3.8 Toxicology

Many kinds of test methods are used in toxicology:

• Screening tests include HPLC, EIA, TLC, RIA, GC, and GCMS (rarely).
• Confirmation tests are GCMS, LCMS, GC, and HPLC.

The following table indicates Drug of Abuse Methods.

Many laboratories use GCMS to signal that the test is a confirmation of a previous screening test, but other methods are also used to confirm, and a given method can be used to screen or to confirm a test. However, it is important that two different methods be used for screen and for confirm and that they both be applied with techniques appropriate to the mode (screen or confirm). So the LOINC committee has determined it is better to distinguish the screening from the confirming procedure by the use of the words screen or confirm, in the Method part of the name, rather than by naming a specific method. Hence LOINC will distinguish toxicology Method by Screen and Confirm but not by particular methods.

Toxicology tests can also be performed on a group of drugs/substances or on individual drugs/metabolites/substances. We will develop LOINC names and codes for both categories: groups of analytes, e.g., “barbiturates”, and individual analytes, e.g., “phenobarbital.”

Group test results are usually reported as ordinal (present /absent) but can also be reported as mass concentrations when the numerator is the total mass of the detectable substances in the group. Group tests at the screening level may also be followed by a confirmation at the group level or by confirms of the individual drug/substance tests at the confirmatory level. Individual drugs/substances may be reported as present/absent (Ord) or as mass (or substance) concentrations (Qn).

When individual drugs/substances are reported ordinally, the reporting threshold (the threshold at which a test level is considered positive) may also be reported as a separate “result.” Thus we have separate LOINC codes to report the cutoff used for defining a positive or negative value.

3.8.1 Toxicology drug groups

General principles: for each “group” of drugs (amphetamines, benzodiazepines, opiates, etc.) we will define the following kinds of LOINC observations:

3.8.1.1 Screen for a group of drugs/ toxic substances

Terms representing screening for the group as a whole:

“X”:PrThr:Pt:Ord:{System}:Screen

Example answers: present/absent

For example,

Amphetamines:PrThr:Pt:Urine:Ord:Screen

Answer: present

Terms to identify the set of drugs/substances screened for by the group test. Here the answer will be a list of discrete drug/substance names or codes:

“X” tested for:Prid:Pt:{System}:Nom:Screen

Example answers: individual drugs that this screening test could detect, from a fixed list

For example,

Amphetamines tested for:Prid:Pt:Urine:Nom:Screen

Answer: amphetamine, methamphetamine, dextroamphetamine, levoamphetamine, pseudoephedrine

3.8.1.2 Identify the drugs or substances screened for (and perhaps other information) as narrative

Terms of this format carry answers that are reported as a “glob” of narrative text. When a screen is reported as negative, confirmatory testing is not performed. When a screening test is reported as positive, the result must be confirmed by an independent testing method.

“X” tested for:Prid:Pt:{System}:Nar:Screen

Example answers: individual drugs that this screening test could detect, reported as a “blob” of text or canned comment.

For example,

Amphetamines tested for:Prid:Pt:Urine:Nar:Screen

Answer: The EMIT urine screen for amphetamines detects amphetamine, methamphetamine, dextroamphetamine, levoamphetamine as indications of methamphetamine abuse. It is also reactive with a component present in over-the-counter nasal decongestant inhalers, and a positive result must be confirmed by a quantitative method that rules out the non-abuse situation.

3.8.1.3 Confirmatory testing for the presence of one or more members of the group represented as a single observation

“X”:PrThr:Pt:{System}:Ord:Confirm

Example answers: present/absent

For example,

Amphetamines:PrThr:Pt:Urine:Ord:Confirm

Answer: present

3.8.1.4 List of the actual drug/substances confirmed

“X” positive:Prid:Pt:{System}:Nom:Confirm

Example answers: a list of analytes detected

For example,

Amphetamines positive:Prid:Pt:Urine:Nom:Confirm

Answer: dextroamphetamine, methamphetamine

3.8.1.5 Confirmatory testing reported as a set of observations (more common)

More commonly, confirmatory testing is reported as a set of observations that each report the presence (or quantitative amount detected) of an analyte in the group.

“X”:PrThr:Pt:{System}:Ord:Confirm

Example answers: present/absent

or

“X”:MCnc:Pt:{System}:Qn:Confirm

Example answers: a quantitative amount

For example,

Amphetamine:PrThr:Pt:Urine:Ord:Confirm

Dextroamphetamine:PrThr:Pt:Urine:Ord:Confirm

Methamphetamine:PrThr:Pt:Urine:Ord:Confirm

Levomethamphetamine:PrThr:Pt:Urine:Ord:Confirm

Example answers: present/absent

3.8.2 Cutoffs

The cutoff levels for screens and confirms of a given substance or group of substances will usually differ. There are three ways to indicate specific cutoffs in LOINC.

