Forensic Science: Alcohol & drug testing – page 2

Sustained heavy drinking reduces transferrin glycosylation, increasing CDT. It normalizes over two to four weeks of abstinence and is more specific than gamma-glutamyl transferase.

A cutoff is an administrative threshold. A negative result does not mean zero drug, only that any drug present was below the cutoff; results at or above it are non-negative.

The initial immunoassay cutoff for marijuana metabolites is 50 ng/mL, and positives are confirmed by mass spectrometry for THC-COOH at 15 ng/mL. The lower confirmatory cutoff targets one specific analyte.

The 2017 federal guidelines set 150 ng/mL for the initial cocaine metabolite immunoassay and 100 ng/mL for benzoylecgonine confirmation. The earlier 300 ng/mL initial cutoff was lowered in 2010.

The specimen is divided into Bottle A for primary testing and Bottle B, sealed and stored. If Bottle A is verified positive, adulterated or substituted, the donor may request Bottle B testing at a different certified laboratory.

A dilute specimen has creatinine of at least 2 but below 20 mg/dL and specific gravity above 1.0010 but below 1.0030. It is reported with the drug result; the MRO or employer may order recollection.

Nitrite at or above 500 micrograms/mL indicates addition of an oxidizing adulterant, which can destroy THC-COOH and other analytes. Such concentrations are not found in normal or infected urine.

Physiological urine pH is roughly 4.5-9. A pH below 4 or at or above 11 indicates an added acid or base, and the specimen is reported as adulterated.

Poppy seeds contain morphine and codeine, and eating them can produce urinary morphine above 300 ng/mL. The 2000 ng/mL cutoff reduces such positives, while 6-acetylmorphine testing detects heroin.

Oral fluid is collected under direct observation without privacy concerns, reducing opportunity for tampering. It detects mainly recent use, generally hours to a day or two.

A confirmation breath alcohol of 0.04 or higher is a violation; the employee is removed from safety-sensitive functions and cannot return without evaluation. Results of 0.02-0.039 require temporary removal.

Ethanol distributes in body water. On average women have more body fat and less water per kilogram, so the same dose gives a higher blood concentration, reflected by a lower r value.

Alcohol dehydrogenase oxidizes ethanol while reducing NAD+ to NADH. NADH absorbs at 340 nm, so the rise in absorbance is proportional to the ethanol concentration.

Lactate dehydrogenase converts lactate to pyruvate while reducing NAD+ to NADH, mimicking the ethanol reaction. Elevated lactate and LDH are common after death or in shock, so GC confirmation is preferred.

EtG is a minor direct metabolite of ethanol excreted in urine for up to about 3-5 days after drinking. Incidental exposure, like hand sanitizers, may give low positives, so cutoffs matter.

PEth forms in red cell membranes only in the presence of ethanol and has a half-life of several days. It reflects drinking over recent weeks and distinguishes heavy from light use.

Creatinine below 2 mg/dL with specific gravity at or below 1.0010, or at or above 1.0200, is inconsistent with human urine. The specimen is considered substituted, for example with water.

THC in oral fluid largely comes from local deposition during smoking or oral intake, so parent THC is the target and indicates recent use. Urine testing instead targets the metabolite THC-COOH.

Back-calculation assumes a known, constant elimination rate after absorption is complete. If absorption was ongoing, the earlier concentration could have been lower, so the extrapolation would be invalid.

Yeast such as Candida can ferment glucose to ethanol in unpreserved urine. EtG is formed only in the body after drinking, so its absence with ethanol present points to post-collection production.