The Toxpod

The TOXINvestigator

January 02, 2019 Season 1 Episode 7
The Toxpod
The TOXINvestigator
Chapters
The Toxpod
The TOXINvestigator
Jan 02, 2019 Season 1 Episode 7
Tim Scott & Peter Stockham
Tim ponders the role of the Forensic Toxicologist as an Investigator
Show Notes Transcript

What is the place of investigative work in forensic toxicology? Should the forensic toxicologist take the same approach in every case? Or should they use their judgement to decide on the best approach for each unique case? Either way, there are a lot of complex issues that arise. Luckily, Tim has all the answers! (or at least some of the questions...)


Contact us at thetoxpod@sa.gov.au


The Toxpod is a production of Forensic Science SA and the South Australian Attorney General's Department. The opinions expressed by the hosts are their own and do not necessarily reflect the views of their employer. 

Tim:
0:11
Hello and welcome to The Toxpod. I'm Tim Scott and flying solo today, Pete couldn't join me. So I want to talk about a topic that that I've been considering for the last few years, I suppose. In fact this episode is kind of a mixture of a few different articles and presentations that I've done looking at this topic, and here's the question: Is the role of a forensic toxicologist to be an investigator? Or should they just be providing the results that they've been asked to give? Now you might say, well, of course they should be an investigator, that's a key part of their job, but there are a lot of things which really push back against that idea and there's a lot of complexities once you start getting into the detail of what that really means. And so I want to explore some of those things today.:
Tim:
0:56
We've mentioned a few times on The Toxpod in various episodes about comprehensive screening methods and that's really where a lot of forensic laboratories are trying to get to, having a very large method that looks for hundreds of different compounds. But along with that goes the idea of untargeted screening, looking for things that you haven't preselected, just seeing what shows up in the screen. Obviously this type of targeted screening only works if you're using full scan techniques, that might be full scan LC/MS or GC/MS or LC/UV or another type of full scan technique, and this is a really important part of providing a good forensic toxicology service. And I've come across cases in my career where perhaps you're investigating a death, there's no obvious medical cause of death, no obvious suicide, standard targeted drug screening is negative, but then an untargeted screen shows up an unusual drug that you probably wouldn't have looked for otherwise. Maybe it's a pesticide or a poison that's not in your normal screening regime. Maybe it's an NPS that you haven't seen before or that you didn't know was available in your area.:
Tim:
2:06
And it's not just about determining cause of death, this kind of thing also happens when you're trying to work out if someone was impaired while driving or in a range of different circumstances. The number of times when a client, say a police officer, will bring in some item, it might be a blood or a urine sample, or it might be some food or beverage or something else that they found at a scene and they'll say, we think this might have been poisoned. Can you test it? And I'll say, sure, what would you like me to test it for? And they'll invariably say, well, you're the expert, you tell us what you should be testing it for! It's kind of like someone taking their car into the mechanic and saying something's wrong with my car and the mechanic says, okay, what seems to be the problem? I don't know, you work it out! Where do you even start in that circumstance?:
Tim:
2:52
So having broad screening methods is really important as a starting place for this kind of work, but then often you're going to need rely also on untargeted techniques and what you then need are generic extraction techniques, full scan instruments. But the problem with doing this is that you're going to find a lot of different compounds and the idea of reporting every compound that you see, that you find, that you identify, it's not just impractical, it's impossible. Imagine a total ion chromatogram from a GC/MS. You've probably got hundreds of visible peaks in the total ion chromatogram, and if you were to start extracting out individual ions, you'd have even more peaks. Each one representing a different compound. There's no way to report all of that. So what, you might say, you don't need to report all of it. Most of those compounds are going to be endogenous or irrelevant. Just report the things that are significant, and this is where the real issue lies. This is the real question, how does the toxicologist know what is significant and what isn't significant in any particular case? And it's not like you can set up your methods to only detect things that will be significant. I mean, wouldn't it be nice if the potency of a drug was directly proportional to its sensitivity in analytical methods, but it's just not.:
Tim:
4:08
For instance, you might be screening acidic drugs using LC/UV and perhaps in your method you've got some barbiturates and you've also got some anti-inflammatories. Well, a drug like naproxen is going to be very sensitive in that method just because it's so responsive by LC/UV because of that naphthalene backbone, whereas something like pentobarbitone is going to be a lot less sensitive even though it's really a more important drug to be detecting in most cases. It's not that you're trying to detect very low concentrations of naproxen, but you will because when you're developing a method, you tend to focus on the least sensitive drugs in that method, they're really your priority because you need to be able to get down to therapeutic levels or maybe below sometimes, but that means that other drugs which are just inherently more sensitive by whatever technique you're using, you're going to detect them at tiny concentrations, like with naproxen in the example I just gave. Should you report that tiny level of naproxen? Maybe you think it's insignificant, but how do you know and where's the line when something becomes significant? Often to report a drug, laboratories will need to do some further work, perhaps reanalyzing the sample, perhaps even by a different method, and this consumes precious resources and seems like a complete waste of time for what will almost certainly be an insignificant concentration of a drug. Resources that could be much better spent on improving turnaround times or following up more complex cases or developing new methods that are going to improve your scope of analysis. Things that will be of much greater benefit to your laboratory and your clients both now and in the future.:
