Appendicitis Tests

Urgent safety information

If you have severe abdominal pain, especially if it moves to the lower right side, seek medical help immediately. Appendicitis can lead to a life-threatening infection if the appendix bursts.

Why this test may be ordered

• To evaluate abdominal pain that may be from appendicitis
• To find signs of infection or inflammation
• To rule out other conditions that mimic appendicitis (e.g., urinary tract infection, kidney stones, ectopic pregnancy)
• To confirm or rule out appendicitis with imaging

Preparation and collection

Blood and urine tests require no special preparation. For imaging tests, you may need to stop eating and drinking for several hours before the test. Your provider will give specific instructions.

Blood sample: a small needle is inserted into a vein in your arm to collect blood into a tube or vial, usually taking less than five minutes. Urine sample: you may be given a cleansing wipe and instructions for the 'clean catch' method to avoid skin germs. Imaging tests: you will be positioned on a table or bed; for CT scan, you may receive contrast dye as a drink, injection, or enema; for ultrasound, a gel is applied to your abdomen and a wand is moved over the area; for MRI, you lie still inside a tunnel-shaped machine.

Blood test: slight pain or bruising at the needle site. Urine test: minimal physical risk; contamination may lead to false results. CT scan: small amount of radiation exposure which slightly increases lifetime cancer risk; contrast dye may cause allergic reaction or slight burning. Ultrasound: no known physical risks, but accuracy depends on operator skill and patient body habitus. MRI: no radiation; but may be unsafe if you have certain metals or implanted medical devices; loud noises may require earplugs.

Understanding results

Your provider will review your symptoms, medical history, physical exam, and test results to determine if appendicitis is present. Imaging tests can confirm the diagnosis, while blood and urine tests provide supportive information. The following patterns are possible:

• High white blood cell count or high C-reactive protein (CRP) level: Infection or inflammation is present, but not specific to appendicitis. Limitation: Blood tests cannot diagnose appendicitis; a normal count does not rule it out. Next step: If appendicitis is suspected, imaging may be needed to confirm or rule out the diagnosis.
• Normal blood test results: No clear signs of infection or inflammation, but appendicitis is still possible. Limitation: Blood tests cannot rule out appendicitis. Next step: Further testing (e.g., imaging) may be necessary if symptoms persist.
• Imaging shows an appendix that is blocked, larger than normal, burst, or has an abscess: You likely have appendicitis. Limitation: Imaging is highly accurate but not perfect; very rarely, early appendicitis may not be visible. Next step: Surgery (appendectomy) is usually needed as soon as possible to prevent rupture.
• Imaging shows a normal appendix: Appendicitis is unlikely; other causes of your symptoms may be present. Limitation: Very early or mild appendicitis may sometimes be missed. Next step: Your provider will investigate other possible causes for your abdominal pain.

• Blood tests cannot diagnose appendicitis; they only indicate infection or inflammation. A normal white blood cell count does not rule out appendicitis.
• Urine tests cannot diagnose appendicitis; they help rule out urinary tract infections or kidney stones. Contamination may cause false results.
• CT scans use radiation which slightly increases lifetime cancer risk; children and unborn babies are more sensitive. Contrast dye may cause allergic reactions.
• Ultrasound is less accurate than CT for diagnosing appendicitis and depends on operator skill and patient body habitus.
• If you have certain metals or implanted medical devices, MRI may not be safe.

What to do next

Your provider will consider all test results together with your symptoms and physical exam. If appendicitis is confirmed, surgery (appendectomy) is usually needed as soon as possible to prevent the appendix from bursting. If your appendix has already burst, you must have surgery right away to remove the appendix and clean the infection from your abdomen.

• What is the nature and location of your abdominal pain?
• Do you have any other symptoms like nausea, vomiting, fever, or loss of appetite?
• Could you be pregnant?
• Do you have any allergies to contrast dye or iodine?
• Do you have any metal implants or devices in your body?

Evidence source

U.S. National Library of Medicine: Appendicitis Tests