Toxicology

Question 1

What are the various specimens you can use to evaluate for drug use?

Answer 1

urine
blood
hair
saliva
sweat
nails

Question 2

Why do we usually do urine drug screens?

Answer 2

drugs and metabolites tend to be higher longer in the urine than serum

Question 3

What is the basis for most of the drug screening assays?

Answer 3

most are immunoassay based, so use antibodies to identify drug or drug class

because of this, cross-reactivity is common and critical to recognize

Question 4

In general, what is the basis for confirmatory testing?

Answer 4

usually gas or liquid chromatography mass spect

(the nice thing about them is they can identify drugs with certainty, but you need to know the specific drug to test for it - not good for screening)

Question 5

Urine from what time of day is the most helpful for drug testing?

Answer 5

early morning, because that’s when the drug will be at the highest concentration

Question 6

What are some tip-offs that someone has falsified their urine sample?

Answer 6

excessive bubble formation
it's cold
the pH is less than 3 or more than 11
the specific gravity is less than 1.002 (diluted) or greater than 1.020
Creatinine is less than 5 mg/cL

Question 7

What does the urine drug screen look for specifically when screening for cannabinoids?

Answer 7

11-nor-delta-9-THC-carboxylic acid

also metabolite of THC

Question 8

Why not just look for THC?

Answer 8

it’s highly soluble in lipids so has slow excretion into urine whereas the metabolites get there faster

Question 9

A single use of marijuana can result in a positive urine screen for how long?

Answer 9

up to 1 week

Question 10

Long-term use of marijuana can result in a positive screen for how long?

Answer 10

up to 46 days

Question 11

What are three common drugs that have been shown to cross-react with cannabinoid immunoassays?

Answer 11

NSAIDs (yikes)
efavirenz
PPIs
some antibiotics (quinolones)

Also hemp-containing foods and eye drops like visine!

Question 12

Why can someone on methadone have a negative opiate screen?

Answer 12

methadone is an opioid that interacts with the opioid receptor but has no chemical similarity to opiates and won’t cross-react with the reagent

Question 13

What do most amphetamine screens look for?

Answer 13

most do amphetamine and methamphetamine, but others do MDMA and MDA

others do the stimulants more broadly

Question 14

WHat are some drugs that will cause clinical false positives on amphetamine screens?

Answer 14

adderall

dexedrin

methamphetamine

selegiline

famprofazone (apparently it’s an alagesic and antipyretic)

Question 15

True or false: cross-reactivity allows for all benzodiazepines to be tested for using the same antibody?

Answer 15

nope

most of the benzo screening assays use antibodies directed against a single benzo