MLT GlobeForensic Science: Alcohol & drug testing
40 Forensic Science MCQs on Alcohol & drug testing with answers and explanations.
In the liver, ethanol is mainly oxidized to acetaldehyde by which enzyme?
Cytosolic alcohol dehydrogenase, using NAD+, converts most ethanol to acetaldehyde. The microsomal CYP2E1 system and catalase contribute smaller amounts, especially at high intake.
Acetaldehyde formed from ethanol is converted to acetate mainly by:
Mitochondrial aldehyde dehydrogenase (ALDH2) oxidizes acetaldehyde to acetate. Inherited low-activity ALDH2 variants or drugs such as disulfiram cause acetaldehyde build-up and flushing.
Blood for forensic alcohol analysis is usually collected into a grey-top tube containing:
The grey-top tube contains sodium fluoride as preservative and potassium oxalate as anticoagulant, giving a stable whole-blood specimen suitable for headspace gas chromatography.
Which skin preparation is appropriate before venepuncture for a legal blood alcohol test?
Alcohol-based swabs could contaminate the specimen or give grounds to challenge the result. Forensic protocols specify a non-alcoholic antiseptic, documented on the collection record.
The reference method for forensic blood alcohol quantitation is:
Headspace GC-FID samples the vapour above heated blood, separating ethanol from other volatiles such as methanol, acetone and isopropanol, and quantifying against an internal standard. Duplicate analysis is standard.
Evidential breath alcohol measurements are converted to blood alcohol using a blood-to-breath ratio of about:
At equilibrium, 2100 mL of alveolar air contains about as much ethanol as 1 mL of blood. Many jurisdictions set breath limits directly, avoiding conversion, but the ratio underlies breath testing.
Compared with drinking on an empty stomach, drinking alcohol with a meal usually:
Food delays gastric emptying, so ethanol reaches the small intestine more slowly and more undergoes first-pass metabolism. The peak is lower and occurs later.
Which specimen is most widely used for regulated workplace drug testing?
Urine is collected non-invasively in adequate volume, contains higher concentrations of drugs and metabolites, and has well-established cutoffs and validity tests. Oral fluid and hair are growing alternatives.
In regulated workplace testing, a urine specimen that is negative on the initial immunoassay is:
Only specimens at or above the initial cutoff proceed to confirmation. Specimens below it are reported negative, which is efficient because most workplace specimens are negative.
A collector checks a urine specimen's temperature within four minutes of voiding. The acceptable range is:
A freshly voided specimen should read 32-38 degrees C (90-100 degrees F). An out-of-range temperature suggests substitution or dilution and triggers an immediate directly observed recollection.
During a urine drug test collection, bluing agent is added to the toilet water mainly to:
Colouring the toilet water makes any attempt to dilute or substitute the specimen with it immediately visible. Other water sources are also secured during collection.
In workplace drug testing, the Medical Review Officer (MRO) is responsible for:
The MRO is a licensed physician who reviews laboratory results, interviews donors with non-negative results, and verifies results as negative when a valid prescription or medical explanation exists.
A blood alcohol concentration of 0.08 g/dL is equivalent to:
One gram equals 1000 mg, so 0.08 g per decilitre equals 80 mg per decilitre (80 mg/100 mL). Unit awareness is essential when comparing results with legal limits.
Once absorption is complete, blood ethanol in most adults declines at a roughly constant rate of about:
Because alcohol dehydrogenase is saturated at typical concentrations, elimination is approximately zero-order, averaging 15-20 mg/dL per hour. Heavy drinkers may eliminate faster, around 25-30 mg/dL per hour.
The Widmark formula is used in forensic practice to:
Widmark's equation relates alcohol consumed to expected blood concentration using body weight and a distribution factor (r), with a correction for elimination over time. It gives an estimate with considerable uncertainty.
The main reason sodium fluoride is used in blood alcohol specimens is to:
Contaminating yeasts and bacteria can ferment glucose to ethanol in stored blood. Fluoride, usually at about 1% w/v in forensic kits, inhibits this, preventing falsely raised results.
A hospital reports serum ethanol of 120 mg/dL. The corresponding whole blood ethanol is expected to be:
Serum contains more water than whole blood, so its ethanol concentration is about 1.1-1.2 times higher. Dividing by roughly 1.15 approximates whole blood values, which legal limits usually use.
Most evidential breath alcohol instruments quantify ethanol using:
Ethanol absorbs infrared light at characteristic wavelengths, allowing quantification in breath. Many instruments add an electrochemical fuel cell for specificity. Instruments are calibrated and checked with reference standards.
Before an evidential breath alcohol test, the subject is observed for 15-20 minutes. The main purpose is to:
Recent drinking, vomiting or mouthwash can leave alcohol in the mouth, giving falsely high breath readings. The observation (deprivation) period, with no eating or drinking, removes this effect.
At autopsy, blood ethanol is 90 mg/dL. Which finding best supports that the alcohol was consumed before death?
Vitreous humor is relatively protected from microbial fermentation. A proportionate vitreous ethanol, together with urine ethanol and markers such as EtG, supports antemortem ingestion rather than postmortem production.