Blood test may help rule out acute appendicitis

A rapid blood test for the inflammatory marker S100A8/A9 shows potential as an aid in diagnosing acute appendicitis.

S100A8/A9 is a large protein that plays a pivotal role in the acute inflammatory cascade. Gastroenterologists measure S100A8/A9 in stool samples from patients with inflammatory bowel disease, using the level to quantify the extent of disease.

Diagnosis of acute appendicitis is one of the most difficult challenges for emergency physicians. Abdominal pain is the No. 1 presenting complaint in the emergency department, accounting for some 8 million patient visits annually. It’s no small challenge to separate the hundreds of thousands of patients with acute appendicitis from the millions with other reasons for their abdominal pain, observed at the annual meeting of the Society for Academic Emergency Medicine.

Presented was a pilot study exploring the assay’s potential for diagnosis of acute appendicitis.

The assay demonstrated greater sensitivity for acute appendicitis than did either abdominal CT or white blood cell count, the most widely utilized blood test for this purpose. The assay displayed mediocre specificity, but when used in conjunction with either a WBC count or abdominal CT, the assay had a 100% negative predictive value, said a pediatric and general surgeon at Children’s Hospital, Denver.

The multicenter observational study involved 181 patients ranging in age from 8 to 76 years who presented to emergency departments with lower-quadrant abdominal pain. Twenty-one percent were found to have acute appendicitis, while another two-thirds were categorized as having nonspecific or idiopathic abdominal pain.

A final determination of the diagnosis of appendicitis was made based on histologic study of appendectomy specimens on in the case of patients who didn’t undergo surgery by telephone follow-up 1-4 weeks after the emergency department evaluation.

Based on the encouraging performance of the assay, known as the AppyScore, in this preliminary study, larger, more definitive studies of the assay’s potential clinical role in the diagnosis of acute appendicitis are ongoing.

The assay’s high diagnostic sensitivity lends itself to a role as a screening blood test aimed at minimizing unnecessary radiographic and surgical procedures. A negative test would appear to be a solid indicator that a patient does not have acute appendicitis. A positive assay would need to be followed up with a high-specificity test, such as CT.

“The problem with the marker is its specificity is low. If the test is positive, you don’t know if you’re dealing with acute appendicitis or something else.” “Other things — particularly other GI pathology — will light up. Ovarian pathology does not. Pyelonephritis does about 50% of the time.”