Understanding Drug Testing: Insights and Considerations

 
Interpretation of Drug Tests
 
Randall L Tackett, PhD
University of Georgia College of Pharmacy
706-542-5415
rtackett@me.com
 
Drug Testing
 
 
The basic assumption is that a blood or urine
drug level is directly correlated to a level of
impairment.
Reality:  This is not always the case
 
Type of Test
 
Drug Screen (EMIT, RIA)
Positive if above a cut-off
Negative if below cut-off
Does not provide quantification
Highly subject to interferences
Confirmation test
GC/MS
“Fingerprint of drug”
Identifies specific drug and quantitates
 
Cut-off Values
 
Substance Abuse and Mental Health Services Administration (SAMSHA)
specifies cut-off values
SAMSHA requires 5 drug categories to be routinely included in urine
screens
Amphetamines (methamphetamine, amphetamine, MDMA)
Cocaine metabolites
Marijuana metabolites
Opiate metabolites (morphine, codeine, 6-actylmorphine)
Phencyclidine
In specific cases, cutoff values may be lowered
 
Type of Test
 
Hospital vs  Forensic Testing
Generally a screen
Not intended to quantitate
Usually has a disclaimer on lab report that results
should not be used for legal purposes
 
Type of Testing
 
Hospital alcohol testing
Measures alcohol dehydrogenase based assay
Usually is measuring serum or plasma rather than
whole blood
Subject to interferences
Other alcohols
Lactate  and LDH (lactate ringer’s solution; muscle damage)
Varies with test
 
Testing Conditions
 
Calibration of instrument
Appropriate standards
Standard curves
Linear?
Sample between calibrators
 
Testing Conditions
 
What  was tested?
 
Breath
Blood
Serum
Whole blood
Urine
 
What was tested?
 
Whole blood vs Serum (ethanol)
Serum contains a greater water content than whole
blood
Since ethanol distributes in water content, greater
ethanol concentration in serum than whole blood
Whole blood alcohol concentration = serum alcohol
concentration/1.14
 
What was tested?
 
Urine
Longer period of detection
If in urine, not acting in tissue
Metabolite
Active vs inactive
 
Characteristics of Specimens
 
Urine – window of detection typically 1-5 days;
Can be adulterated
Shy bladder
Hair – longest window of detection
Usually 90 days based on collection of 1.5 in of hair (0.5 in/month)
Non-invasive
Expensive
Will not detect recent use (7-10 days prior to test)
 
Characteristics of Specimens
 
Saliva – reflects recent use (10-24 hrs)
Noninvasive
Drugs and metabolites do not remain in sample long
Limited value
Sweat – limited value
Few labs perform test
 
Administration
 
 
Route of administration
How long has patient taken drug
Is patient taking drug regularly
Therapeutic window
Winek
Basalt
 
 
 
Detection Times - Urine
 
Tolerance
 
Tolerance is dynamic – it increases and
decreases
Varies between individuals
Tolerance affects both the therapeutic effects
and toxic effects of a drug
 
Is drug prescribed?
 
Was the drug prescribed for the person or
someone else’s medication?
When was it prescribed – old vs current
prescription?
Drug interactions
 
Are client’s symptoms consistent with drug?
 
What symptoms of impairment were noted at
the time of arrest?
Are they consistent with pharmacology of
drug
Alternative explanation for behavior noted?
 
Interpretation of Drug Tests
 
Indicates that drug has been ingested
Unlikely to be able to relate to level of impairment
Usually not able to determine when most drugs were
ingested
Requires confirmation test
Screening test not sufficient for determining exposure
 
21
 
Summary
 
Type of testing?
Testing conditions?
What was tested?
Administration
Tolerance
Is drug prescribed
Symptoms consistent with pharmacology
 
 
 
 
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Drug testing interpretation is not always straightforward as the correlation between drug levels and impairment varies. Different types of tests, such as EMIT and GC/MS, provide different levels of detail and accuracy. Cut-off values are specified by SAMSHA, and testing for alcohol can be subject to various interferences. Understanding the nuances of testing conditions and the types of substances tested is crucial for accurate interpretation.


