Increased polymorphonuclear leukocytes (>75%). High discriminatory power when combined with history. 
mild leukocytosis (10,000 to 18,000/microliter)
Wall thickening, wall enhancement, and inflammatory changes in the surrounding tissues are additional findings seen in a CT scan of abdomen and pelvis. 
It has become common practice, especially in the US, for any patient presenting to the emergency department with abdominal pain suggestive of appendicitis, to have CT scan of the abdomen and pelvis, unless the patient is pregnant. A CT is also indicated in atypical presentations.
The sensitivity and specificity of CT scan in detecting acute appendicitis have been reported to be 94% and 95%, respectively. 
In pregnant women presenting with features of appendicitis, an abdominal sonogram should be performed to identify the appendix. If the sonogram examination is inconclusive, either an abdominal MRI (particularly in early pregnancy) or a CT scan should be performed. 
abnormal appendix (diameter >6 mm) identified or calcified appendicolith seen in association with periappendiceal inflammation
If positive, the possibility of ectopic pregnancy should be considered.
Indicated in atypical presentations. May be preferred in children in order to limit radiation exposure with CT scan. 
The sensitivity and specificity of ultrasound in detecting acute appendicitis have been reported to be 86% and 81%, respectively. 
aperistaltic or noncompressible structure with outer diameter >6 mm
If positive for red cells, white cells, or nitrates, an alternative diagnosis such as renal colic or UTI should be considered.
MRI can be used as an alternative to CT scan in pregnancy, particularly in early pregnancy. Its results are comparable to CT scan in pregnant patients for whom sonographic findings are equivocal for the diagnosis of acute appendicitis.  
abnormal appendix (diameter >6 mm) identified and evidence of periappendicial inflammatory changes
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