HL7 v2 AL1-2 Field Guide: Allergen Type Code Values and Common Mistakes
AL1-2 decides which bucket an allergy falls into before anyone even looks at what the allergy actually is. Get this field wrong in test data and you end up validating only the drug-allergy code path while food, environmental, and latex allergies quietly go untested.
AL1-2 is a coded field that classifies the type of allergy being reported: drug, food, environmental, latex, animal, plant, or miscellaneous. Systems often use this code to route the allergy toward different alerting or display logic, which makes it worth testing across every value, not just the common ones.
Valid code values
Example
AL1-2 carries "DA", classifying this as a drug allergy.
Where this trips people up
Test suites built from a handful of hand-copied sample messages almost always skew toward "DA" because that is the example everyone remembers. If your synthetic data never includes FA, EA, LA, AA, or PA, you will not find out until production that your allergy-display component only styles drug allergies correctly, or that your alerting rules silently ignore food allergies because nobody ever fed one through the pipeline. It is also worth testing an unrecognized or unmapped code value, since some interfaces fail closed and others fail open when they hit a type code they do not recognize.