How to use it
Ask the patient about discharge, pain and restriction of activities, and restriction of sexual activity. Then examine and score the type of perianal disease and the degree of induration. Each item is scored 0–4, for a total of 0–20.
Score what you find today.
Reading the result
| PDAI | What it means |
|---|---|
| 4 or less | Below the activity cut-off |
| More than 4 | Active perianal disease likely (87% accuracy; Losco 2009) |
That single cut-off is the only one that has been validated. There are no validated severity grades and no validated definition of response for the PDAI, so the tool reports the change from baseline in points without labelling it. In Irvine’s original study, when perianal disease improved the PDAI fell by 3.05 ± 2.96 points.
Two situations override a low total:
- Fluctuance or abscess (induration 4). Treat this as possible perianal sepsis. Arrange drainage (examination under anaesthesia, seton if there’s a fistula) and pelvic MRI. ECCO recommends seton drainage before medical or surgical therapy for complex fistulae.
- A fistula that is still draining. Losco’s reference standard counted any visible drainage as active disease.
Clinical closure is not healing
External openings often close before the tract heals. After infliximab, 8 of 11 clinical responders still had active tracks on MRI (Van Assche 2003). Don’t step down therapy on a low PDAI alone; confirm with MRI (or examination under anaesthesia). Current trial recommendations combine clinical and radiological outcomes (Vuyyuru 2026).
Pitfalls
- Skin tags alone score 0 for type of disease.
- Fissures score 1; fewer than 3 fistulae score 2; 3 or more score 3. Ulceration of the sphincter or fistulae with significant undermining of the skin score 4.
- Luminal disease is scored separately. The PDAI says nothing about proctitis; record it with the SES-CD.
- Darvadstrocel (Alofisel) is not an option in practice: it was never marketed in Canada, its EU authorisation was withdrawn in December 2024, and the ADMIRE CD II trial was negative. Mesenchymal stem-cell therapy remains investigational.