This study showed negative appendectomy rate in patients diagnosed with acute appendicitis from 2015 to 2019, which was 8.6% (n = 77). When compared with other studies, the rate of negative appendectomy was 3-15%, which depended on the medical facilities and surgeons’ experience in each center. However, the negative appendectomy rate in our center was similar to the previous studies [15]. Furthermore, this study showed the relationships between several factors and negative appendectomy rate. The study found that female, age £ 40 years old and history of diarrhea were related to increase in the negative appendectomy rate. Whereas leukocytosis with cells shift to the left (WBC 10,000 and N 75%) and positive appendicitis from abdominal ultrasonography and CT scan were found to decrease negative appendectomy rate.
From this study, we found that female (70%) was more common in negative appendectomy group increasing negative appendectomy rate for 2.23 times when compared with male. Studies in the United States and Saudi Arabia also supported that the majority of negative appendectomy was found in female (65% and 64.3%, respectively). That could be explained by female patients having more chances of negative appendectomy due to gynecological problems mimicking acute appendicitis [9,15-17].
Age was also a factor related to negative appendectomy. This study found that age less than forty significantly increased the rate of negative appendectomy 2.35 times when compared to age more than 40 years old (P=0.003). According to the Courtney’s study [7], they found that more preoperative CT scan use in patients older than 45 years old did not significantly reduce the negative appendectomy rate. They assumed that it might have been a consequence of the initially low rates of negative appendectomy in this age group. Elderly patients needed to undergo further investigations, especially abdominal ultrasonography or CT scan, than younger patients before receiving surgery because they had several differential diagnoses of abdominal pain when compared with younger age patients. So, the negative appendectomy rate in younger patients was higher than older patients as in our results.
History of diarrhea and abdominal pain might confuse the diagnosis eventually leading to negative appendectomy. These symptoms might mimic enterocolitis or irritable bowel syndrome (IBS). According to Lu’s study, Rome-II-defined IBS increased the rate of negative appendectomy (OR=2.65, 95%CI 1.34-5.23) [18]. This reason might be explained by hyperperistalsis of the bowel movement and other patients’ abdominal pain complaints that might cause the clinicians’ misdiagnosis between acute appendicitis and other diseases of abdominal pain. These reasons might affect the patients undergoing appendectomy and occurrence of the negative appendectomy rate. Besides, the clinical features of acute appendicitis were less likely to have diarrhea. Therefore, if the patients have abdominal pain with diarrhea, the clinicians should be concerned when diagnosing acute appendicitis [18].
Complete blood count was the important tool to help the differential diagnosis in patients with suspected acute appendicitis. The leukocytosis was defined as WBC 10,000 and cells shift to the left was defined as neutrophil 75% [5]. These were two of the factors decreasing negative appendectomy. According to Muhammed Saaiq et al, using WBC cutoff level of 10000/µL yielded the sensitivity of 92%. The negative appendectomy rates were decreased from 43.5% to 8.18% [19].Another point from this study stated that the sensitivity, specificity, positive predictive value and negative predictive value of elevated leukocyte counts were 91.81%, 43.55%, 81.77% and 65.85%, respectively [19].
Both abdominal ultrasonography and CT scan showed positive acute appendicitis that decreased the negative appendectomy rate in this study. Several large database studies, meta-analyses and single institution studies credited abdominal CT scan with reducing the negative appendectomy and in the landmark study of Rao et al, the CT rates in the United States had risen rapidly[20] and negative appendectomy rate of 1–3% had been reported [21-22]. This study demonstrates that abdominal CT scan is the standard for diagnosing patients with suspected acute appendicitis. Moreover, many previous studies showed that imaging studies significantly impacted the decreasing incidence of negative appendectomy. According to Mariadason et al, CT scan use was beneficial in lowering the negative appendectomy rate from 9.2% to 3% [8]. However, our study had just 46% and 37% of patients who underwent abdominal ultrasound and abdominal CT scan, respectively. In developing countries including Thailand, the usage of further investigations especially CT scan of abdomen to diagnose acute appendicitis should be requested carefully due to the cost and availability of facilities in each center. Moreover, the negative appendectomy rate was quite low (11.1%) in patients who did not undergo any imaging studies in our study.
This study was a five-year retrospective single center study. The data was collected in a high-volume medical university center. The limitation of this study was the incomplete history taking of comorbidity or other illness which could be analyzed more precisely, and the incomplete data of imaging details compared with final pathologic results which could imply sensitivity and specificity. A prospective study collecting patient and investigation data in more details might be helpful to clarify the risk, predictive factor of negative appendectomy and might show the accuracy and precision of our institutes’ facilities.