Acute Abdominal Pain Investigations:  Patients should have a full blood count, urea and electrolytes, glucose and amylase taken to look for evidence of dehydration, leucocytosis and pancreatitis. Urinalysis is useful in suspected renal colic and pyelonephritis. An erect chest X-ray may show air under the diaphragm, suggestive of perforation, and a plain abdominal film may show evidence of obstruction or ileus. An abdominal ultrasound may help if gall stones or renal stones are suspected. Ultrasonography is also useful in the detection of free fluid and any possible intra-abdominal abscess. Contrast studies, by either mouth or anus, are useful in the further evaluation of intestinal obstruction and essential in the differentiation of pseudo-obstruction from mechanical large-bowel obstruction. Other investigations commonly used include CT (seeking evidence of pancreatitis, retroperitoneal collections or masses, including an aortic aneurysm or renal calculi) and angiography (mesenteric ischaemia). Diagnostic laparotomy should be considered, when the diagnosis has not been revealed by other investigations. All patients must be carefully and regularly re-assessed (every 2-4 hours) so that any change in condition that might alter both the suspected diagnosis and clinical decision can be observed and acted on early.  Key Concept: Sometimes, renal stones are not evident in ultrasonography, if these are small in size. Then, CT-KUB should be considered. Ref: Davidson Ed 23 Pg 787