Tests

Investigations in a patient with RIF pain:

• Urinalysis – note that up to 30% of patients with appendicitis will have an abnormal urinalysis (often mildly positive for RBC, WBC or protein); send urine for urgent gram stain if in doubt [6]
• Urinary beta-hCG – to exclude ectopic pregnancy in any female of child-bearing age
• Full blood count – 80-90% of patients with appendicitis will have a raised white cell count (WCC) (>10 x 105). While helpful, WCCs will also be raised in other causes of RIF pain and cannot rule in or out the diagnosis [2,7]
• C-reactive protein (CRP) – shows specificity and sensitivities of around 50-60%. Again, CRP is helpful but fairly non-specific, and is more useful if interpreted in combination with the WCC [2]The combination of a normal CRP and WCC has a negative predictive value for appendicitis in the region of 80-90% [8]. Therefore normal inflammatory markers make appendicitis less likely but cannot rule it out.
• Plain abdominal x-ray – there is no role for plain films in patients with RIF pain, unless to look for another diagnosis, such as obstruction

Learning bite

90% of patients with appendicitis will have a raised WCC/CRP.