HL7 Table HL70127: Allergen Type

HL70127 is the HL7-defined code table that classifies the broad category of an allergen recorded on a patient. It is the binding for AL1-2 Allergen Type Code on legacy ADT-based allergy reporting and for IAM-2 Allergen Type Code on modern patient-allergy IAM segments. The codes describe the kind of substance (drug, food, environmental) rather than the specific allergen — the specific allergen lives in AL1-3 / IAM-3.

Purpose

HL70127 lets receiving systems route, alert, and de-duplicate allergies by class without parsing the specific allergen string. A pharmacy module that only cares about drug allergies can filter on DA; a dietary module filters on FA; an environmental-controls module on EA or LA. The category is independent of severity (HL70128) and clinical status (HL70438) — those are carried on separate fields.

Because HL70127 is HL7-defined, every conformant v2 receiver is expected to recognize all eight codes without local extension. Sites that need a richer ontology (latex, contrast media, insect venom) carry that distinction on the specific-allergen field (AL1-3 / IAM-3) coded against SNOMED CT or RxNorm, rather than coining new HL70127 codes.

Where it's used

AL1-2 Allergen Type Code — the legacy ADT allergy segment; still widely emitted by older registration systems.
IAM-2 Allergen Type Code — the modern patient-allergy segment introduced in v2.4 and preferred from v2.5 onward.
Some site-defined PRT (Participation) profiles that need to flag the allergen class of an exposure during a procedure.

Code list

Code	Display	Comment/Description
AA	Animal Allergy	Allergy to animal dander, fur, or saliva (cat, dog, horse, etc.).
DA	Drug Allergy	Allergy to a pharmaceutical agent — the most common category in inpatient settings.
EA	Environmental Allergy	Allergy to environmental substances (dust mite, mold, smoke). Distinct from pollen (LA) and animal (AA).
FA	Food Allergy	Allergy to a food substance (peanut, shellfish, dairy).
LA	Pollen Allergy	Allergy to plant pollen — the abbreviation reflects the historical Latin term "lentigo/pollen"; modern profiles often call this Pollen Allergy explicitly.
MA	Miscellaneous Allergy	Allergy that does not fit AA, DA, EA, FA, LA, or PA — used sparingly.
MC	Miscellaneous Contraindication	A non-allergic contraindication (for example, a drug-drug interaction recorded on the allergy segment for routing convenience).
PA	Plant Allergy	Allergy to a non-pollen plant substance (poison ivy, latex sap).

Code system OID

OID: 2.16.840.1.113883.18.49
Canonical URI: http://terminology.hl7.org/CodeSystem/v2-0127

The OID resolves on the HL7 Terminology server and is the value Vorro emits in CWE.14 when a downstream profile demands OID-bound coded values for AL1-2 or IAM-2.

HL7-defined vs user-defined

HL70127 is HL7-defined. The table number falls inside the HL7-reserved range (HL70001–HL70999) and the code set is normative — receivers must accept all eight values without local extension, and senders must not invent additional codes inside this table. Sites that need richer allergen-class semantics carry that on the specific-allergen field (AL1-3 / IAM-3) bound to SNOMED CT or RxNorm rather than extending HL70127.

Version differences

v2.1 – v2.2 — Initial three values: DA, FA, MA. Sufficient for the original AL1 use case (inpatient drug-allergy alerts).
v2.3 — EA (Environmental Allergy), AA (Animal Allergy), PA (Plant Allergy), LA (Pollen Allergy) added to accommodate outpatient and primary-care allergy reporting.
v2.3.1 — MC (Miscellaneous Contraindication) added so non-allergic contraindications could ride on the allergy segment without misuse of MA.
v2.4 – v2.8.1 — Set frozen at eight codes; the IAM segment supersedes AL1 but the table is unchanged.
v2.9 — Table unchanged. FHIR mapping clarified in the v2-to-FHIR IG to handle the lossy collapse onto AllergyIntolerance.category.

Common mistakes

Using MA as a default when the source EHR does not categorize the allergen. MA means "miscellaneous" — a deliberate "none of the above" — not "unknown." Unknown classifications should be carried as null and routed to curation.
Treating DA as the only legal value because the pharmacy is the only downstream consumer. Allergy segments are routed to dietary and clinical-decision-support modules too; mis-classifying a peanut allergy as DA blocks the dietary alert.
Confusing EA (Environmental) with LA (Pollen). Pollen is a specific subset of environmental allergens and has its own code; sending pollen allergies as EA defeats the routing purpose of the table.
Putting drug-drug interactions on AL1 with DA. A drug-drug interaction is a contraindication, not an allergy; the correct code is MC.
Extending HL70127 locally with LX for latex or CM for contrast media. HL70127 is HL7-defined; the latex or contrast-media specificity belongs in AL1-3 / IAM-3 against SNOMED CT.

