Allergy list extraction from records means capturing each allergy a chart documents as one entry with the allergen, the reaction, the severity, the type and the source page. It also means recording "no known allergies" as a positive statement with its own source, so a reader can tell it apart from a chart where nobody recorded allergies at all.
Allergy list fields: allergen, reaction and severity
Allergy list fields describe what the patient reacts to, what happened, how bad it was and where the chart says so. The minimum is the allergen, the reaction, the severity and the source page. Adding a type, a category, a status and a recorded date makes the list much easier to check and merge.
The fields, with outside references
Two published standards give a sensible field set. The USCDI Allergies and Intolerances data class page lists Medication Allergy Intolerance, Drug Class Allergy Intolerance, Non-Medication Allergy Intolerance and Reaction, with RxNorm named for medications and SNOMED CT for drug classes, non-medication substances and reactions. It gives latex, eggs, pollen and peanuts as non-medication examples.
The HL7 FHIR R4 AllergyIntolerance page goes further. Its elements include a clinical status (active, inactive, resolved), a verification status (unconfirmed, confirmed, refuted, entered-in-error), a type (allergy or intolerance), a category (food, medication, environment, biologic), a criticality (low, high, unable-to-assess), and for each reaction a manifestation and a severity of mild, moderate or severe.
A practical layout
| Field | What to record |
|---|---|
| Allergen as written | The exact words on the page |
| Allergen category | Medication, drug class, food, environment or other |
| Reaction as written | The words the chart uses, such as "hives" |
| Severity as written | Only if the chart states it; otherwise "not documented" |
| Type | Allergy, intolerance, or not stated |
| Status | Active, inactive, resolved, or refuted, if stated |
| Source | Document and page |
Record severity only when the chart states it. An extractor who infers severity from the reaction is interpreting clinical content, which belongs to a clinician. The FHIR page also separates severity, which describes a reaction event, from criticality, which it describes as the risk of harm on future exposure. Keep them in separate fields.
Fictional statements and the fields extracted
Every statement, patient and medication name below is invented for this example. The medication names are fictional.
| Statement as written (example) | Allergen | Reaction | Severity | Type | Source |
|---|---|---|---|---|---|
| "Corvaxin: hives, 2019" | Corvaxin | Hives | Not documented | Allergy | Referral letter, p. 2 |
| "Peanuts, throat swelling, severe" | Peanuts | Throat swelling | Severe | Allergy | Intake form, p. 1 |
| "Latex – rash" | Latex | Rash | Not documented | Not stated | Nursing admission note, p. 7 |
| "Brivolate makes her nauseous" | Brivolate | Nausea | Not documented | Intolerance (as stated) | ED note, p. 4 |
| "NKA" | No known allergies | None | None | Negated statement | ED note, p. 4 |
How should "no known allergies" be recorded?
"No known allergies" should be recorded as its own entry, a negated statement with a source page and date, not as an empty list. An empty allergy field could mean the patient has none or that nobody asked. An entry that reads "no known allergies, ED note, page 4" says someone asked and recorded the answer.
The HL7 FHIR AllergyIntolerance page supports this approach. It describes the code element as able to hold a general or categorical negated statement, with "No known allergy" given as an example. That is the same idea in a data standard: absence is recorded as a statement, not as missing data.
The common abbreviations
Charts write this several ways: "NKA" for no known allergies, "NKDA" for no known drug allergies, and sometimes "none" in the allergy box. These are not the same. NKDA covers drugs only, so it does not rule out a food or latex allergy. Record the scope as written. An NKDA entry plus a peanut allergy on another page is not a conflict.
When the list is truly missing
If no document mentions allergies at all, record "allergy status not documented". That is a real finding for a reviewer and very different from a negated statement. Never turn a missing list into "no known allergies".
Allergies versus intolerances and side effects in records
Allergies, intolerances and side effects are different kinds of entries in records, and an extractor should keep the chart's own classification rather than assigning one. Deciding which label fits a patient's reaction is clinical work. The extraction records the label the document uses, or "not stated" when it uses none.
The FHIR page states that "intolerance" should generally apply to a propensity for adverse reactions determined or perceived not to be allergic, and that when it cannot be determined which one a reaction is, the type should be omitted. For extraction, that becomes a simple rule: fill the type only when the chart states it, and leave "not stated" otherwise.
Side effects written in an allergy box are the hardest case. "Brivolate makes her nauseous", in the fictional example above, sits in the allergy section, so it is extracted as an allergy-list entry. The type field records the chart's own words. Whether it is a true allergy is a clinical question, and the extraction does not answer it.
The same page also warns that the type of reaction is not a proxy for seriousness or risk of harm. An entry typed as an intolerance is not less important on paper, and the extraction should not rank it lower.
Where do allergy lists disagree within one record?
Allergy lists disagree within one record most often between an outside referral, the emergency note, the nursing admission note and a patient intake form. One may list a drug the others omit, or one may say NKA while another names an allergen. The extractor records every documented allergy, notes the conflict and sends it to a reviewer.
Typical disagreements
- NKA versus a named allergen. The ED note says NKA, but a referral letter lists Corvaxin. Record Corvaxin, with a note that the ED note disagrees.
- Different reactions. One document says "rash", another says "hives" for the same allergen. Keep one entry with both reactions and both sources.
- Refuted entries. A later note says an old allergy was tested and ruled out. FHIR's verification status includes "refuted" for this. Record the status and its source rather than deleting the entry.
- Intake form versus clinician note. A patient may list an allergy on an intake form that never reaches the clinician's note. Intake paperwork has its own field patterns, covered in the patient intake category.
Keep the sources together
Each merged entry should keep every source page, so a reviewer sees all the evidence in one place. The same habit applies to the other lists in a chart, such as problem list extraction from charts, and to measurements like weight and blood pressure in vital signs extraction from scanned charts.
Allergies are one of the medical record fields Schema Care reads, alongside encounter dates, problem lists and vitals; each comes back with a confidence score and its spot on the page, and the full set is listed under the documents Schema Care reads.