Tim:
5:50
So where's the balance? At one extreme, you could report everything that you detect. On the other extreme, you could decide what to report on a completely case by case basis and really there's a broad spectrum of views in between these two extremes and different laboratories take different approaches and have different policies and are working in different environments as well. So let's take a look at some of the things that influence where you might sit on this spectrum and what are some of the consequences that come out of that. Now, for some applications it's really simple because it's governed by legislation, so for example, drugs and driving work in a lot of jurisdictions, it's governed by specific legislation. There are certain drugs you need to screen for and you don't need to screen for anything else. In fact, in many cases you're not allowed to screen for anything else, so there's no thought at all needed there. That decision's already been made in the legislation as to what you're going to look for and what you're going to report. Or sometimes there are standards that govern certain types of testing, international standards or regional standards for things like workplace testing, whether that's oral fluid or urine or hair, so if you're accredited to a particular standard, that also makes it pretty easy because you're just going to comply with whatever is in that standard. Although some standards are a bit broader than others and allow for some discretion by the laboratory in terms of what to report. There are some guidelines as well for forensic testing. The Society of forensic toxicologists in the US has put out some guidelines about toxicology testing and drug facilitated sexual assaults, which drugs you should be looking, for what kind of levels you need to detect -minimum detection limits, that is. Because some of the relevant drugs are at quite low concentrations in blood or urine. But those guidelines aren't comprehensive and they don't necessarily apply to every case equally. It can get very complicated.:
Tim:
7:40
For example, consider this idea of irrelevant compounds. I was saying before about how many hundreds of compounds you might see if you're doing an untargeted screen and I think all forensic toxicologist would agree that there are some compounds that are always irrelevant and you don't ever need to report them, like cholesterol for example. Now that's important in some clinical testing, you might be specifically looking for that, but in forensic testing that's not a significant compound. But you'll tend to find it if you're doing a full scan GC/MS screen for example, but it's completely irrelevant, right? It's not a drug as such and so it's not necessary to report it, but what about something like b-phenylethylamine. That's a product of decomposition, it's commonly found in postmortem blood samples. It's almost universally found in fact, but it can also be used as a drug, it's been promoted as an exercise supplement, so it might be something that a toxicology lab wants to have in their drug screen, but it's very difficult to know when you find it, whether it's endogenous or whether it's been used. In most cases it's going to be endogenous, but how do you know? Caffeine. Another almost universally found compound in biological samples. It's present in not just coffee, but a whole range of different foods and beverages, so most people have caffeine in their blood, but there've been many reported overdoses of caffeine, so it's a forensically significant drug and you really want to be looking for it, but when you find it in almost every case, should you report it in all those cases, do you need to quantify it in all those cases? Most of the time it's going to be an insignificant concentration, but sometimes it will be significant and you don't necessarily know whether it's going to be significant or not in a particular case. What about metabolites? A compound like quetiapine, an anti psychotic drug has a whole bunch of different metabolites. Most of them aren't active, they're not important in that sense, but you might have them in your method because you're doing urine screening and so you might not always be finding the parent drug, but then maybe you're using the same method to apply to blood screening as well, so you'll find these inactive metabolites in a blood sample along with the parent drug. Should you report them? You might also have inactive metabolites in your method if you're using a full scan method because you know that they're going to show up as large peaks in the total ion chromatogram or base peak chromatogram and you don't want to spend any time investigating them, oh, what's that peak? I better go and have a look at that. You want to be able to rule them out immediately and dismiss them because as I mentioned, following these things up often requires more work, another extraction, a re-injection, confirming by a second technique, etc. Different jurisdictions have different guidelines about these sorts of things. You don't want to report them, but you've detected them, so how do you make that decision about what to report and what not to report.:
Tim:
10:30
