Untreated appendicitis can be life-threatening
Scientists are hopeful of developing a simple urine test which will be able to detect appendicitis.
The condition may be life-threatening without emergency surgery, but can be difficult to diagnose, especially in younger people.
Now a team at the Children's Hospital Boston has pinpointed a protein in the urine which might be a tell tale sign of the condition.
The research features online in Annals of Emergency Medicine.
An easier way to detect appendicitis would represent a major breakthrough, reducing the risk of serious complications if it is missed, or of unnecessary surgery if it is wrongly diagnosed.
Despite improvements in imaging technology, recent figures suggest as many as 30% of children who undergo appendix removal do so unnecessarily, while up to 45% diagnosed with appendicitis already have a ruptured appendix.
The Boston team used a technique called mass spectrometry to analyse 12 urine samples from children.
They identified 57 compounds associated with immune response and inflammation which might potentially be a sign of appendicitis.
Inflammation of a small pouch connected to the colon
Can be caused by infection or obstruction - but in many cases the cause is unclear
Regarded as a medical emergency because a ruptured appendix can lead to potentially serious or even fatal complications, such as blood poisoning
Further tests carried out on 67 children seen at the hospital for suspected appendicitis narrowed the field to seven promising candidates.
The best of them was a protein called leucine-rich alpha-2-glycoprotein (LRG).
The researchers found that LRG levels were significantly elevated in diseased appendices - even those that appeared normal on scans.
They also found that the more severe the disease, the higher the level of LRG was.
The researchers accept that mass spectrometry is not widely available in hospitals, but they believe it might be possible to develop a rapid urine dipstick test for the protein.
Researcher Dr Richard Bachur said: "Recent diagnostic advances have focused on advanced radiologic procedures, such as computed tomography and ultrasound, but these resources are not universally available and can delay diagnosis.
"Although these advances have improved the diagnosis and decreased complications from appendicitis, CT scans also expose children to radiation that may increase the lifetime risk of cancer."
However, the researchers accept that their findings may only be relevant to children, and that patterns of tell tale biomarkers may vary in older patients.
They stress that more research on adults is needed.
Mr Geoffrey Glazer, a consultant general surgeon based at London's Wellington Hospital, agreed that diagnosing appendicitis could pose problems.
"The problem for surgeons is that they would rather take out a lilywhite appendix than leave a bad one in," he said.
However, he said appendicitis often mimicked other inflammatory conditions, such as diverticulitis.
He said more work was required to determine not only whether LRG was a relevant marker for adults as well as children, but also whether it was specific to appendicitis, and not other related conditions.
Dr Anton Emmanuel, medical director of the digestive disorders charity Core, said the test, if proven to be useful in all populations, could potentially be very useful.
"The fact that this is a non-invasive test is also a big bonus. In time, it is likely to be one of a number of tests that will prove diagnostically useful in establishing whether or not there is appendicitis.
"The question is whether surgeons and patients will trust a negative result over a clinical impression."