Computed tomography and ultrasound are increasingly recommended to establish the diagnosis of appendicitis.
However, population-based rates of misdiagnosis, or negative appendectomy, have not improved over time.
Dr David Flum and colleagues from Seattle determined the relationship between computed tomography and ultrasound and negative appendectomy.
The investigative team used data from the Group Health Cooperative on all patients undergoing appendectomy between 1980 and 1999.
The investigators conducted a longitudinal study to determine the frequency of negative appendectomy over time.
The team also conducted a case-control, medical record-based study of a subset of patients from the 1990s to determine the accuracy of computed tomography and ultrasound.
Of 4058 patients undergoing appendectomy, 50% were women with a mean age of 31 years, and 16% had an negative appendectomy.
| Computed tomography scans were 88% sensitive, with 97% positive predictive value
|Journal of the American College of Surgeons|
The overall incidence of negative appendectomy remained stable over time at 1.5 per 10,000 patient-years, as did the age and gender adjusted rate.
The team noted that in 1999, nearly 40% of patients had either computed tomography or ultrasound.
The aggregate sensitivity of these tests was only 74%, with a positive predictive value of 95%.
The investigators found that computed tomography scans were 88% sensitive, with 97% positive predictive value.
Ultrasounds were 70% sensitive, with a positive predictive value of 94%.
The investigators observed that more than 1 in 5 tests obtained in patients with negative appendectomy were positive for appendicitis.
Dr Flum's team concludes, “The rate of negative appendectomy was unchanged over time despite the introduction and use of computed tomography and ultrasound.”
“This appeared to be related to the inconsistent performance characteristics of the tests.”
“The results caution against over-reliance on computed tomography and ultrasound in diagnosing appendicitis.”
“This emphasizes the need for test benchmarking in routine practice before establishing protocols for presumed appendicitis.”