Comparison of ultrasound and the Alvarado score for the diagnosis of acute appendicitis

Abstract

Background: The Alvarado score assigns a numerical value to eight signs and symptoms associated with acute appendicitis. Practically speaking, the Alvarado score is equivalent to one's degree of clinical suspicion. Ultrasound is used in many institutions to aid in the diagnosis of acute appendicitis. The following study compares the accuracy of the two modalities and examines the value of using both modalities together.

Study design: This study is a retrospective review of all patients who underwent appendectomy for presumed acute appendicitis at our institution in 1995. Seventy-five patients had a preoperative ultrasound and all 94 patients received an Alvarado score from a retrospective chart review.

Results: Ten (10.6%) patients had a normal appendix removed. Ultrasound alone resulted in a correct diagnosis 87% of the time. Using the Alvarado score alone, a correct diagnosis was made 88% of the time. If the ultrasound alone were used for diagnosis, seven acute appendices would have been missed (10% false negatives) and three unnecessary operations would have been performed (4.6% false positives). If the Alvarado score alone were used for diagnosis, four acute appendices would have been missed (5.9% false negatives) and five unnecessary operations would have been performed (7.2% false positives). There were 45 true positives and no false positive results when both modalities were positive for appendicitis. When the Alvarado score was negative or equivocal, the addition of ultrasound decreased the false negative rate by 75%.

Conclusion: When comparing ultrasound to the Alvarado score for the diagnosis of acute appendicitis, neither one is significantly advantageous. However, the false positive rate is reduced to zero when both studies are positive and ultrasound improved diagnostic accuracy when the Alvarado score was negative or equivocal. There is no advantage of ultrasound over the Alvarado score for the diagnosis of acute appendicitis. Ultrasound is unnecessary when one's degree of clinical suspicion is high. However, the additional information provided by ultrasound does improve diagnostic accuracy in the case of a negative or equivocal Alvarado score. Acute appendicitis is the most common surgical abdominal emergency with a lifetime prevalence of approximately one in seven.