D2.145 - The utility of blood eosinophils, IgE and skin prick testing in paediatric asthma diagnosis

The new UK (NICE/BTS/SIGN) asthma diagnostic guidelines for children include the use of House Dust Mite skin prick test (SPT) or Total IgE along with eosinophil count (eos), where exhaled nitric oxide (FeNO), spirometry/reversibility (BDR) or peak flow (PEFv) testing is either unavailable, negative or the child is unable to complete the test. [SF1] A positive mite SPT (>3mm wheal diameter) or elevated Total IgE (>120KU/L) and eosinophil count (>0.5x10⁹cells/L) with symptoms suggestive of asthma are sufficient to make the diagnosis in children aged 5-16yrs.

Within an observational asthma diagnostic cohort study we investigated the sensitivity and specificity of these tests in children with suspected asthma.

Children aged 5-16yrs, referred from primary care with suspected asthma underwent clinical history, examination, FeNO, spirometry, BDR, PEFv, bronchial challenge, SPT, Total IgE, blood eosinophils, and completed 8 weeks inhaled corticosteroid treatment. A panel of at least 3 asthma specialists using all available data confirmed or rejected the diagnosis of asthma.

95 children underwent testing and had a definitive diagnostic outcome (51.6% male; mean (SD) age 10.0 (2.8) years; 73 Asthma, 22 Not Asthma). Positive house dust mite SPT had the lowest sensitivity and specificity of all the tests. Elevated Eos had the highest specificity which was not improved by the addition of Total IgE[SF1] . However, the standard lung function tests had higher specificity than the newly proposed tests, but not all children could complete these tests. Sensitivity of all the tests was poor. See Table below.

In children who are unable to complete standard lung function tests for asthma, an eosinophil count above 0.5x10⁹ cells/L may be an alternative test to consider; it has good specificity and is a better alternative to house dust mite SPT.