The Stat Lab


On the internet I am known as Slip. I am a 22 year old nerdface who practically lives and breathes laboratory medicine.

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Lab Tests

Anonymous asked: Hi, I just had a swab for a job I'm up for. The test results were so wrong! It said I was positive for THC - IMPOSSIBLE! And it showed a negative for opioids - also IMPOSSIBLE, as I take percocet daily and hydrocodone approximately every couple weeks. What is up with this! I'm a bit upset about being so humiliated in the presence of my potential employer with these false results, and could lose my opportunity for employment. Please respond as soon as you can. Thanks, Maria

Hello Maria,

Unfortunately when it comes to immunoassay screens the reasons for a false positive or false negative are as numerous and diverse as there are companies that make them.

Specific to our region but may/may not be relevant to yours too: Percocet actually contains oxycodone which, while it is an opioid, is actually detected in a separate oxy- opiate screen, not the classical opioid screen.

Hydrocodone is also rapidly metabolized into hydromorphone and opioid screens are not very good at detecting hydromorphone. If it’s been more than a few days since your last dose, I would not be surprised by a negative result.

False positives are a whole other can of worms. It sounds like you have chronic pain and even common painkillers like advil/ibuprofen can give a false positive THC. The different families of drugs being screened for all have different performances and the medical review officer for the area will know best how to correlate the results with the medications you declare.

In either case, confirmatory testing will back up your claims so I wouldn’t worry too much. Trust me, your situation is definitely not a rare one! I used to get a lot of calls from seniors asking why their amphetamine screen was positive (good old vicks).

I hope that eases your fears a bit. Sorry if that was a bit wishy washy though. That’s just the nature of screening tests.

One of our biggest clients is the local psychiatric hospital because a good chunk of the facility is rehabilitation and addiction management. Lately, there’s been a population of patients who were coming up positive on the amphetamine drug screen but we have never been able to find anything that could explain it in the confirmations. This is not the most bizarre thing because amphetamines are very volatile so if you have a tiny concentration in the urine, you might lose it in the extraction (which contains dry down steps).

However! One day we got a box full of homemade cigarettes from the hospital which were taken from an “entrepreneur” who was selling them to patients and we were asked to do extractions on them to see if maybe we could find this mystery amphetamine or cross-reactant. (Unrelatedly, I thought the surgeon general’s warning sticker is a really charming touch)

We tried a number of extraction methods but never did find the amphet. In fact what surprised me was the fact that, compared to commercial cigarettes, these were actually really clean!

So I have an interesting case of environmental toxicology.

One of the local hospital’s neonatal ICUs has been suffering from an outbreak of bloody diarrhea. Obviously the first thing they suspected was some sort of infection, so they recruited an epidemiologist to puzzle it out, but they quickly ruled out both bacterial and viral infections.

We got a bunch of water samples from them for trace elements analysis and it came back negative. But we also got some baby bottles from them and they had really high zinc levels, so they suspected something is leaching from the bottles.

We then got a bunch of urine samples from the babies and indeed the zinc levels are through the roof.

We asked the clinical toxicologist if this could be related and indeed, high zinc levels can be a cause of bloody diarrhea. Imagine that.

When samples come into our lab and there is any possibility that they can turn into medical-legal issues (eg, impaired at work, related to a crime, but usually drug facilitated assault), we will not run them. In the case of assault, our toxicologist will phone the ordering doctor to tell them the sample has been sequestered and the patient must lodge a complaint with the police so that they can seize the sample and test it in a lab that allows the result to stand up as evidence in court. That is a matter of protecting the victim.

Once upon a time, we were naive and even though the requisition requested rohypnol (flunitrazepam) and the appropriate red flags went up, the GP lied to us and told us that it was clinical, not medical legal, and he was concerned it was contributing to her tremors so we should definitely do the test.

It is a benzodiazepine and our mass spec method is not really good at detecting benzos. Flunitrazepam is also a very low dose drug so our chances of finding it were spotty at best. So we ran it on the gas chromatograph which is no where near as specific as a GSMS but had a method developed for other benzodiazepines. To make things even more sketchy, we don’t and never really had a fully developed method for date rape drugs and the test was tailor made for this one time use by our lab scientists. Our big mistake was performing the test and sending out the report with “Flunitrazepam suspected.”

Several days later, the lab was getting calls from the woman’s lawyers. As it turns out, her husband was drugging her and taking advantage of her, but our results cannot be used outside of a clinical setting, especially not a result like that one. The police ended up seizing the sample anyways. The consequence was that we had used up a good portion of the sample and it took the forensics lab months and months to work out a method that could run the small quantity. 

Good news is he was tried and convicted in the end. And also that we learned our lesson.

joeyisqueen asked: Hi! I'm taking medical science and was wondering if you know if there's a book out there with practice CSMLS questions? Thanks :)


I don’t think there is a book (that I know of), but our instructors kept old copies of the exams for us to practice from, so you can try asking them? I guess my only tip is that when you register for the exam, you also get an MLT competencies list. That is the list of competencies that they have chosen to build the exam out of and you should definitely focus on those.

Also, don’t get too nervous! It is very, very entry level. So entry level that even basic mycology is considered too advanced to be on it. I literally started studying the night before* and did just fine. It is more of a test of endurance than knowledge for sure.

