Aim of the study: to identify the signs of acute appendicitis delta signs - clinical, laboratory or ultrasound signs, whose change (delta) would allow to identify or deny the diagnosis of acute appendicitis without a computed tomography examination and thus to lower computed tomography rates.

This study consists of two parts:

• In the first part investigators enroll all patients (except pregnant) that are refered to Vilnius University Hospital Santaros clinics with suspected acute appendicitis in order to get cohort data. All patient get primary clinical evaluation, laboratory tests (WBC, CRP) an ultrasound examination.
• After primary evaluation if final diagnosis could not be made, and investigator still suspect acute appendicitis, participant is included in to randomised study part.
• Randomised sudy part has two arms: control and observation groups.
• Control group get the traditional diagnostic path - is refered to CT scan examination.
• Observation group get repeated evaluation after 8-12 hours and only than is diagnosis stays unclear, patient gets a CT scan.
• All patient are contacted after 30 days after visit to our hospital, to get information about their health status and possible additional visits to other hospitals or operations.

Inclusion Criteria:

• Patient with the symptoms of acute appendicitis: pain in the right lower quadrant, pain migration from epigastrium to right lower quadrant, nausea, rebound pain, elevated temperature.

Exclusion Criteria for randomized part:

• Pregnant patient.

Inclusion Criteria for randomized part:

• After primary clinical, laboratory and ultrasound examination diagnosis of acute appendicitis could not be confirmed or excluded.
• No other gynecological, urological ir gastroenterological pathology is confirmed.

Exclusion Criteria for randomized part:

• Clinical symptoms lasts for longer than 48 hours
• Signs of peritonitis

There are no future intensions make IPD available.