Drug and alcohol testing – Forensic facts and fine points

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Drug Tests Sign for DriversGuest post by Dr. Michael Robertson – Independent Forensic Consulting

Dr. Robertson is a forensic toxicologist at Independent Forensic Consulting and a consulting toxicologist at Australian Workplace Drug Testing Services and Australian Forensic Drug Testing Services. He is also a specialist consultant to Medilaw. Dr. Robertson graduated with a Doctor of Philosophy in Forensic Medicine from Monash University with a background in pharmacology, toxicology and analytical chemistry and has spent the past 13 years in various laboratories performing and reviewing most types of traditional and state of the art techniques, acquiring extensive knowledge of forensic toxicology, analytical testing and interpretation and various codes of manufacturing requirements.

How to Calculate a Blood Alcohol Concentration (BAC) from a Plasma or Serum Alcohol Concentration

Alcohol prefers to ‘live’ in water so when alcohol is measured in serum or plasma samples the alcohol levels will be higher in serum than the respective blood concentration by approximately 10% to 15% and up to 35% higher in plasma:

  • First establish if the alcohol reading is from a serum or plasma sample – hospital records should make this clear
  • If the result is in mmol / L convert to mg/dL by multiplying the value by 4.6
  • A BAC of 0.05% is equivalent to 50 mg/dL; 0.05 g/100mL
  • For serum, divide the reading in mg/dL by 1.15 to get the lower value of the range and divide the reading in mg/dL by 1.10 to get the higher value of the range
  • For plasma, divide the reading in mg/dL by 1.35 to get the lower value of the range and divide the reading in mg/dL by 1.10 to get the higher value of the range

Although there are always variables that make each matter somewhat unique, using these well established and generally accepted ranges, these results will give you an indication if the matter is worth engaging an expert.

Hair Testing – The Basics Analysis of hair is particularly useful when other samples such as blood and urine are no longer useful i.e. after a few days or if chronic use of drugs is required to be confirmed or denied. Common applications for hair testing include determining of someone is a chronic user of drugs; drug-facilitated sexual assault; poisonings; testing for compliance i.e. to ensure someone is taking their medication.

  • Drugs are incorporated into hair at the time of drug use & may be detectable for months or years after last use, depending on hair length
  • Hair is an effective sample type to confirm drug use or provide supportive evidence of abstinence
  • Hair is an easily obtained and analysed sample and results are generally accepted in Australian Courts
  • Testing is available routinely in Australia and NZ
  • Hair growth rates approximate 1 cm per month i.e. the 6 cm closest to the scalp represents the last 6 months hair growth and drug use
  • Drug levels in hair may be affected by hair colour, bleaching, straightening, UV light etc.
  • A positive result implies chronic or repetitive use during the period represented by the hair sample
  • A negative result may indicate a) no use b) little use c) a degraded hair sample d) the hair sample tested does not reflect the time of drug use
  • Hair can be segmented to demonstrate a profile of drug or poison exposure
  • Single use can be detected in DFSA can be determined in most cases

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Date Published: 21 December 2011

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