Screening tool for predicting asthma in children

DIAGNOSING asthma in young children is notoriously difficult. There is currently no single gold standard test for definitively confirming asthma in adults, let alone in children.

Asthma diagnosis is largely based on clinical judgement of the patient’s medical history, symptoms, and objective measures of airflow obstruction. These objective measures, which include lung function tests, are tricky to obtain in young children under the age of 6 years.

Furthermore, wheeze, a key symptom of asthma, is very common in babies and toddlers.

Because of the high occurrence of wheeze in young children, the Australian Asthma Handbook does not recommend children under 12 months to be diagnosed with asthma. Currently, a provisional diagnosis of asthma in children under 6 years involves a trial-and-error approach of responsiveness to a reliever or preventer. As a result, due to the challenges in diagnosing asthma in young children, clinicians may be hesitant to provide a formal diagnosis.

There has been no lack of efforts to develop prediction tools for childhood asthma. The advantages of an early diagnosis of asthma are that it would allow for interventions to control asthma symptoms in children who are most likely to benefit and would limit prescribing asthma medications for children with transient wheeze who are unlikely to respond to treatment.

One of the most well known tools for predicting asthma in children is the Asthma Predictive Index (API) and it’s modified version (mAPI). Unfortunately, although these tools can predict children at high risk of asthma, they have higher negative predictive values than positive predictive values, meaning they are better at ruling out asthma rather than confirming a diagnosis with certainty.

Furthermore, the API and other similar predictive indexes require invasive skin prick tests and blood sampling to be undertaken. These tests, with the use of needles or lancets, are unpleasant for young children and clinic visits often end in tears.

Given that gaps still exist in the asthma prediction space, we and our colleagues at the Hospital for Sick Children (SickKids) in Toronto used data from a Canada-wide birth cohort study to develop the CHILDhood Asthma Risk Tool (CHART).

CHART is a simple screening tool that can be used in children as young as 2 years to determine those who would go on to have persistent symptoms or asthma at 5 years through asking just five questions on symptoms, asthma medication use, and emergency department visits.

Essentially, if a young child experienced more than two wheezing episodes in the past 12 months in combination with either an emergency department or hospital visit for asthma symptoms, use of asthma medications or cough without a cold, they were considered as high risk.

CHART had a sensitivity of 91% of identifying children at high risk or persistent wheeze compared with physician diagnoses and the mAPI, which had sensitivities of 62% and 49% respectively.

It might seem too good to be true that the use of symptom or medical history questions alone may be effective in predicting persistent asthma symptoms. However, this makes sense when considering that it is really recurring symptoms, medications to relieve said symptoms, and emergency department visits that affect quality of life, making up a large part of the burden of disease, as well as the high cost.

In the CHART study, knowing about allergies or blood eosinophil counts did not add anything to improving prediction of symptom persistence. However, we do acknowledge that this information may aid in treatment decision choices for those individuals identified as being at high risk of having persistent asthma symptoms.

Of relevance to Australian readers is that CHART was validated in the Raine Study, a West Australian longitudinal birth cohort study where similar data were available at 3 years and subsequently asthma and respiratory outcomes at 5 years.

Often, many predictive tools only report on their performance in the population they are developed in, where they generally perform better since this is the dataset used to develop the prediction model. However, in order to be able to implement a prediction tool into clinical practice, it is vital that external validation be performed to show that the model is generalisable to other populations.

The fact that CHART’s performance in an Australian cohort was comparable would indicate that it is suitable for use in Australian children. Of note, although almost a quarter of the Canadian cohort were children of mixed ancestry, more than 60% were white, and if CHART were to be used in populations largely consisting of non-white ancestry, validation in the specific population of interest would be needed.

Given the symptom-based questions, CHART could potentially be implemented routinely within electronic medical records systems as a simple, non-invasive screening tool for children in a primary care setting. This could potentially be undertaken by a randomised trial by practice to see if early screening can prevent health care use in high risk children in Australia. The screening questions could be included in standard medical questionnaires, with an algorithm set to flag high risk patients for follow-up in 6 months or 1 year to repeat the screening, if necessary. The effectiveness of this could be assessed through a formal evaluation process.

If CHART were to be implemented into practice, it would also require national bodies such as Asthma Australia and the National Asthma Council to endorse its use in diagnostic guidelines. That requires real-world evidence in Australia.

Given sufficient evidence and a commitment to use this tool in primary care, this simple screening tool could potentially be a game changer in asthma management in young children. This is the first step in precision therapeutics for preschool children with wheezing disorders. Further work is necessary to identify which children would benefit from which types of therapy; that is, eosinophils may help identify children who should be treated with inhaled corticosteroids, and children with cough may need judicious use of antibiotics.

There is still some work to be done to identify targeted therapies in this age range.

Dr Rachel Foong is a Senior Research Fellow and biostatistician at the Wal-yan Respiratory Research Centre, Telethon Kids Institute and Curtin University.

Dr Graham Hall is the Chief Executive Officer of the Thoracic Society of Australia and New Zealand, and internationally recognized respiratory physiologist.

Dr Padmaja Subbarao is a clinician-scientist in Paediatric Respiratory Medicine, Co-lead of Precision Child Health, and Associate Chief of Clinical Research at The Hospital for Sick Children (SickKids) in Toronto.

The statements or opinions expressed in this article reflect the views of the authors and do not necessarily represent the official policy of the AMA, the MJA or InSight+ unless so stated.

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