Plain abdominal radiographs:
Colonic Dilation ≥6 cm diameter
Loss of haustra, "thumb-printing" (bowel edema)
Air-fluid levels
Abdominal Ultrasound:
Thin colonic walls with loss of haustra coli
Diameter ≥6cm with gaseous content
Labs:
Leukocytosis
Electrolyte derangements: Hypokalemia, Hypomagnesemia
Elevated ESR/CRP
Anemia
Hypoalbuminemia
Colonic Dilation ≥6 cm diameter
Loss of haustra, "thumb-printing" (bowel edema)
Air-fluid levels
Thin colonic walls with loss of haustra coli
Diameter ≥6cm with gaseous content
Leukocytosis
Electrolyte derangements: Hypokalemia, Hypomagnesemia
Elevated ESR/CRP
Anemia
Hypoalbuminemia
Toxic megacolon
Small bowel obstruction
Mesenteric ischemia
Large bowel obstruction
Neutropenic enterocolitis 
Volvulus, Neoplastic Disease, Paralytic ileus, Pseudo-obstruction
Short bowel syndrome
Colitis