Acetaminophen, plasma or serum

Alternate test name

Tylenol, Paracetamol

Lab area

Clinical Biochemistry - TDM & Toxicology

Method and equipment

Equipment : Roche Cobas Pro c503

Method : The assay is based on a homogeneous enzyme immunoassay technique
used for the quantitative analysis of acetaminophen in human serum or
plasma. The assay is based on competition between drug in the sample
and drug labeled with the enzyme glucose‑6‑phosphate dehydrogenase
(G6PDH) for antibody binding sites. Enzyme activity decreases upon
binding to the antibody, so the drug concentration in the sample can be
measured in terms of enzyme activity. Active enzyme converts oxidized
nicotinamide adenine dinucleotide (NAD+) to NADH, resulting in an
absorbance change that is measured spectrophotometrically. Endogenous
serum G6PDH does not interfere because the coenzyme functions only with
the bacterial (Leuconostoc mesenteroides) enzyme employed in the assay.

Expected turn-around time

STAT/ Urgent/ Routine: 3 hours

Specimen type

Serum, Plasma (Heparin)

Specimen requirements

150 uL

Storage and transportation

Shipping information

The Hospital for Sick Children

Rapid Response Laboratory

555 University Avenue, Room 3642

Toronto, ON

Canada

M5G 1X8

Phone: 416-813-7200

Toll Free: 1-855-381-3212

Hours: 7 days/week, 24 hours/day

Requisition

Acetaminophen, plasma or serum - requisition

Background and clinical significance

Acetaminophen is one of the most widely used analgesics on the market today. It is available in many formulations including liquid, tablets, capsules and suppositories. The chemical name is N-acetyl-p-aminophenol (APAP). Acetaminophen has an excellent safety profile in therapeutic doses, but hepatotoxicty can develop in overdose situations. Metabolism is primarily hepatic with the half life being 2 to 4 hours. The parent compound, acetaminophen is non-toxic, but the metabolite N-acetyl-benzoquinoneimine (NAPQI) is toxic. Normally, glutathione will bind the NAPQI and form a non-toxic conjugate which is excreted. In overdose situations, as glutatione stores are depleted, the NAPQI binds to the lipid bilayer of the hepatocytes resulting in necrosis. N-acetylcysteine (NAC) is an effective antidote.