Sorry for the roundabout answer. Goodluck on your CSMLS exam!

*This will be tough if you have a lot of notes. I happen to have kept very condensed notes and my entire program basically fit onto 20 sheets of printer paper. 

I feel as though I have reached a new level of gross in the specimens we receive. Nothing quite as horrifying as kidney worms though. The other day as I was walking past the extraction bench for the GC mass spec, I noticed a very distinct alcohol odor. When I looked over, there was a sample cup full of greenish chunky vomit.

Someone had requested an alcohol level on puke.

Alcohol levels are actually done on the GC headspace, not the GCMS. Instead of sampling the extract, the instrument makes use of the volatility of alcohol and samples the space above the sample. The result is a much cleaner and easy to interpret chromatogram. That being said, they don’t have a method in place for extracting vomit (That is more the Medical Examiner’s Office’s domain) and we had to reject the request.

Our GCMS doesn’t do levels and is a qualitative method. Reason being is that 99.9% of our samples are urine (sometimes serum/plasma and syringe contents) and knowing how much of a drug is in the urine literally tells you nothing. It won’t tell you how much the person took, nor when they took it, not if they are a regular user or not, not even if it has any relevance to their clinical presentation (if overdose is suspected). 

Something all toxicology labs have but don’t advertise is their stock of drug standards that they use for building drug libraries on our instrument, reagent preparation, and controls. Getting even a single ampoule (1mg/mL) involves lots of hoops since the bigwigs need to feel comfortable with people having a freezer full of ultra pure, ultra concentrated (street)drugs.

So, after 8 months of hard lobbying and everyone signing their life away, we finally got approved by the federal government and got our hands on drug standards for desomorphine, better known on the internet for its hype in Russia under the name Krokodil.

You may also be interested to know that its ion profile on the mass spec is shockingly similar to dextromethorphan, the cough syrup. 

When we send results, the laboratory information system sometimes automatically appends reporting comments to help physicians interpret the results. 

Recently, a new comment has attached itself onto Benzodiazepine results on the drug screen saying that Oxaprozin (AKA DayPro) can produce false positive results for up to 10 days. This is strange because the benzo screen was supposed to be pristine but apparently this new fangled drug will cross react in the assay.

How that comment came to be was interesting.

Our esteemed toxicologist (who often donates his body to such pursuits), took four days worth of this prescription medication at maximum dose and collected his own urine to throw on the cobas analyzer and, lo and behold, was positive for benzodiazepines for 10 days.

And thus a reporting comment was born.

Lately I have been working on transitioning to a new position in Toxicology, which is less of a toxicology department now that it has basically adopted all the labour intensive expensive tests for the lab, almost all of which are some form of chromatography with long, painful manual extraction processes. 

On my first day I was greeted with a request for a cannabinoid confirmation on a newborn (literally newborn). 

It came back strongly positive and we reckon mom decided to smoke some marijuana to help with her pregnancy. I hope it was worth it to her knowing that her baby is quite possibly going to have neurodevelopmental problems.

Unfortunately, this kind of experience will be par for the course in the new position, as we will get a lot of addicts (to harder drugs) who give birth to poisoned babies. 

Now that I work in a private lab and not a hospital lab, poor collections are less of an issue for a number of factors. While non-lab-staff (who sometimes do collections in certain departments/hospitals) think we are just being huge jerks when we tell them they did it wrong, there are actually very real consequences for a poor collection.

An example is a nice elderly lady who had gone into emergency and the physician suspected she was going into renal failure. Her initial bloodwork gave the following results (reference ranges in brackets):

Creatinine: 40umol/L (50-105umol/L)
Sodium: 148mmol/L (133-146mmol/L
Chloride: 122mmol/L (96-106mmol/L)
Hemoglobin: 97 g/L (120-160g/L)
White blood cells: 4.0x10^9/L (4.0-11.0 x10^9/L)

Based on these results, the creatinine is way too low to fit renal failure. In fact, it is suspect for other metabolic conditions like liver disease. But her sodium and chloride are quite high. Chloride that high can suggest a number of things, including metabolic acidosis. Hemoglobin is low, and it’s around the point where some physicians would want to give a transfusion, depending on the patient status. The patient was admitted and had followup bloodwork 6 hours later:

Crea: 87umol/L
Na: 140mmol/L
Cl: 111mmol/L
Hgb: 122 g/L
WBC: 9.6x10^9/L

That’s… Quite different! The patient never got transfused or anything (and didn’t even really get much treatment, actually) and that is a huge climb in hemoglobin (a full unit of packed cells would only increase her hemoglobin by about 10g/L as it were). The fact that many things have practically doubled would have made the analyzer flag the results as suspect (AKA failed delta). Notice that the sodium and chloride, previously high, have gone down. Overall, her results are actually quite nice.

But we would have to look into the delta flag either way because that is what we do. After retrieving the first sample from the fridge and comparing it to her current sample, you could see right away there was A Problem. No pictures, unfortunately, but the serum was much more dilute, almost clear, on the chemistry tube from her first draw. Not to mention the hematocrit (ratio of blood cells to plasma) was much, much lower on the first collection. 

Knowing that isotonic saline has a sodium of 150mmol/L, the individual who did the first collection had probably skipped phlebotomy 101 and decided it was ok to collect right above an IV site, causing her specimen to be diluted down.

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