A common misconception among forensic witnesses is that a blood drug result, by itself, predicts the pharmacologic effect including toxicity and impairment. This misconception is especially prevalent among forensic witnesses with inadequate formal higher education and training in pharmacology and universally present in those witnesses with no clinical (hands on) training practicing medical pharmacology on people.
A three prong argument exists that explains why the misconception exists.
1. The blood sample and its analysis
The first step in any blood drug case is to request from the testing laboratory the forensic documents that describe in detail the acquisition of the blood sample including the initial blood draw and its subsequent transport and storage. These documents are called the “Laboratory Litigation Package” and are standard documents used in the forensic profession for an expert to review. 1 An example documents request template is found at the end of this discussion.
Those documents must show that the blood draw was performed in a forensically proper manner and that the chain of custody was intact for the blood draw and during transportation and storage.
The documents must also show that the testing performed was performed in a forensically proper manner and must publish the total error that is associated with the quantitative result, also known as the ‘uncertainty” determination.
All of the errors found in the review of the blood sample and its testing reduce the forensic reliability of the test result and must be taken into consideration regarding any interpretations of the drug test result.
For example, many blood tetrahydrocannabinol (THC) tests have a large uncertainty due to the nature of the test procedures used, up to plus or minus 40% of the quantitative result. That uncertainty is large enough to make the quantitative result prejudicial regarding the person tested. 2
2. Forensic witnesses usually rely on the blood drug test result to predict the drug concentration at the time of an incident or death
Even if a blood drug concentration could predict the effect of the drug in an individual (and, with emphasis, that is simply not true) in antemortem (before death) cases the blood drug concentration is a constantly moving value so the only way to know the blood drug concentration at any specific time is to collect a blood sample at that specific time. Usually the blood sample in forensic cases is collected an hour or more after a specific incident. 3 Therefore the witness never knows the true blood drug concentration at any time before the blood sample was collected.
A graphic example of the change in blood drug concentration over time is shown below. 4 This graph shows the type of dramatic change in blood concentration that may occur over time. MEC is for the minimum effective concentration.
In postmortem cases the blood drug concentration results are distorted due to movement of the drug in the postmortem remains from one anatomic site to another anatomic site.
For example, when alive a drug may be concentrated in the heart muscle but after death the drug may be released from the heart muscle into the blood inside the chambers of the heart. This postmortem redistribution of the drug from the heart muscle to the heart blood increases the blood concentration and results in a falsely elevated blood drug concentration when the blood sample is collected from the heart chambers. Many other examples of postmortem drug redistribution exist. 5
Although many forensic witnesses believe that the postmortem blood drug results reflect the concentration of the drug in the circulating blood just before death, the scientific evidence supports just the opposite. Postmortem blood drug results do not predict the antemortem blood drug levels and the interpretive value of the postmortem blood drug results are often quite limited. 6
Postmortem blood drug results have their greatest reliability when collected at the time of death. As the postmortem interval increases, the forensic reliability of the blood drug results decreases quickly with a concomitant decrease in interpretive trustworthiness.
3. Even if a blood sample is collected at the time of an incident or death the drug concentration cannot determine drug effect by the blood test result alone
Medical drug concentrations in the blood are studied in populations of people to determine safety, efficacy and toxicity and this area of medical pharmacology and medicine is regulated by the Food and Drug Administration (FDA).
However the study of a drugs effect in a population of people does not and cannot predict the effect of any drug in any specific living individual based on a blood drug result. Individuals in a population exhibit large differences in the effects of drugs at the same dose and at the same blood concentration. This concept is current medical pharmacology doctrine and supported by a large body of evidence created over the last one hundred years or so.
Postmortem drug results suffer from the large confounder of postmortem redistribution as discussed previously, so those drug test results are less reliable thus less trustworthy compared to any antemortem test results.
Antemortem blood drug test results may be helpful in combination with more information in a given forensic case such as reliable behavioral observations, clinical examinations and testing information, and audio and video recordings of the person before, during and after an incident.
Postmortem blood drug test results are more limited compared to antemortem blood drug test results but may have some utility in conjunction with the same type of information that may be used in an antemortem case.
