Typical history and physical examination are usually sufficient to reach the diagnosis of acute appendicitis.  It has, however, 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.
Atypical presentations that do not have the classical symptoms of central abdominal pain that shifts to the right iliac fossa or associated features of anorexia and vomiting should also have either an ultrasound or a CT scan. Women of childbearing age should have a pelvic examination to rule out other pelvic pathology. Pregnant women presenting with right-sided abdominal pain, with nausea and vomiting, pose an even greater challenge and should proceed to ultrasound examination, followed by MRI or CT scan if needed. 
Abdominal pain is the main presenting complaint. Pain typically starts at the mid-abdominal region and later (1 to 12 hours) shifts to the right lower quadrant. Pain is usually constant in nature and with intermittent abdominal cramps and is usually worse on movement and coughing.
Location of the pain may vary depending upon the position of the appendix:
Retrocaecal appendix may cause flank or back pain
Retroileal appendix may cause testicular pain due to irritation of the spermatic artery or ureter
Pelvic appendix may cause suprapubic pain
A long appendix with tip inflammation in the left lower quadrant may cause pain to that region.
Anorexia is another important symptom almost always associated with acute appendicitis.  Without anorexia the diagnosis of acute appendicitis is in question. Nausea and vomiting are also present in 75% of patients.  Vomiting usually occurs only once or twice. Absolute constipation is a late feature.
The sequence of presentation in 95% of the patients with acute appendicitis usually starts with anorexia, followed by abdominal pain and then vomiting (seen only in 75% of patients).  However, in pregnant patients, the only features shown to be significantly associated with a diagnosis of appendicitis are nausea, vomiting, and local peritonitis. 
Usually, there are no significant changes in vital signs. Body temperature may be slightly increased (by an average of 1°C; 1.8°F). In patients presenting with a high-grade fever, another diagnosis should be considered.  Tachycardia and fetor may also be present. 
A classic sign is right lower quadrant abdominal tenderness (McBurney's sign) and localised rebound tenderness, if appendix is anterior. There may also be pain in the right lower quadrant after compressing the left lower quadrant (Rovsing's sign).
Pain may be elicited with the patient lying on their left side and slowly extending the right thigh to cause a stretch in the iliopsoas muscle (psoas sign) or by internal rotation of the flexed right thigh (obturator sign).
Bowel sounds may be reduced, particularly on the right side compared with on the left.
Classical abdominal findings may not be present if the appendix is in an atypical position.
Patients with perforation may present acutely unwell with hypotension, tachycardia, and a tense, distended abdomen with generalised guarding and absent bowel sounds.
A palpable mass may be felt if the appendiceal perforation has been contained by the omentum, resulting in a peri-appendiceal abscess.
All patients with abdominal discomfort should have an FBC taken. Mild leukocytosis (10 to 18 x 10^9/L or 10,000 to 18,000/microlitre) with increased neutrophils is usually present.
If clinical findings suggest acute appendicitis, further investigations should not delay proceeding to surgical management.  In the US, most nonpregnant patients presenting to the emergency department with abdominal pain suggestive of appendicitis will have a CT scan of the abdomen and pelvis. This practice may vary in other countries and depend on availability of CT scan.
Patients with a palpable abdominal mass should also have either an ultrasound or an abdominal CT. 
Although CT scan has greater sensitivity and specificity than ultrasound in diagnosing appendicitis,   the latter has the advantage of being readily available, rapid, and able to be performed at the bedside.  In children, ultrasound may be preferred over CT scan in order to limit radiation exposure.  If, on ultrasound, a normal appendix is visualised in its full length, then acute appendicitis can be excluded. However, this is rarely the case, and the greatest utility for ultrasound is to detect alternative causes of abdominal pain. 
Appendiceal CT scan is increasingly used as the initial diagnostic test for acute appendicitis, and it is routine practice in the US to request a CT for patients presenting to the ED with features of acute appendicitis.  There is some opinion that CT scan should be used selectively for patients with atypical presentations, as delay in surgery increases the rate of appendiceal perforation.  Scanning protocols may vary between regions and physicians should consult local hospital guidelines. Intravenous contrast-enhanced CT scan with or without oral contrast has 100% sensitivity compared with 92% sensitivity in non-intravenous contrast-enhanced CT scan.  
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. 
A urinalysis should be performed to exclude possible urinary tract infection or renal colic. Sexually active women of childbearing age should have a urinary pregnancy test.
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