Modified Alvarado score system results (MASS)
Among the MASS components, right lower quadrant tenderness was the most common, and nausea and/or vomiting was significantly related with acute appendicitis (p value 0.001).
shows that 49 patients had MASS scores
7 and 26 patients had MASS scores
7. Of these patients with a MASS score
7, five had a normal appendix according to pathology (negative appendectomy). Twenty-three patients with MASS scores
7 had true appendicitis according to pathology. Therefore, the sensitivity was 65.7%, specificity 37.5%, PPV 89.8%, NPV 11.5% and accuracy 62.7% for the Modified Alvarado Scale with a cutoff point of 7.
Modified Alvarado Scoring System with cutoff points of 6 and 7.
According to a cutoff point of 6, 63 patients had scores
6, and 12 patients had scores
6. Six patients had negative pathology for appendicitis (negative appendectomy) and ten with a score
6 had appendicitis according to the pathology report (false negative). Thus, the sensitivity of the MASS with a cutoff point of 6 was 85.1%, the specificity 25%, PPV 90.5% and NPV 16.7%, and the accuracy rate was 78.8% (Figure
ROC curve for diagnosis of acute appendicitis according to the Modified Alvarado Scoring System. The area under the curve is 0.837 with a standard error of 0.67 and confidence interval of 0.705 to 0.968.
Decision-making in patients suspected of having acute appendicitis is still a diagnostic challenge worldwide despite the advances in appendiceal surgery and the decrease in mortality because of appendicitis [22
]. According to some articles, negative appendectomy has been reported in 15% to 30% of appendectomies because of difficulties in making the diagnosis [4
]. This can impose a significance burden on the health system. For instance, 39,901 patients underwent negative appendectomies in the US in 1997, which resulted in an estimated total hospital charge of 741.5 million dollars [24
]. To assist and improve the diagnosis of acute appendicitis, a number of diagnostic modalities have been proposed, such as graded compression sonography and scoring systems [14
Ultrasonography is an affordable, noninvasive tool whose result can be obtained more quickly than for CT scans [19
]. Ultrasound has already been proved to have a high sensitivity and specificity in the diagnosis of acute appendicitis. Many data about are available, and 55% to 98% sensitivity and 78% to 100% specificity have been reported for ultrasonography [19
]. Variations in reported data may be due to differences in study design, sample size, physician experience or applied statistical techniques of various studies. Ultrasound is an operator-dependent technique, and the results vary depending on who is performing the ultrasonography.
In our study, ultrasound had 71.2% sensitivity, 83.3%specificity and 72.4% accuracy. Comparing this study with others reveals that ultrasound provides reliable findings for the diagnosis of acute appendicitis in Shariati Hospital, even though it is done by radiology residents without much experience. The PPV of ultrasonography was 97.4%, and the NPV was 25%. These results emphasize again that a positive ultrasonography for appendicitis is strongly in favor of a diagnosis of acute appendicitis. However, a negative ultrasound is not sufficient to rule out the diagnosis and discharge the patient.
Ultrasound was performed significantly more often in women: 39 (71%) males and 19 (95%) females. This may indicate that equivocal cases of appendicitis that require diagnostic aids and modalities are more frequent in females.
The Alvarado Scoring System is based on signs, symptoms and laboratory data. It is a very sensitive tool for classifying patients with suspected acute appendicitis [20
]. Taking into consideration that WBC differential counting is not easily and routinely done in many laboratories, the Modified Alvarado Scoring System (MASS), omitting the neutrophil count, has been used as an alternative. The MASS has been shown to be a quick and inexpensive diagnostic tool in patients suspected of suffering acute appendicitis. However, different accuracies have been reported for the MASS in different studies [14
]. We found that the most common MASS parameter was right lower quadrant tenderness (85.3%), and the only factor whose correlation with acute appendicitis was statistically significant was nausea and/or vomiting. This could be due to the small sample size of our study concerning the detection of other significant correlations.
In his original article, Alvarado suggested that patients with scores of 7 or higher should be operated on [20
]. In the same manner, for the MASS, the cutoff point of 7 has been commonly used [14
]. In our investigation, a sensitivity of 65.7%, specificity of 37.5%, PPV of 89.8%, NPV of 11.5% and accuracy of 62.7% were obtained for a cutoff point of 7. In 2008, Sun et al. suggested that a cutoff point of 6 provides a higher sensitivity and NPV in the Alvarado system, and may be more appropriate in comparison with the traditional cutoff point of 7 [25
Choosing the cutoff point of 6 in our study, the sensitivity of the MASS was 85.1%, specificity of 25%, PPV 90.5% and NPV 16.7%; the accuracy rate was 78.7%. Regarding these findings, it appears that a cutoff point of 6 for the MASS could be appropriate.
It would be more precise if we could include all patients suspected of having acute appendicitis and follow up those patients who did not undergo surgery, but patient follow-up has its own limitations, and an optimum follow-up was not possible for us. Moreover, we intended to have the pathology result of the resected appendix for the definite diagnosis. The estimated rate of negative appendectomy in our study was 10.7%, which is less than the accepted rate worldwide. We cannot make judgments about this rate until we have studied the perforation rate. In addition, a larger sample size is needed to estimate the precise negative appendectomy rate.