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Delayed readings of intradermal drug tests
Why return on day 2–3 and sometimes day 7?
A reaction may appear after you leave: scheduled readings help ensure that a delayed reaction is not missed.
In this sheet
3 essential points
Negative at 20 minutes does not always mean finally negative
The immediate reading mainly looks for rapid reactions. A delayed reaction may appear after 24, 48 or 72 hours, or later.
A hospital reading remains preferable
The doctor assesses more than colour: they also look for elevation, induration and infiltration, and compare the site with the other test points.
Photographs are essential between appointments
A reaction may appear and then fade before your appointment. Photograph it as soon as it appears and record the date and time.
When should I return?
| Time | Why? |
|---|---|
| Day 0 — about 20 minutes | Look for an immediate reaction. |
| Day 2–3 | Look for a delayed reaction. |
| Day 7 if requested by the team | Look for or document a later positive reaction. |
The exact schedule depends on the medicine and your centre’s protocol: a day 7 reading is not routine.
How should I take a good photograph?
If you notice a change, take a photograph immediately, then another a few hours later or the next day if the reaction evolves.
- Good lighting and a sharp image
- Overview of the tested area
- Close-up taken perpendicular to the forearm
- Small ruler next to the reaction
- Keep the site numbers or markings visible
- Keep the photograph’s date and time
Do not decide by yourself that a test is positive: flat redness does not have the same meaning as a red, infiltrated area.
Mini diary after intradermal testing
Record the time, the change observed and whether a photograph was taken for each relevant period.
| Day | What to record |
|---|---|
| Day 0 / day 1 | Time · Change observed · Photograph |
| Day 2 / day 3 | Time · Change observed · Photograph |
| Day 4–7 if needed | Time · Change observed · Photograph |
Key points
An intradermal drug test may be negative on the day of testing and become positive two or three days later. Keep every scheduled reading appointment, monitor the sites until the date given and promptly photograph any change.
Download the validated sheet
Keep this sheet with the reading schedule and instructions provided by your centre.
You may also want to read
Main references
- Barbaud A, et al. Updated EAACI Statement on Drug Hypersensitivity Skin Testing. Allergy. 2026.
- Romano A, et al. EAACI position paper on beta-lactam hypersensitivity. Allergy. 2020.
General information: The instructions and schedule provided by your allergy centre take priority over the general guidance in this sheet.
Scientific review: September 2026 · sosallergo.fr