3.8.2.1 We provide separate LOINC terms for reporting the cutoff levels of a number of commonly abused substances and substance groups

“X” cutoff:MCnc:Pt:Urine:Qn:Screen
“X” cutoff:MCnc:Pt:Urine:Qn:Confirm

For example,

Amphetamines cutoff:MCnc:Pt:Urine:Qn:Screen

Answer: 1000 ng/ml

Methamphetamine cutoff:MCnc:Pt:Urine:Qn:Confirm

Answer: 500 ng/ml

3.8.2.2 Two general cutoff terms, one for screen and one for confirm, can be applied to any substance whether or not a pre-coordinated term exists

"X" cutoff:MCnc:Pt:{System}:Qn:Screen
"X" cutoff:MCnc:Pt:{System}:Qn:Confirm

3.8.2.3 For commonly used cutoffs, such as those mandated by regulatory agencies, we provide pre-coordinated terms for reporting a “present/absent” result with the cutoff specified in the Method field

“X”:PrThr:Pt:{System}:Ord:Screen>“N”
“X”:PrThr:Pt:{System}:Ord:Confirm>“N”

For example,

Amphetamines:PrThr:Pt:Urine:Ord:Screen>1000 ng/mL

Answer: not detected

3.8.3 Reporting the Method used for screen and confirm

We provide terms for reporting the Method used for screen and confirm tests:

“X” screen method:Prid:Pt:{System}:Nom:*
“X” confirm method:Prid:Pt:{System}:Nom:*

These would normally be reported in conjunction with terms reporting levels and possibly cutoffs, as in the following example:

Amphetamines:PrThr:Pt:Urine:Ord:Confirm

Answer: positive

Amphetamines cutoff:MCnc:Pt:Urine:Qn:Screen

Answer: 1000 ng/ml

Amphetamines screen method:Prid:Pt:Urine:Nom:*

Answer: EIA

Amphetamines positive:Prid:Pt:Urine:Nom:Confirm

Answer: amphetamine, methamphetamine

Amphetamine cutoff:MCnc:Pt:Urine:Qn:Confirm

Answer: 500 ng/ml

Methamphetamine cutoff:MCnc:Pt:Urine:Qn:Confirm

Answer: 500 ng/ml

Amphetamines confirm method:Prid:Pt:Urine:Nom:*

Answer: GC/MS

3.8.4 Individual drug/metabolite test results

Individual substances are typically reported as screens (ordinal), confirms (ordinal) or confirms (quantitative – usually mass or substance concentrations), though some labs also report as screen (quantitative). Ordinal terms for reporting individual substances should always specify a Method of screen or confirm.

Group test screens may be confirmed by group confirms (as described above) or by individual confirms (Either ordinal or quantitative-depending upon the laboratory’s preference).

3.8.4.1 Individual test screen (ordinal)

Methamphetamine:PrThr:Pt:Urine:Ord:Screen

Example answer: present

3.8.4.2 Individual test screen (quantitative)

Methadone:MCnc:Pt:Urine:Qn:Screen

Example answer: 150 ng/ml

3.8.4.3 Individual test confirm (ordinal)

Methamphetamine:PrThr:Pt:Urine:Ord:Confirm

Example answer: present

3.8.4.4 Individual test confirm (quantitative)

Methamphetamine:MCnc:Pt:Urine:Qn:Confirm

Example answer: 250 ng/ml

Individual tests may also be reported as simple quantitative (without confirm or screen), as is the case for therapeutic drug level monitoring.

3.8.4.5 Individual substance measured quantitatively; screen/confirm is not relevant

Digoxin:MCnc:Pt:Ser/Plas:Qn:

Example answer: 1.2 ng/ml

3.8.5 Naming issues

For confirms, you would always be looking for specific analytes. For example, you would never look for tetrahydrocannabinol, but would look for delta-9-tetrahydrocannabinol, 11-hydroxycannabinol, etc.

3.8.6 Summary

For each “group” LOINC defines the following set of terms:

“Analyte group”:PrThr:Pt:Urine:Ord:Screen
“Analyte group”:PrThr:Pt:Urine:Ord:Confirm
“Analyte group”:MCnc:Pt:Urine:Qn:Confirm
“Analyte group” tested for:Prid:Pt:Urine:Nom:Screen
“Analyte group” tested for:Prid:Pt:Urine:Nar:Screen
“Analyte group” positive:Prid:Pt:Urine:Nom:Confirm
“Analyte group” screen method:Prid:Pt:Urine:Nom:*
“Analyte group” confirm method:Prid:Pt:Urine:Nom:*

For each individual analyte LOINC now defines the following set of terms:

Analyte:PrThr:Pt:Urine:Ord:Screen
Analyte:PrThr:Pt:Urine:Ord:Confirm
Analyte:MCnc:Pt:Urine:Qn:Confirm
Analyte:MCnc:Pt:Urine:Qn:
Analyte cutoff:MCnc:Pt:Urine:Qn:Screen
Analyte cutoff:MCnc:Pt:Urine:Qn:Confirm