- 2006 S.O.F.T. Laboratory Guidelines, Section 11.10 Litigation Packs
- Author’s personal experience with actual forensic casework
- Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 12th Edition
- Pounder, D.J., Post-Mortem Drug Redistribution – A Toxicological Nightmare, Forensic Science International, 45 (1990) 253-263
- Cook, D.S., Estimating antemortem drug concentrations from postmortem blood samples: the influence of postmortem redistribution, J Clin Pathol 2000;53:282–285
- Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 13th Edition
Laboratory Litigation Package Template © UMFC, LLC. 2020
Very Important – please provide the documents and files as an electronic PDF file in the numerical order of this document, with a table of contents and appropriate pagination and in color when the original document is other than black and white
- A clean copy of the laboratory quality manual or equivalent document
- A clean copy of the laboratory Standard Operating Procedure manual or equivalent document
- A clean copy of all instruction materials, textbooks, references, and/or publication citations used in the formal training of any person involved in the analysis of the sample(s) in question
- A copy of all instructors and their curriculum vitae involved in the training of any person involved in the analysis of the sample(s) in question
- a copy of all of the chain of custody documents including intra-laboratory documents for the sample(s) in question
- a copy of the analytical method used to perform all analytical tests on any specimen including the written method, the analytical instrument manufacturer, model and serial number. Also, the method software used and the method software settings and any method validation studies performed for the test results in question
- a copy of all maintenance records of the instrument used in the analysis for previous 12 months including any software and/or hardware updates, patches, repairs, replacements
- a copy of any repair records of the instrument used in the analysis for the previous 12 months
- a copy of the qualifications, certifications, licenses, and permits of any individual performing analysis of the specimen in question
- a copy of the instrumental raw data of all quality control and calibrator tests performed during the analysis of the defendant samples in question (on CD or flash drive)
- a copy of the instrumental raw data of the analytical tests performed on all the defendant samples themselves (on CD or flash drive)
- a copy of the instrumental raw data of the analytical tests performed on all proficiency samples analyzed for the twelve-month period prior to the defendant sample (on CD or flash drive)
- a clear high-resolution copy of all chromatograms, mass spectrograms, and or absorbance spectrometry printouts and calibration tables of all calibrators, controls and all samples in the batch of samples in question
- a clear high-resolution copy of all chromatograms, mass spectrograms and or absorbance spectrometry printouts and calibration tables of any reference standards used in the method validation or sample analysis
- quality control data (e.g. Levi-Jennings charts) for the previous six months for any analysis reported out of the samples in question
- a copy of any proficiency tests performed for a given analysis (blood ethanol, blood drug, urine drug) during the most recent six-month period
- calibration data for any weight and measuring device used in the analysis (i.e., pipettors, balances and scales)
- sample worklist and chromatograms, mass spectrograms and results for all samples analyzed with the subject (defendant) samples
- a description of the samples analyzed including high resolution digital color photographs of all the physical evidence, specimen type, amount, collection (storage) container (including legible original manufacturer blood tube label), current availability and temperature history of the defendant samples from the time of initial collection to current date
- A copy of all correspondence (including emails and hand written notes), regarding the testing of any and all samples in this case
- A description and documentation of laboratory compliance with ASTM / ISO 17025 or ASTM / ISO 15189 standards if such compliance was in effect when the subject sample(s) were tested including any statement of uncertainty regarding the quantitative results and all data and calculations used in the determination of any statement of uncertainty
- If no ASTM / ISO standard was in effect, then a description and documentation of the good laboratory standard that was in effect when the subject sample(s) were tested including any statement of uncertainty regarding the quantitative results and all data and calculations used in the determination of any statement of uncertainty
- The current good laboratory standard in effect if different than included in 17), 18) above including any statement of uncertainty regarding the quantitative results and all data and calculations used in the determination of any statement of uncertainty
- A copy of all documents transmitted in any fashion to and from the laboratory and any accreditation entity during the initial accreditation, re-accreditation and the accreditation period in effect at the time of the subject sample test results
- A copy of any notification of any type regarding any product recalls or warnings of any equipment, device, reagent, expendable, software or evidence used in the case.
- Please provide any and all personnel files regarding any disciplinary actions of any kind.
- If any items are not provided or are incomplete, please provide a detailed explanation for each item.
- If any of these enumerated items have been destroyed please indicate each item, method of destruction, and date of destruction and reason for destruction.