Table 2.

Examples of toxicology laboratory investigations according to tier.

Tier	Description	Examples	Turnaround time
Tier 1	Essential tests recommended for ready availability in all hospital EDs Findings often have urgent implications for patient management	Quantitative tests • Acetaminophen • Carbamazepine • Co-oximetry* • Digoxin • Ethanol • Ethylene glycol • Iron • Lithium • Methanol • Methotrexate • Phenobarbital • Salicylates • Theophylline • Valproic acid	1–4 h
Tier 2	Additional or specialized investigations that require advanced equipment or processes Findings are typically confirmative or provide additional information but do not tend to guide immediate management	• Heavy metals • Drug of abuse screening • Unknown drug screening with confirmatory tests • Pseudocholinesterase	24 h or longer

Abbreviation: ED = emergency department.

*To determine oxygen saturation, carboxyhemoglobin, and methemoglobin.