Negative Appendectomy Rate in Urban Referral Hospitals in Tanzania: A Cross-sectional Analysis of Associated Factors

Masawa Klint Nyamuryekung’E, Ali Athar, Miten Ramesh Patel, Aidan Njau, Omar Sherman, Ahmed JusabanI, Ali Akbar Zehri
The Section of General Surgery, Department of Surgery, The Aga Khan Hospital, Dar es Salaam, Tanzania

Correspondence to: Dr Ali Akbar Zehri; email:,

Received: 21 April 2020; Revised: 29 June 2020; Accepted: 6 July 2020; Available online: 20 July 2020


Background: Acute appendicitis (AA) has a lifetime risk of 8.3% with a consequent 23% lifetime risk of emergency appendectomy. In atypical presentation, making a clinical diagnosis is difficult, leading to a high perforation rate (PR) or misdiagnoses and high negative appendectomy rates (NAR). This study aimed to establish NAR and explore the associated factors and possible attainable solutions to reduce it in urban referral hospitals in Tanzania. Methods: This was a cross-sectional study with 91 consecutive patients, aged 10 years and older undergoing appendectomy for suspected AA with histological evaluation of specimens. The study was powered to detect the NAR at 95% confidence level and 80% power. Results: The histological NAR was 38.5% and the perforation rate was 25.3%. The Alvarado score (AS) was rarely applied (6%), despite a demonstrated ability in this study to decrease the NAR by half. Females were four times more likely to undergo negative appendectomy than males. Conclusion: The NAR is clinically significant as about two out of every five patients undergoing emergency appendectomy for suspected AA do not require the procedure. The AS is underutilized despite a demonstrated ability to decrease the NAR. We recommend that the AS be incorporated in the management of patients with suspected appendicitis. 

Keywords: Negative appendectomy rate, Sub-Saharan Africa, Alvarado score, Appendectomy, Suspected acute appendicitis

Ann Afr Surg. 2021; 18(2): 109–114
Conflicts of Interest: None
Funding: None
© 2021 Author. This work is licensed under the Creative Commons Attribution 4.0 International License. 


Acute appendicitis (AA) has a lifetime prevalence of between 6.7% and 8.6%, with a corresponding lifetime risk for emergency appendectomy of 12.0% to 23.1% (1). Despite the frequent occurrence, making a correct clinical diagnosis is often difficult in an atypical presentation. Delay in diagnosis leads to perforation while misdiagnosis results in unnecessary appendectomy (2, 3).
Low negative appendectomy rate (NAR) has been traditionally interpreted as being associated with missed early AA and, consequently, progression to perforation. By contrast, a high NAR while reducing the risk of missed early AA commonly results in subjecting patients to unnecessary surgery (4). While the relationship described above is still prevalent in resource-limited health services, imaging technologies available in highly resourced health services can reduce the NAR without increasing the perforation rate (5,6). A high NAR leads to unnecessary surgical intervention with its associated risk of morbidities, economic burden, and with the potential adverse consequences of unnecessary anesthesia (7–11).
The precision of diagnosis of AA is a major determinant of NAR. This precision can be increased by the use of medical imaging, clinical scoring systems, and laparoscopy. Diagnostic scoring systems such as the Alvarado score (AS) have parameters with a positive correlation to the diagnosis of AA (12). Using the AS, the most established scoring system, a score of less than 5 has been endorsed as having enough sensitivity to virtually rule out AA (13). Medical imaging displays the appendix and associated features of inflammation during AA. Diagnostic performance of ultrasound for suspected AA yields an overall NAR of about 4.9% to 9.7%(14). Use of computer tomography (CT) results in a NAR of 2.5% to 8.5% (15).
In Sub-Saharan Africa, AA is associated with significant potentially avoidable morbidities and mortalities. This is due to prehospital delays and in-hospital delays caused predominantly by limited human resources, infrastructure, and diagnostic capacity (16). Access to laparoscopy and magnetic resonance imaging is limited in this setting. This situation is hypothesized to adversely impact the NAR, which ranges from 17% to 33.1% (17,18).
This study was undertaken to establish the baseline NAR, and explore associated factors and possible attainable solutions to reduce it in urban referral hospitals in Tanzania. Furthermore, these parameters could serve as measures of performance and as evaluation parameters for future interventions aimed at improving AA case management in this region.


Materials and Methods

This was a cross-sectional analytical study conducted in four urban referral hospitals in Dar es Salaam City, Tanzania, from May 2018 to April 2019. Three hospitals were public district referral hospitals with fully equipped laboratories and radiology services offering ultrasound services; however, CT was not available. The fourth hospital was a private referral hospital with CT services in addition to the diagnostic capacity of the public hospitals. Patients who underwent appendectomy or emergency laparotomy for suspected AA above the age of 10 years were included. Pregnant women, those who intraoperatively had alternative diagnoses, and those who underwent incidental appendectomy were excluded.
We applied a finite population correction of 120. This reflected the total number of appendectomy procedures that would be done during the study period with the outcome of interest. Based on 95% confidence level and power of 80%, using the 33% NAR and a 5% precision level, the minimum sample size required was 89 (18). Given the attrition rate and lost data a sample size of 95 was targeted.
Appendectomy specimens were collected with corresponding data abstraction tools. The surgical specimens were analyzed histologically by a consultant anatomical pathologist. All appendix specimens collected underwent histological analysis. Standard quality assurance processes of the pathology laboratory mandated random 10% confirmation by a second consultant pathologist.
We collected information on patient demographics, lag time—defined as duration of onset of illness in days until appendectomy—, signs, symptoms of the patient during illness along with the white blood cell count and differentials. AS use, the score assigned, as well as medical imaging use and operative findings were acquired. The main outcomes were appendix histological diagnosis.
AA was defined histologically as transmural attendance of acute inflammatory cells, and negative appendectomy was defined as a lack of transmural attendance of inflammatory cells. The NAR was determined as a ratio of histologically negative appendicitis to the total number of appendectomy specimens. 
Descriptive statistics such as proportions, means, median, range, and standard deviations were calculated. Continuous variables were tested for normality using the Shapiro–Wilk test and proportions were compared by chi-square (χ2) and Fisher’s exact tests.
We calculated AS for all patients from the collected data. Each parameter used to make a radiological diagnosis of AA for a CT abdomen was given a score of 1 when present. The parameters for CT were appendix diameter >7, free fluid in the right iliac fossae (RIF), fat stranding, and the presence of appendicolith. As the scores increased, the likelihood of AA increased. In a similar manner, ultrasound features for diagnosing AA used to create the ultrasound score were RIF fluid, diameter of appendix