Chapter 20 — Self-Check Quiz

26 questions: multiple choice and short answer. Try them closed-book. The answer key is in the collapsed block at the bottom.

Multiple choice

1. The "first question" of forensic toxicology — the one it answers most reliably — is: - A. Was the person impaired at the time of the offense? - B. What substance is present? - C. Who administered the drug? - D. Was the death a homicide?

2. Certainty in a toxicology result is highest for: - A. Interpretation of effect - B. Identification of the substance - C. Estimating impairment at a past moment - D. Determining the manner of death

3. An immunoassay screen detects: - A. A single, specific molecule with no possibility of error - B. A drug class by molecular shape, with a risk of cross-reactivity - C. The exact concentration with certainty - D. The manner of death

4. The defining weakness of an immunoassay, which makes it presumptive only, is: - A. It is too slow and expensive - B. Cross-reactivity (structurally similar substances can trigger a false positive) - C. It destroys the sample - D. It cannot detect alcohol

5. A confirmatory test must rest on a chemical principle that is: - A. Identical to the screen, for consistency - B. Different from the screen, so a cross-reactant cannot fool both - C. Cheaper than the screen - D. Faster than the screen

6. The gold-standard confirmatory technique in toxicology (detailed in Chapter 23) is: - A. A second immunoassay - B. A color-change field test - C. Gas chromatography–mass spectrometry (GC-MS) - D. Visual inspection

7. Blood is the specimen of choice for impairment questions because: - A. It is the easiest to collect - B. Its concentration is most closely tied to what was active in the body at the time of sampling - C. It never changes after death - D. It detects exposure over months

8. Urine is best suited to answer: - A. Whether the person was impaired at a precise moment - B. Recent exposure over roughly the last few days - C. The exact blood concentration at death - D. The manner of death

9. Vitreous humor is forensically valuable in death investigation largely because it is: - A. Present in large volume - B. Anatomically isolated and slower to decompose, resisting some postmortem artifacts - C. A perfect one-to-one match for blood concentration - D. Useless for alcohol

10. Hair analysis is most often over-read because of: - A. Its inability to detect any drugs - B. External contamination, which can produce positives unrelated to ingestion - C. Its perfect timing precision - D. The fact that it decomposes within hours

11. A metabolite is: - A. The original drug before the body changes it - B. A product the body makes when it chemically transforms a substance, usually toward elimination - C. A type of immunoassay - D. A postmortem artifact only

12. Paracelsus's principle, "the dose makes the poison," means: - A. Some substances are poisonous and others are always safe - B. There is no poisonous substance in itself — only a quantity that is harmful - C. Poisons cannot be measured - D. Every drug found in a body caused harm

13. A drug found in the therapeutic range is most consistent with: - A. A fatal poisoning - B. Appropriate medical use - C. Incapacitation in every person - D. Postmortem production

14. Tolerance matters to interpretation because it can: - A. Make the instrument misread the concentration - B. Shift an individual's entire effect scale, so a "lethal-range" level may be survivable for a chronic user - C. Eliminate the drug from the blood - D. Convert urine into blood

15. Retrograde extrapolation of BAC assumes the person was: - A. Still absorbing alcohol - B. Past peak and eliminating - C. Not drinking at all - D. Dead at the time of the draw

16. The same measured BAC can correspond to a lower crash-time value if, at the time of the crash, the driver was: - A. Eliminating - B. Still absorbing (on the rising limb) - C. Sober - D. Already past peak for many hours

17. A per se alcohol limit (e.g., 0.08) exists in part because: - A. The law can perfectly measure individual impairment - B. Proving individual impairment from a number is hard, so the legislature makes the measurable number itself the offense - C. BAC has no relationship to impairment - D. Breath testing is illegal

18. Postmortem redistribution (PMR) describes: - A. An instrument error that misreads the concentration - B. The postmortem leakage of drugs from organs into nearby (especially central) blood, raising that blood's concentration above the antemortem level - C. The body eliminating all drugs after death - D. A type of confirmatory test

