Background and Aim Recurrent respiratory tract infection (RTI) is a frequent presenting complaint in the general paediatric clinic. Children are often tested to screen for possible underlying immunodeficiency and Cystic Fibrosis. We aim to evaluate the indications for performing functional antibody assay (FAA) and how the results affected our clinical management.

Methods We retrospectively studied children who had FAA (Haemophilus, Pneumococcus, and Tetanus) sent over a 1-year period in our district general hospital. Clinical records were examined for patient’s characteristics and FAA results.

Results Between September 2010 and September 2011, 48 patients had FAA performed. Ages ranged between 1 and 18, with 6% under 13 months old, and 85% under 8 years old. In 77%, FAA was performed because of recurrent RTI; 10% because of other recurrent infections; and in 13% no indication was documented. 35% of patients had low Haemophilus IgG, 79% of patients had low Pneumococcal IgG, and 1% of patients had low Tetanus IgG.

37/48 patients had low FAA; 29 of these patients were recommended to receive booster vaccines. 9/15 of parents reported reduction of RTI post booster vaccine. 10/12 of patients had their FAA documented to have returned to normal.

Conclusions 60% of patients with low FAA had reduced RTI post booster vaccine. FAA should not be done in children less than 13 months of age as the booster dose is due at 12–13 months and a low level may not necessarily change management. FAA is a useful tool for investigating children with recurrent RTI.