Asthma and lower airway disease
Validation of the Asthma Predictive Index and comparison with simpler clinical prediction rules

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Background

The loose and stringent Asthma Predictive Indices (API), developed in Tucson, are popular rules to predict asthma in preschool children. To be clinically useful, they require validation in different settings.

Objective

To assess the predictive performance of the API in an independent population and compare it with simpler rules based only on preschool wheeze.

Methods

We studied 1954 children of the population-based Leicester Respiratory Cohort, followed up from age 1 to 10 years. The API and frequency of wheeze were assessed at age 3 years, and we determined their association with asthma at ages 7 and 10 years by using logistic regression. We computed test characteristics and measures of predictive performance to validate the API and compare it with simpler rules.

Results

The ability of the API to predict asthma in Leicester was comparable to Tucson: for the loose API, odds ratios for asthma at age 7 years were 5.2 in Leicester (5.5 in Tucson), and positive predictive values were 26% (26%). For the stringent API, these values were 8.2 (9.8) and 40% (48%). For the simpler rule early wheeze, corresponding values were 5.4 and 21%; for early frequent wheeze, 6.7 and 36%. The discriminative ability of all prediction rules was moderate (c statistic ≤ 0.7) and overall predictive performance low (scaled Brier score < 20%).

Conclusion

Predictive performance of the API in Leicester, although comparable to the original study, was modest and similar to prediction based only on preschool wheeze. This highlights the need for better prediction rules.

Section snippets

Development cohort

The TCRS, a birth cohort study in Arizona, contacted 1596 healthy infants between 1980 and 1984.23 Baseline clinical information for the API was assessed from questionnaires at enrollment and at ages 2 and 3 years and from a blood sample at age 1 year; the outcome asthma was assessed at ages 6, 8, 11, and 13 years (Table I).1, 24

Validation cohort

The Leicester 1998b Respiratory Cohort (LRC, www.leicestercohorts.org) is a population-based stratified random sample of children recruited in 1998 at the age of 1 year

Study populations

The TCRS and LRC are large, unselected, mixed-ethnicity prospective cohorts with comparable sex balances and ages at follow-ups (Table I). Children in LRC were recruited ∼15 years later, live in a different climate zone, and provided no blood sample.

In LRC, 3392 of 4300 invited children replied to the first postal questionnaire, and 2948 provided enough information at baseline to determine the API, of whom 1954 also provided information on asthma at 7 or 10 years. These children did not differ

Discussion

We found that the API developed in Tucson predicted asthma at school age in Leicestershire similarly, despite disparities in location, recruitment period, and predictor variables. This supports the generalizability of the API to other settings. Its predictive accuracy, however, was modest, and simpler rules based only on frequency of preschool wheeze showed comparable performance, suggesting that the additional criteria included in the API—1 of them requiring a blood sample—do not improve

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  • Cited by (0)

    Supported by the Swiss National Science Foundation (PDFMP3-123162, 823B-046481, 3200B0-122341) and Asthma UK (07/048).

    Disclosure of potential conflict of interest: The authors have declared that they have no conflict of interest.

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