Rationale: For clinicians it remains very difficult to predict whether preschool children with symptoms suggestive of asthma will develop asthma in later childhood.

Objective: To investigate whether measurement of fraction of exhaled nitric oxide (FE_NO), interrupter resistance (Rint) or specific immunoglobulin E (IgE) in 4-year-old children with suggestive symptoms can predict asthma symptoms up to age 8 years.

Methods: Children were recruited from the PIAMA birth cohort. All children with symptoms suggestive of asthma at age 3 or 4 years, who were invited for medical examination at age 4 (n=848), were eligible. Associations of FE_NO (n=308), Rint (n=482) and specific IgE (n=380) at 4 years with wheezing and asthma at the ages of 5–8 years were assessed using repeated measurement analyses. The added predictive value of these objective tests was then investigated by including parameters for clinical history in the model.

Results: FE_NO and specific IgE measured at 4 years were associated with wheezing and asthma at 8 years. Both tests also remained significant predictors after mutual adjustment and adjustment for clinical history: OR on wheezing at 8 years for FE_NO(¹⁰log-scale, per IQR) 1.6 (95% CI 1.1 to 2.2) and for specific IgE 2.8 (95% CI 1.9 to 4.1). Rint was significantly associated with wheezing at age 6, but not at 7 and 8 years.

Conclusions: In preschool children with symptoms suggestive of asthma, both FE_NO and specific IgE measured at age 4, but not Rint, improved the prediction of asthma symptoms until the age of 8 years, independent of clinical history.