to head hair. Other body hair such as leg hair, pubic hair, and armpit hair can also be used. Therefore, even if the person being tested is born bald or wants to avoid testing by shaving his head, other body hair samples can still be used for testing.

In addition, hair dyeing will not affect the results of hair testing. As for the reason, you need to first understand the two methods of hair testing: on-site (rapid) testing and laboratory (precise) testing. The former has relatively simple equipment, fast analysis speed, relatively general sensitivity and accuracy, and is usually only used for rapid initial screening.

The laboratory generally uses liquid chromatography-mass spectrometry for precise detection, which is expensive but highly sensitive and accurate. According to the actual operation of the National Drug Laboratory, the original drug and its metabolites can be detected in dyed hair.

It is also worth mentioning that precise laboratory testing can also use comprehensive information about the drug precursors and their metabolites in the sample to compare the content (for details, see Article 9 of the "Specifications for Hair Sample Testing of Drug-Related Personnel" published below) to rule out false positives caused by taking related drugs or sample contamination.

"The detection threshold for O6-monoacetylmorphine (heroin), morphine, methamphetamine (ice), amphetamine, 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA ecstasy), ketamine (K powder), norketamine, and methcathinone in hair samples is 0.2 ng/mg; the detection threshold for cocaine is 0.5 ng/mg; the detection threshold for benzoylecgonine and tetrahydrocannabinol is 0.05 ng/mg. If the actual detection content value is above the threshold, the test result is considered positive."

At present, due to the high cost of equipment, precise hair laboratory testing is not widely used. Most grassroots public security organs often use urine testing and on-site rapid hair testing. Only when the suspect disagrees with the test results or suspects that the test time limit has been exceeded, will they entrust the identification agency to carry out precise hair laboratory testing.

References:

Song Mia. Hair testing: making hidden drug users nowhere to hide. China Anti-Drug News, September 11, 2018, Page 004

Ministry of Public Security "Specifications for Hair Sample Testing of Drug-Related Personnel"

Ministry of Public Security's "Drug Testing Procedures"