Clinical Tox Testing Flashcards
specimens for clinical tox testing
urine = specimen of choice
serum, blood (usually for TDM; if kidney failure and cant produce urine we may want to use this)
gastric (more important what’s absorbed, not what throwing up)
hair
meconium
sweat
oral fluid
umb cord tissue and blood
placenta
why is urine preferred for tox screen?
- conctn of drugs higher than in blood/serum
- easy to collect in sufficient volumes
- metabolite detection
- screening assay compatibility
urine limitations
no relationship between detected and..
- actual ingestion time
- amount ingested
- frequency of use/abuse
- degree of impairment
- determining conctn does NOT overcome these limitations
difficult drugs = methylphenidate (Ritalin), oral hypoglycemics
amphetamin general retention time
up to 4 days
MDMA/ecstasy general retention time
up to 4 days
marijuana metabolite general retention time
up to 30 days (chronic vs occasional)
cocaine metabolite general retention time
up to 4 days
opiates general retention time
up to 3 days
heroin metabolite general retention time
less than 1 day
barbiturates general retention time
days to weeks
benzodiazepines general retention time
days to weeks
methadone general retention time
up to three weeks
general retention time of alcohol
less than 1 day
immunoassay for clinical drug testing
initial testing
antibody-antigen rxns
refers to instrument based and non-instrument based techniques (POCT)
designed to detect broad class of drugs
limited in scope (limited assays)
cross-reactivity (ability to detect drug) dependent on reagent chemistry and devices used
prone to false negs and false pos
main advantage of immunoassay
relatively fast
main disadvantages of immunoassay
no immunoassay is absolute
it can be 100% right or 100% wrong
due to the false pos and false negs it may not be an accurate reflection of drug use
KIMS
kinetic interaction of microparticles in solution
principle of KIMS
competitive homogenous immunoassay
components of KIMS
R1: drug derivatives conjugated to aminodextran
R2: microparticles covalently coated with Ab
enzyme multiplied immunoassay technique
EMIT
what are false negatives of immunoassays due to?
- cut-offs are subjective (based on employment ‘rules’)
- assay too specific (cocaine metabolite)
- variance in antibody cross-reactivity within a drug class:
> amphetamines
> opiate: semi-synthetics
> benzos: glucuronide metabolites (lorazepam, temazepam)
confirmatory testing main advantase
definitive
main disadvantage of confirmatory testing
more resource driven compared to immunoassay
STAT tox testing
- not recommended
- quality tox testing is rarely of any valye in emergency situations for several reasons
> does not confirm/rule out significant poisoning
> almost never provides info that leads to a meaningful change in acute medical management
> countless drugs contribute to common clinical symptoms seen in emerge that are not tested for immunoassay screening
> testing not specific
> pos test does not mean that it’s what’s contributing to pt’s symptoms - provincial initiative
T or F. We use clinical tox testing for drug-facilitated assault
F! use for CLINICAL management of patients only
- not for employment-related purposes, insurance purposes, drug-fac assault, accident investigation/impaired driving, apprehending children under child and family services authority, etc.
cannot be used as a measurement of impairment and determining compliance is challenging!
Benzodiazepines (KIMS)
- tends to be fairly specific
- some benzos more detectable than others
- metabolite cross-reactivity can be poor
- Oxaprozin or Daypro can cause false pos
- cross-reactivity table
these benzos are not picked dup well by the KIMS assay
Lorazepam glucuronide (> 20 000)
Temazepam glucuronide (> 20 000)
GC/MS or LC/MS/MS Testing for drugs
- more resource driven than immunoassay
- gives a fingerprint of drug based on retention time and fragmentation pattern
- identify specific compounds
- considered confirmation tests
- poor extraction, poor chromatographic properties of some drugs limit detection
baseline integrity testing
temp
testing for adulterants
pH
nitrites
hexavalent chromium
surfactants, etc.
testing for substitution
creatinine
specific gravity
hydrocodone
not a metabolite of oxycodone
rather a physical impurity