So there's that concept of irrelevant compounds, but what about insignificant concentrations? I gave that example about naproxen before on an LCUV, you don't really want to detect such low concentrations, but sometimes you can't help it. You're limit of detection is just too good for some drugs! You might have a case where someone's found deceased in their car, in the garage, they've got a high carbon monoxide level and also a tiny amount of paracetamol, say one milligram per litre. Is it necessary to report that? Or again, talking about metabolites. What about active metabolites that are also drugs themselves but are clearly present in the case as the metabolite? So for example, codeine is metabolized to both hydrocodone and dihydrocodeine, which are both drugs in their own right. If you find a high level of codeine in a urine sample, you may find small amounts of both hydrocodone and dihydrocodeine. Do they need to be reported? They pretty clearly just metabolites of the codeine. It's the same situation with decomposition products. We've talked about that on a previous episode too, but for something like methamphetamine, when its smoked, it produces a small amount of dimethylamphetamine, which is also a drug. Or dimethylamphetamine might even be in the the meth powder as a byproduct of synthesis, so you may detect it at very small concentrations when you find a high level of meth. Does it need to be followed up and reported?:
Tim:
11:57
What about other impurities? Amitriptyline, for example, a very widely used antidepressant now actually used a lot to treat neuropathic pain. It has a known impurity, cyclobenzaprine, which is also a drug, a muscle relaxant, very similar structurally to amytriptyline, its just one carbon carbon double bond that's the difference, and it's a known impurity in amitriptyline formulations. It's only in very small amounts, but again, if you're screening urine, the concentrations of amitriptyline might be quite high and chances are you'll find a small amount of cyclobenzaprine. Does it need to be investigated and reported? It takes time to pursue all these things which are almost certainly irrelevant to the case.:
Tim:
12:40
Or, think about a technique where you're trying to detect not just a single compound, but a profile of compounds. Something like volatile hydrocarbons. If you're testing say a lung sample for the presence of petrol, you're not looking for one particular compound, you're looking for a range of aliphatic and aromatic hydrocarbons and it's the total profile that you're looking for. Generally, you don't want to report these compounds individually. What you want to be able to say is something like compounds consistent with petrol were detected in the lung. But what if you only detect some of these compounds? Should you report the presence of the individual compounds? They don't necessarily come from petrol, they could have come from the products of combustion of household materials if there was a fire. We know that things like toluene, xylene, other substituted benzenes are produced in fires. In that instance reporting the presence of these compounds might be misleading. It could lead investigators to think that petrol was somehow involved when it really wasn't.:
Tim:
13:38
What about hair analysis? We've talked about that in a previous episode too. The society of hair testing specifies cutoff concentrations to detect chronic drug use, mainly for use in workplace testing type situations because very low concentrations of drugs in hair can be misleading in that type of situation. Reporting a low concentration of a drug like methamphetamine or cocaine or THC may lead people to think that the person has taken that drug recently, but it doesn't always mean that, but when you're testing hair in a drug facilitated crime scenario, you'll want to look for those very low concentrations and the society of head testing guidelines do recommend lower cut offs in those type of cases. But that's where it gets very tricky because: What is drug facilitated crime? Obviously a case where someone has had their drink spiked and then been sexually assaulted, that's a drug facilitated crime and so you'll want to use those lower cutoffs to find that single dose of drug that they've been given. But what about if you're testing the hair of someone who accidentally injured another person in the workplace? It's possible that they will be charged with a crime at some point. That's not up to the toxicologist to decide that, but the toxicologist does have to decide which cutoffs to use for their hair test. What about if you're testing the hair of a child who may have been exposed to drugs in the family home? Is that drug facilitated crime? What about if you're testing the hair of their parent? Is that drug facilitated crime? And I could go on and on about all sorts of complex situations where it's very difficult to know what kind of reporting limits are appropriate in each case because the toxicologists isn't always aware, in fact, they're almost certainly not aware of all the issues in any case.:
Tim:
15:27
And there's a lot of practical issues here as well. Where are the decisions made? If a decision's made by the analyst in the lab not to follow up a particular peak in a chromatogram, the reporting scientist might not even ever see that. Many people might say that the scientist shouldn't be making any decisions about what to report and not to report. They should just report everything and let the courts sort it out, but you've got to be careful what you wish for. That seems like a very simple thing on the surface. Just report what you find. But as every toxicologist who's ever interrogated a full scan mass spec chromatogram knows, what that would lead to is massive toxicology reports full of mostly irrelevant compounds which clients would find impossible to decipher. What am I supposed to be looking at on this report that's significant. But actually in practice, what it would more likely lead to is that tox labs would just shrink the scope of their analysis. No more unknown screening because you don't want to find a hundred irrelevant compounds that you then have to follow up and report. You don't have the resources to do that. So instead you just do targeted analysis on the drugs that you know you have the resources to follow up. Is that really a better situation? Does that really provide a better service to your clients? You'll never see anything except what you're specifically looking for. And that's obviously safer for the toxicologist. It protects them from criticism because they're not making any of those difficult decisions themselves, but safer doesn't mean better because it would be nowhere near as informative and it really relies on information then from other investigators to know what compounds to target rather than the toxicologist herself being part of the investigative chain.:
