Review
Predicting persistence of asthma in preschool wheezers: crystal balls or muddy waters?

https://doi.org/10.1016/j.prrv.2012.08.004Get rights and content

Summary

Since preschool wheezing is the common expression of several heterogeneous disorders, identification of children at risk for persistent asthma is particularly challenging. To date, efforts to predict the outcome of preschool wheeze have mainly relied on predictive rules consisting of simple clinical and laboratory parameters. Among these tools, the asthma predictive index (API) has been introduced in international guidelines and position papers and is recommended for use in clinical practice. This article reviews the currently available asthma predictive models focusing on their validity and performance characteristics. Although these tools are generally simple and easy to apply, they suffer important intrinsic and practical limitations and they have been insufficiently validated to allow for widespread use in clinical settings. We also present evidence that their ability to predict the long-term outcome of preschool wheeze is limited in general populations, and even poorer in high-risk children in which prediction of asthma persistence might have important clinical and prognostic implications. Due to the complex and multifactorial nature of asthma, prediction of asthma persistence based on simple clinical models is practically impossible.

Section snippets

Background

Preschool wheezing is the common expression of several heterogeneous disorders with variable course and prognosis.1 During the first years of life, approximately one third of children will have at least one episode of wheeze, and in half of these children the symptoms will be recurrent.2 However, although these episodes resemble asthma exacerbations in older children, approximately two-thirds of preschool wheezers cease to wheeze by the age of 6 years.2 Therefore, identification of symptomatic

Currently available asthma predictive models

API. The API was developed in 2000 by Castro-Rodríguez et al.25 The investigators used data from 1,246 children in the Tuscon Children's Respiratory Study cohort to identify clinical and laboratory parameters in recurrent wheezers during the first 3 years of life, which could predict asthma persistence beyond the age of 6 years. In combination with the number of wheezing episodes, these parameters (named “criteria”) were used to create two predictive indices: a loose and a stringent API. These

General principles

As a basic rule in clinical epidemiology, a predictive rule developed in any given population should be applied in practice only after it has been validated in a different cohort; this is termed “broad” or “level 2” validation.43 Conversely, “narrow” validation refers to the evaluation of the model either within the sample it was derived from (“level 4” validation) or in a different cohort with similar characteristics (“level 3” validation).43 This preliminary “narrow” validation process

Limitations

Besides their poor performance in validation studies (if at all available), asthma predictive models also present important limitations related to their development methodology and clinical applicability.

In the case of API, it remains unclear exactly how the cut-off point between loose and stringent API (< 3 or > 3 wheezing episodes) was derived. In the original study, parents rated the frequency of wheezing using a Likert-type scale from 1 (“very rarely”) to 5 (“on most days”),25 but it was

Discussion

Successful introduction of a predictive rule in clinical practice is dependent on its simplicity, performance characteristics, and clinical and prognostic implications. Moreover, the clinical usefulness of a predictive tool depends strongly on the aim of the prediction per se. In general paediatric practice, for example, clinicians caring for wheezing preschoolers seek to identify children at risk for later asthma and to decide with sufficient certainty whether they should intervene. In

Conclusions

The available asthma predictive models suffer important intrinsic and practical limitations, precluding their useful clinical applicability. Although these tools are generally simple and easy to apply, they have been insufficiently validated, and they have limited predictive value in terms of confirming or ruling out persistence of asthma symptoms among preschool wheezers. The stringent API in particular performs poorly in high-risk populations in which early identification of children at risk

Educational aims

After reading this article the reader will be able to:

  • •

    Describe the currently available asthma predictive models (such as the asthma predictive index, API) and understand the rationale for their development.

  • •

    Describe the methodological and practical limitations of the available asthma predictive models.

  • •

    Understand the poor ability of the available asthma predictive models to predict the long-term outcome of preschool wheeze.

Future directions

Future research on asthma predictive models should include:

  • •

    Proper validation in independent populations and clinical settings.

  • •

    Assessment of their performance by longitudinal follow-up of high-risk cohorts.

  • •

    Assessment of their true clinical impact.

  • •

    Development of more accurate models by identifying and incorporating new predictive variables

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