Lecture 16 - Clinical Toxicology Testing

Question 1

Why is urine the prefered specimen

Answer 1

• concentration of drugs usually higher
• easy to collect in sufficient volume
• metabolite detection
• screening assay compatibility

Question 2

What is the limitations of urine testing

Answer 2

no relationship between detection and:
* actual ingestion time (can give “windows”)
* amount ingested
* frequency of use/abuse
* degree of impairment
* determining concentration does NOT overcome these limitations

Question 3

What are immunoassay tests

Answer 3

• Antigen-Antibody reactions
• Refers to instrument based and non-instrument based
  techniques (POCT)
• Designed to detect a broad class of drugs
• Limited in scope (i.e. limited number of assays available)
• Cross-reactivity (the ability to detect a drug) dependent on
  reagent chemistry and devices used
• Prone to false negatives and false positive

Question 4

Advantage for immunoassay testing

Answer 4

relatively fast

Question 5

Disadvantages for immunoassay testing

Answer 5

• not absolute
• can be 100% right or 100% wrong
• not an accurate reflection due to false pos and false negs

Question 6

What is KIMS

Answer 6

kinetic interaction of microparticles in solution

Question 7

What is the principle of KIMS

Answer 7

competitive homogenous immunoassay

Question 8

What are the components of KIMS

Answer 8

R1: drug derivatives conjugated to aminodextran
R2: micro particles covalently coated with antibody

Question 9

What is EMIT and DRI test priniciple

Answer 9

reagent Ab stops G6PD from being active by binding, if the Ab binds patient sample instead then G6PD can be active

Question 10

What is the CEDIA test principle

Answer 10

if Ab binds reagent Ag it stops enzyme fragments from coming together, if it binds patient Ag then it can bind

Question 11

What causes false negatives in immunoassays

Answer 11

1. Cut-offs are subjective (based on employment “rules”)
2. Assay too specific (e.g. cocaine metabolite)
3. Variance in antibody cross-reactivity within a drug class

Question 12

What is used for confirmatory testing

Answer 12

GC/MS or LS/MS/MS

Question 13

Testing for specimen integrity

Answer 13

• Baseline integrity testing
• Testing for Adulterants
• Testing for Substitution
• Generally integrity testing more encompassing in
  employment related drug testing than in clinical
  laboratory