Tim:
17:11
On the other extreme, you could report everything on a case by case basis and what that would lead to is inconsistent reporting, it's open to criticism from others and fair enough, the toxicologist doesn't have all the information about the case. Who are they to be making those judgements? And that's a reasonable criticism to make even though they have expertise about the pharmacological effects and the potential sources of different drugs and compounds. Is the compound just a metabolite of another drug? Is the compound just an impurity of another drug? Is the compound just a degradation product of another drug and so it's not going to be important? Assuming the parent drug itself is reported. Is the concentration of the compound forensically insignificant, whatever that means, I'm doing air quotes here which you can't see, but you can debate that term forensically insignificant because it's not completely clear, even two toxicologists may disagree about that. I would argue that no one else in the investigative chain is better qualified to make those decisions than the toxicologist, but they're still basing those decisions on limited information about the case. But the crucial advantage in taking a case by case approach is that you can find the unknown. You can spend the time investigating what's there, turning over every rock in that full scan chromatogram because you know you're not going to have to follow up every single compound that you detect, you're going to have the freedom to investigate.:
Tim:
18:39
So it's very difficult to find the balance here. I think probably both of those extremes should be avoided, but there are some things that you can do to try and find that balance. You can have recommended limits of reporting. Not strict limits of reporting like a cut off concentration that you might find in a standard, for example, but recommendations to your scientists that concentrations below a particular cut off are probably not necessary to report in the majority of cases. I mean is it really necessary to report that paracetamol concentration of less than one or two milligrams per litre? In most cases no, it's not. Especially if you're talking about postmortem toxicology, and you can take an approach like that for a whole range of drugs where the therapeutic concentration range is well known and the limit of detection for your method is well below that, but that's not to say that there won't be a unique case at some point where that drug will be significant and it should be reported at a tiny concentration. Having a strict cutoff across all cases might mean that in that one unique case, there's important information that you're not going to provide to the investigators. You might even have different guidelines for different types of cases, coronial cases, criminal cases, driving under the influence. They all have different requirements and different cutoffs might be appropriate for each of them, but they can't be rigid guidelines.:
Tim:
20:07
Screening for unknowns can be problematic because what do they teach you in your first toxicology lecture, that old quote from Paracelsus, any compound can be a poison, it's the dose that matters, so when you're looking at that untargeted screen and seeing a whole bunch of compounds that in the right dose could be poisons, but are almost certainly not. You've got to use your experience and your judgment to decide what needs to be followed up. I think really the main thing that the toxicologist needs to focus on is this, what question is being asked by the client? So that police officer who comes in says, hey, can you test this for me? The question to ask is not what would you like me to test for, but what question are you trying to answer? Because they don't necessarily even know what tests to ask for let alone what compounds should be reported based on those tests, but what question is being asked? Are you trying to determine a cause of death? Are you trying to tell if someone was under the influence of drugs when they committed a crime or when they had a crime committed upon them? Are you trying to tell if a child has been exposed to drugs? Are you trying to tell if someone's dinner has been spiked with a poison or if someone's drink has been spiked with a sedative? What question is being asked? Obviously you need to consider any relevant legislation, standards, guidelines, all of that is very important, but as I said, these don't always apply and they're not always relevant.:
Tim:
21:39
You need to consider the resources of your laboratory. That's a real issue. You can't do more work than you have resources for. That's just reality, but the toxicologist has to be free to some extent to use their expertise to pursue leads. Just like a police investigator pursues leads in the way that they know how, a toxicologist pursues these chemical leads in the way that they know how, in the way that they are uniquely qualified to do. We need to strive to find that balance between either extreme, either having to mandatorily report every compound detected or on the other hand, deciding in each case what to report and what not to. That balance is really difficult to find and I'm not suggesting that I have all the answers to finding that balance, but we need to keep striving to find it because the toxicologist is a crucial part of the investigative chain, is an investigator in their own right and can't ever settle for just taking the same approach in every single case. That's a second rate toxicology service. We've got to be better than that.:
Tim:
22:46
So that's my thoughts on the toxicologist as an investigator. I'm sure there's lots more to say about that subject and you might even disagree with me about some points, but that's the whole point of this podcast, is to promote conversation within the field. So if you've got any comments or questions, email us at thetoxpod@sa.gov.au. Peter will be back on board for the next episode. Thanks for listening and we'll see you next time.:
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