Abdominal guarding
Abdominal guarding is the tensing of the abdominal wall muscles to guard inflamed organs within the abdomen from the pain of pressure upon them. The tensing is detected when the abdominal wall is pressed. Abdominal guarding is also known as défense musculaire.
Guarding is a characteristic finding in the physical examination for an abruptly painful abdomen (an acute abdomen) with inflammation of the inner abdominal (peritoneal) surface due, for example, to appendicitis or diverticulitis. The tensed muscles of the abdominal wall automatically go into spasm to keep the tender underlying tissues from being disturbed.

Diagnosis
Differential diagnosis
Abdominal aortic aneurysm
Appendicitis
Blunt force trauma to the abdomen
Bowel obstruction
Diverticulitis
Dyspepsia
Ectopic pregnancy
GERD
Ileus
Inflammatory bowel disease
Intussusception
Mesenteric ischemia
Nephrolithiasis
Ovarian cyst
Pancreatitis
Pelvic inflammatory disease
Perforated peptic ulcer disease
Pneumonia
Spontaneous bacterial peritonitis (SBP)
Urinary tract infection/pyelonephritis
Volvulus
Zoster
Skin lesions may not be visible until another day or two
Abdominal migraine
Abdominal wall strain/injury
Abscess (e.g. iliopsoas)
Hepatic or splenic contusion/laceration
Incarcerated hernia
Insect toxins (e.g. black widow spider)
Malingering
Pneumoperitoneum secondary to abdominal trauma
Septic miscarriage (See Miscarriage)

Laboratory findings
Complete blood count (CBC)
Blood urea nitrogen (BUN)/creatinine
Liver function tests (LFTs)
Glucose
Amylase/lipase
Urine culture
Urinalysis
Beta-human chorionic gonadotropin (beta-hCG)
Cervical cultures are recommended to diagnose pelvic inflammatory disease

Electrolyte and biomarker studies
Electrolytes

MRI and CT
CT diagnoses:
Organ contusion
Organ laceration
Aneurysm
Diverticulitis
Appendicitis

Echocardiography or ultrasound
Pelvic, abdominal and/or transvaginal ultrasound diagnoses:
Peritonitis
Ectopic pregnancy
Ovarian cysts
Fluid/blood secondary to trauma
Appendicitis
Aneurysm

Other imaging findings
KUB x-ray imaging (kidney, ureter, bladder) could reveal nephrolithiasis and bowel gas pattern

Other diagnostic studies
Symptomatic relief may be provided by paracentesis, which may also diagnose spontaneous bacterial peritonitis (SBP)
Gastrointestinal endoscopy may be used or patients with suspected peptic ulcer disease
Helicobacter pylori testing may also be used
Trial medications may be beneficial for the diagnosis and treatment of:
GERD/dyspepsia: Proton pump inhibitors or H2 blockers
Abdominal wall strain: Nonsteriodal anti-inflammatory drugs (NSAIDs)
Anxiety: Lorazepam
Zoster: Acyclovir

Treatment
Specific conditions need direct treatment
Hemodynamic status and life-threatening disease require immediate attention
Volume replacement with a possible blood transfusion, and with normal saline
For obstruction and persistent vomiting, place nasogastric (NG) tube

Pharmacotherapy
If perforated viscus or intra-abdominal infection suspected, administer broad-spectrum empiric antibiotics

Surgery and device-based therapy
Early sepsis, or evidence of hemorrhage may require surgery (likely to be life-threatening emergency)

References
Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3