The aim of the study is to evaluate whether patients with early equivocal appendicitis can be observed instead of immediate diagnostic imaging. Half of the patients are randomly assigned to observation group, while the other half will undergo diagnostic imaging. The hypothesis is that resolving appendicitis is common in these patients. Thus, in observation group there will be fewer patients with appendicitis diagnosis and observation reduces the use of diagnostic imaging and surgery.

For the study equivocal appendicitis is defined as clinical suspicion of appendicitis with Adult Appendicitis Score between 11 and 15. The estimated prevalence of appendicitis in such patients is around 50%.

Diagnostic imaging is done using conditional computed tomography i.e. abdominal ultrasound first and computed tomography only after negative or inconclusive appendicitis after ultrasound.

In observation group repeated clinical examination is done after 6-8 hours interval with repeated blood test for calculation of Adult Appendicitis Score. Patients with decreasing score value continue observation without imaging, whereas patients with the same score value or higher (but below 16) undergo diagnostic imaging as in other group. Laparoscopy is done without imaging in patients with high score (16 or higher). Antibiotics are not allowed, but prophylactic antibiotics during induction of anesthesia are allowed.

Inclusion Criteria:

• Clinical suspicion of acute appendicitis
• Equivocal appendicitis defined by Adult Appendicitis Score: Score ≥11 and ≤15.

Exclusion Criteria:

• C-reactive protein >99 mg/l
• Time from symptom onset over 24 hours
• Pregnancy
• Antibiotics given within last 24 hours
• Suspicion of other disease than appendicitis, that would require immediate interventions such as surgery, diagnostic imaging or gynecologic consultation
• Missing written informed consent
• Patient randomized earlier to the study