Examples

A minimal AL1 reporting a penicillin drug allergy:

AL1|1|DA|7980^Penicillin^RXNORM|SV|Hives|20240101

A peanut food allergy on a modern IAM segment:

IAM|1||DA^Drug Allergy^HL70127|7980^Penicillin^RXNORM|SV^Severe^HL70128|||||C^Confirmed^HL70438
IAM|2||FA^Food Allergy^HL70127|762952008^Peanut^SCT|MO^Moderate^HL70128|||||C^Confirmed^HL70438

A drug-drug contraindication recorded as MC:

IAM|3||MC^Miscellaneous Contraindication^HL70127|warfarin-aspirin^Warfarin/Aspirin interaction^L||||||C^Confirmed^HL70438

Same penicillin DA translated to a FHIR AllergyIntolerance snippet:

{
  "resourceType": "AllergyIntolerance",
  "id": "ai-10456-pen",
  "category": ["medication"],
  "code": {
    "coding": [{
      "system": "http://www.nlm.nih.gov/research/umls/rxnorm",
      "code": "7980",
      "display": "Penicillin"
    }]
  },
  "patient": {"reference": "Patient/10456"}
}

Mapping failure example — unknown vendor code:

IAM|1||LX^Latex Allergy^L|111088007^Latex^SCT|MO^Moderate^HL70128

LX is not in HL70127. A conformant engine should route the message to a curation queue, recognize that latex belongs in PA (Plant Allergy) with the SNOMED specificity preserved in IAM-3, and create a remap rule rather than silently dropping the allergy.

FHIR mapping

The HL7 v2-to-FHIR Implementation Guide publishes ConceptMap-table-hl70127-to-allergy-intolerance-category, which collapses HL70127's eight codes onto the four-value FHIR AllergyIntolerance.category value set:

HL7 v2 (HL70127)	FHIR (AllergyIntolerance.category)	Notes
DA	medication	Direct match.
FA	food	Direct match.
EA	environment	Direct match.
LA	environment	Lossy — pollen specificity preserved as extension.
AA	environment	Lossy — animal specificity preserved as extension.
PA	environment	Lossy — plant specificity preserved as extension.
MA	(null)	No FHIR equivalent; preserved on `AllergyIntolerance.code` text.
MC	(null)	Not an allergy in FHIR; modeled as `DetectedIssue` or `Flag` instead.

AllergyIntolerance.category is a code repeating element bound to http://hl7.org/fhir/ValueSet/allergy-intolerance-category. Because four v2 codes (EA, LA, AA, PA) collapse to FHIR environment, the original HL70127 code must be preserved as an extension if the receiver needs to round-trip back to HL7 v2.

Engine considerations

Two-character validation — AL1-2 / IAM-2 codes are exactly two characters; reject longer payloads.
Case sensitivity — HL70127 codes are uppercase; da is not valid. Normalize on ingest.
CWE upgrade path — In v2.7+ profiles IAM-2 is CWE with OID metadata in CWE.14 (2.16.840.1.113883.18.49). Engines must handle both IS and CWE shapes.
Round-trip preservation — When mapping LA/AA/PA to FHIR environment, always store the original HL70127 code as an extension so the outbound v2 channel can restore the specific category.
MC routing — MC is not an allergy. Engines should emit MC as a FHIR DetectedIssue rather than an AllergyIntolerance, and downstream consumers must be wired accordingly.

How Vorro handles HL70127

Vorro validates AL1-2 and IAM-2 against the eight HL70127 codes on ingest. Values that match are forwarded to all downstream channels untouched. Values that fail validation — including lowercase variants, common vendor extensions like LX for latex, and accidental display strings — are routed to the terminology curation queue, where they either resolve to one of the eight canonical codes (with the specific allergen preserved in IAM-3 against SNOMED) or pass through with a soft warning.

On outbound to FHIR, Vorro emits the IG-recommended AllergyIntolerance.category value and attaches the original HL70127 code as an extension so round-trip back to v2 is lossless. MC is routed to a DetectedIssue resource rather than AllergyIntolerance. Vorro also enforces the "DA requires an RxNorm code in IAM-3" guard so downstream pharmacy systems never receive an uncoded drug allergy.

Sources

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