Acute appendicitis is the most common surgical emergency in childhood. Despite access to current diagnostic modalities, diagnosis may be challenging since the child may have difficulty in articulating symptoms. Additionally there is a high frequency of atypical presentation and rapid progression. Delayed diagnosis in children is reported as being up to 60%. Delayed diagnosis >48hr increases the perforation rate from 21% to 71%. Around 20% of children presenting with appendicitis have perforated by the time they come to surgery.

Appendix perforation is associated with a prolonged hospital stay and increased cost. Once perforated, major complication rates increase from 1.2% to 6.4%, median bed stay increases from 2 to 6 days and hospitalisation costs are estimated at US $33,348.

Conversely, a false positive diagnosis leads to unnecessary surgery in 12%. It has been suggested that only 35% of surgical referrals with possible appendicitis actually need surgery thus impacting on resource use.

A reliable test, especially if painless, would be very useful. If positive the child could undergo early appendicectomy in expectation of a reduction in the perforation rate (and, therefore, reduction in hospital stay). If negative the child could be discharged home safely. No adequate biomarker has been identified.

Technology already exists to detect changes in Volatile Organic Compounds (VOC) in gases. VOC analysis is already used commercially to identify disease processes in animals and crops. Although VOC has been previously used to detect human diseases, it has never been used to look for changes in the composition of breath in appendicitis.

The investigators hypothesise that the composition of VOC's in children with appendicitis will differ from those without. The investigators anticipate these differences will be of diagnostic and prognostic value in clinical practice. The feasibility of collecting breath samples from children with possible appendicitis to allow VOC testing has not been examined.

Inclusion Criteria:

• Patients with suspected appendicitis
• Aged 5 and up to their 16th birthday on arrival to A&E
• Patients referred to the Paediatric surgical team that have presented to the Leeds General Infirmary through A&E, the Children's Assessment Unit, or via direct referral from another team or hospital.
• Consecutive presentations who can have some or all of VOC sampling during working week.

Exclusion Criteria:

• Patients with known alternative cause of abdominal pain (e.g. known Inflammatory Bowel Disease)
• Patients who are both admitted and discharged when no researcher is available