Current Affairs Journal: Fifth Entry

If you take a closer look at science fiction TV shows, you will realize that the ways forensic processes or technologies are represented vary greatly. Some shows manage to represent forensic processes very accurately. Still, there are shows that paint a picture that creates completely unrealistic ideas and expectations about this field of work.
As an example, I would like to look into a scene from the BBC’s TV series “Sherlock”. In the last episode of the third season there is a scene which shows Sherlock’s urine being tested for drugs. The scene itself is very short and only consists of three short sequences: the urine sample being taken out of a cup, the sample being mixed with a chemical substance and it being analysed under a microscope. But can urine actually be tested for drugs like this? Is this actually possible or just something the writers of “Sherlock” came up with?

In order to detect illegal substances in any body fluid (let’s assume it is urine), two certain tests are performed: a presumptive test and a confirmatory test. The first type, the presumptive type, can be performed on-site already but it is usually performed in the laboratory. The aim of presumptive tests is to tell if there are any drugs in the questioned sample. Those tests only result in positive or negative results, though. They are unable to identify the specific drug that was found but only the class of drugs it should belong to. In addition, presumptive tests don’t always give clear results or results that can be misinterpreted which makes them unreliable. Only a confirmatory test is able to tell specifically what it is that was found in the sample. Usually the whole process of toxicology screening (examining the patient, presumptive & confirmatory analysis, comparing,…)usually takes between four and six weeks.

The many different types of presumptive tests span from ultraviolet spectrophotometry and microcrystalline tests to Colorimetric tests. Certain reagents in these colorimetric tests react with chemical components of the different drugs. A testing kit for a colorimetric test consists of a specialized paper that changes its colour when it gets in contact with a certain substance. If it turns one colour, the drug is present in the sample. If it turns another, it isn't. The colour it changes to varies because every drug causes a different chemical reaction.  Ultraviolet spectrophotometry is another procedure where the sample is treated with ultraviolet light and, according to the sample’s reaction, analysed and categorized.

Confirmatory Tests are performed either via Gas Chromatography/Mass Spectrometry (GC/MS) or just via Gas Chromatography or Mass Spectrometry. Each of these three processes tries to find out the substance’s chemical signature. The Mass Spectrometer vaporises the atoms that are analysed before they are turned into positive ions (by knocking out electrons). These ions are then accelerated, so they turn into beams, and deflected by a magnet. It depends on their masses on how strongly the ions are deflected e.g. a golf ball would be deflected more strongly than a snooker ball. The beams hit a detection plate and create a tiny electrical current. The more ions of a specific mass-to-charge-ratio, the greater the electrical current and the bigger the graph in the stick diagram becomes. 

The Gas Chromatography on the other hand works in a very different way. A vaporized sample is carried through a “column”. For the sample to be carried through the column (which looks more like a tube, really) you need a gas like nitrogen. The atoms in the sample are carried through the column at different speeds, which is why they separate. A detector then detects the different chemicals and are shown as peaks on a chart. The succession of the difference substances on the chart tells you what chemical it might be. So the difference between MS and GC is the following: while GC only tells you what it is that’s in the chemical, MS can tell you the masses and charges of the substances. This is the reason why those two types of confirmatory test are most often combined to a GC/MS test.

Now, if we look at the scene again (and look at footage that doesn’t show the drug testing) you can see a rather dazed and seemingly tired Sherlock. As a viewer of the show, the audience knows that Sherlock was addicted to heroin. This leads to the presumption that Sherlock might be high on heroin. If a forensic scientist would look at this situation, he or she would usually take an additional step before presumptive and confirmatory testing: analysing the behaviour of the person that has supposedly consumed drugs. Heroin causes a person to be "drowsy" which is why, if one were to observe Sherlock in the scene, his behaviour is accurate.

Now if you look at the scene again, you’ll notice that the three steps I mentioned above (“taking the sample, mixing it with chemical, analysing it under the microscope) don’t fit any of the above mentioned tests. But then again…I mentioned something about a microcrystalline test which I intentionally left unexplained. This test, also a presumptive test, consists of three simple steps. A chemical is put on a slide and mixed with a drop of the sample. The reaction of the substance with the chemical leads to the forming of crystals. The form of the crystals differs very much, though, because every drug has a different crystal pattern. The crystals are then analysed under a light microscope and according to those you can at least identify what class (e.g.narcotics, stimulants,..) the drug belongs to.

So the answer to this overly long post is….yes, the procedure shown in the episode of “Sherlock” is, or could, actually be a real forensic procedure. Well then, kudos to Mark Gatiss and Steven Moffat.