What it is
The Asthma Predictive Index (API), derived by Castro-Rodriguez from the Tucson Children’s Respiratory Study cohort, estimates the risk that a wheezing preschooler will have active asthma at school age. It is a prognostic tool, not a diagnosis: it combines a recurrent wheeze gate with a small set of atopy-related criteria.
How it scores
The API is positive when a child with recurrent early wheezing also meets ≥1 major criterion OR ≥2 minor criteria.
Major criteria (need ≥1):
- Parental asthma (physician-diagnosed)
- Physician-diagnosed atopic dermatitis (eczema)
Minor criteria (need ≥2):
- Physician-diagnosed allergic rhinitis
- Wheezing apart from colds
- Blood eosinophilia ≥4%
Stringent vs loose
The two forms differ only in the wheeze-frequency gate:
- Stringent — frequent wheeze (≥3 episodes/year in the first 3 years) plus the criteria above.
- Loose — infrequent wheeze (≥1 episode/year) plus the criteria above.
A positive stringent API carries a markedly higher risk of active asthma at school age. The chief value of the index is its high negative predictive value — a negative API makes future asthma unlikely.
When to use it
In a wheezing child under roughly 3 years of age, to counsel families on prognosis and to inform decisions about controller therapy and follow-up. It is best read as a risk discussion, not a gatekeeper to treatment.
Worked example
A 2-year-old with four wheeze episodes in the past year (stringent gate met), no parental asthma, no eczema (majors 0/2), but physician-diagnosed allergic rhinitis (+minor), wheezing between colds (+minor) and eosinophils 5% (+minor) → minors 3/3.
Majors 0, minors ≥2 → Positive (stringent). High risk of asthma at school age; warrants close follow-up.
Pitfalls
- Recurrent wheeze is a prerequisite — the criteria alone, without a wheeze history, do not make a positive index.
- This is the original API. The modified API (mAPI, Guilbert 2004) promotes eosinophilia ≥4% to a major criterion and adds aeroallergen/food sensitisation — do not mix definitions.
- Eosinophilia is a percentage (≥4%), not an absolute count.
- A positive API predicts risk, not certainty; a negative API is reassuring but not absolute.
Run it: Asthma Predictive Index (API)
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.