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  1. Interpretation of Drug Tests Randall L Tackett, PhD University of Georgia College of Pharmacy 706-542-5415 rtackett@me.com

  2. Drug Testing The basic assumption is that a blood or urine drug level is directly correlated to a level of impairment. Reality: This is not always the case

  3. Type of Test Drug Screen (EMIT, RIA) Positive if above a cut-off Negative if below cut-off Does not provide quantification Highly subject to interferences Confirmation test GC/MS Fingerprint of drug Identifies specific drug and quantitates

  4. Cut-off Values Substance Abuse and Mental Health Services Administration (SAMSHA) specifies cut-off values SAMSHA requires 5 drug categories to be routinely included in urine screens Amphetamines (methamphetamine, amphetamine, MDMA) Cocaine metabolites Marijuana metabolites Opiate metabolites (morphine, codeine, 6-actylmorphine) Phencyclidine In specific cases, cutoff values may be lowered

  5. Type of Test Hospital vs Forensic Testing Generally a screen Not intended to quantitate Usually has a disclaimer on lab report that results should not be used for legal purposes

  6. Type of Testing Hospital alcohol testing Measures alcohol dehydrogenase based assay Usually is measuring serum or plasma rather than whole blood Subject to interferences Other alcohols Lactate and LDH (lactate ringer s solution; muscle damage) Varies with test

  7. Testing Conditions Calibration of instrument Appropriate standards Standard curves Linear? Sample between calibrators

  8. Testing Conditions

  9. What was tested? Breath Blood Serum Whole blood Urine

  10. What was tested? Whole blood vsSerum (ethanol) Serum contains a greater water content than whole blood Since ethanol distributes in water content, greater ethanol concentration in serum than whole blood Whole blood alcohol concentration = serum alcohol concentration/1.14

  11. What was tested? Urine Longer period of detection If in urine, not acting in tissue Metabolite Active vs inactive

  12. Characteristics of Specimens Urine window of detection typically 1-5 days; Can be adulterated Shy bladder Hair longest window of detection Usually 90 days based on collection of 1.5 in of hair (0.5 in/month) Non-invasive Expensive Will not detect recent use (7-10 days prior to test)

  13. Characteristics of Specimens Saliva reflects recent use (10-24 hrs) Noninvasive Drugs and metabolites do not remain in sample long Limited value Sweat limited value Few labs perform test

  14. Administration Route of administration How long has patient taken drug Is patient taking drug regularly Therapeutic window Winek Basalt

  15. Detection Times -Urine Drug DetectionTime Amphetamine 2-5 days, possibly 2 weeks with heavy use Cocaine metabolites (benzoylecgonine) Up to 2 weeks; 6 weeks w/chronic use LSD 1-2 days Marijuana metabolite (COOH) 7-10 days; 1 month chronic use Opioids 2-3 days Methadone 3-14 days PCP 2-10 days

  16. Tolerance Tolerance is dynamic it increases and decreases Varies between individuals Tolerance affects both the therapeutic effects and toxic effects of a drug

  17. Is drug prescribed? Was the drug prescribed for the person or someone else s medication? When was it prescribed old vs current prescription? Drug interactions

  18. Are clients symptoms consistent with drug? What symptoms of impairment were noted at the time of arrest? Are they consistent with pharmacology of drug Alternative explanation for behavior noted?

  19. Interpretation of Drug Tests Indicates that drug has been ingested Unlikely to be able to relate to level of impairment Usually not able to determine when most drugs were ingested Requires confirmation test Screening test not sufficient for determining exposure 21

  20. Type of testing? Summary Testing conditions? What was tested? Administration Tolerance Is drug prescribed Symptoms consistent with pharmacology

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