19. To limit the effect of PMR on interpretation, the best blood specimen is: - A. Heart (central) blood - B. Femoral (peripheral, leg-vein) blood - C. Brain tissue only - D. Hair

20. Postmortem alcohol formation (neoformation) is a concern because: - A. Alcohol always disappears after death - B. Bacteria can produce ethanol in a decomposing body, so a measured BAC may overstate or fabricate antemortem drinking - C. It makes hair testing more reliable - D. It only affects living subjects

Short answer

21. In two sentences, explain why the certainty of a toxicology result "drains away" from the first question (what) to the third (so what), and name the source of authority for each kind of statement.

22. A screen is positive; the confirmation is negative. Which result goes in the report as the identification, and why? Use the "metal detector and hand search" analogy.

23. Explain why a positive urine result cannot establish impairment at a specific moment, using the distinction between exposure and effect.

24. A blood opioid concentration is in the textbook "lethal range." Give two reasons this does not, by itself, prove the opioid caused the death.

25. Explain why blood drawn from the heart can mislead in a postmortem case while blood from a femoral vein is less likely to, and why this is an interpretation problem rather than an instrument error.

26. In the cold case, the toxicology found a sedative at an incapacitating level and a modest BAC. Write one sentence an honest expert could say on the stand about what this establishes, and one sentence that would overstate it.

Answer key (click to expand) **Multiple choice:** 1-B · 2-B · 3-B · 4-B · 5-B · 6-C · 7-B · 8-B · 9-B · 10-B · 11-B · 12-B · 13-B · 14-B · 15-B · 16-B · 17-B · 18-B · 19-B · 20-B **Short answer (model points):** **21.** The first question is answered by an *instrument* (identification against reference libraries, low measurable error); the second by a *calibrated measurement* (quantitation with stated uncertainty); the third by a *human judgment* built from the number plus tolerance, timing, combinations, and postmortem chemistry that the instrument does not measure. Certainty drains away because each step adds assumptions the instrument cannot verify — the authority shifts from chemistry to pharmacology to inference. **22.** The **confirmation (negative)** governs: only a confirmed result is a forensic identification, and a confirmatory method rests on a different chemical principle than the screen, so it can identify the actual compound rather than merely react to a class. By analogy, the screen is the metal detector (deliberately over-sensitive, beeps at belt buckles); the confirmation is the hand search that determines what actually set it off — and only the hand search goes in the report. **23.** Urine concentrates drugs and especially metabolites for excretion, so a positive can reflect *exposure* days earlier, long after any impairment has passed. It measures that the drug was in the body and was processed (*exposure*), not whether it was active in the bloodstream at a given moment (*effect*); a cannabis-metabolite positive in particular can persist well beyond impairment. **24.** Any two, e.g.: (a) **tolerance** — a chronic user may function at, or survive, a concentration that is "lethal" for a naive person, so the range is a population guide, not a per-person verdict; (b) the **ranges overlap and are blurry**, drawn from population data with wide variation; (c) the concentration may reflect **postmortem redistribution** (if from central blood) rather than the antemortem circulating level; (d) cause of death is an *interpretation* requiring the whole picture (history, other findings), not a number read off a table. **25.** After death the body's barriers break down and drugs leak from organs (liver, lung, heart) into adjacent central blood, so heart-blood concentrations can be artifactually elevated above the antemortem level (postmortem redistribution); femoral (leg-vein) blood is far less affected and more antemortem-representative. The instrument measures the central-blood concentration *accurately* — the problem is that that concentration no longer *represents* the death-time level, which is an interpretation problem, not a measurement error. **26.** **Honest:** "A sedative was confirmed in peripheral blood at a toxic, incapacitating concentration, and a modest blood alcohol level was present; interpreted against the sampling and the individual, this strongly supports that the victim was chemically incapacitated before death — it does not identify who administered the sedative or establish it as the cause of death." **Overstated:** "The toxicology proves the defendant drugged and killed the victim with the sedative."