Introduction
The diagnosis of acute appendicitis in children remains challenging as symptoms can vary from mild abdominal pain to generalized peritonitis and septicemia. Historically, the diagnosis of appendicitis is mainly based upon clinical examination in combination with biochemical variables indicative for inflammation. A disadvantage of this diagnostic strategy was the relatively high negative appendectomy rate of 12.3–19%.
1, 2 To reduce this, an evidence-based guideline was proposed in 2010 by the Association of Surgeons of the Netherlands, which makes preoperative imaging mandatory in patients with suspected appendicitis.
3 Ultrasound is the preferred initial diagnostic imaging modality in both the adult and pediatric population.
3 Implementation of this guideline resulted in a significant decrease of negative appendectomies to 2.2%–5%.
2,4 Currently in the Netherlands, in 99.7% of the adult patients’ preoperative imaging studies are performed.
4
A consequence of the abovementioned policy is that the threshold to perform additional imaging studies is low in children presenting at the ER, especially since ultrasonography (US) can be performed quickly with minimal burden and harm for the patient. The downside of this lower threshold is the risk of potential inconclusive results from ultrasound, which may lead to exposure of children to harmful and expensive diagnostic procedures, such as CT scans, MRIs, or even diagnostic laparoscopies.
5‐7 Instead of these invasive diagnostic procedures, literature suggests that watchful waiting could be considered after non-visualization of the appendix on ultrasound.
8 Selection of patients with high probability of acute appendicitis would help to reduce exposure to abovementioned invasive diagnostic procedures. Clinical prediction rules (CPR), such as the Alvarado score,
9 were initially designed to diagnose appendicitis, but may also be used to rule out appendicitis. CPRs mostly consist of variables from medical history, physical examination, and biochemical testing. Large heterogeneity exists between CPRs in terms of included variables and cutoff values. Several studies showed that the value of these CPRs to diagnose appendicitis is low, reflected by positive likelihood ratios ranging from 1.7–8.5.
10‐15 Data regarding their value in ruling out appendicitis in the pediatric population are scarce.
10,16
The first objective of this study was to identify commonly applied CPRs through a literature search. The aim of the second part of the study was to investigate the value of the identified CPRs in ruling out appendicitis in the pediatric population in the Netherlands based on the negative likelihood ratios and thereby select CPRs that could potentially be used in a future prospective cohort study. Additionally, in order to determine if the use of imaging modalities could be reduced by adopting CPRs to rule out appendicitis, we determined the number of imaging procedures performed in patients that were qualified as low risk for the disease according to these CPRs.
Discussion
The aim of this study was to investigate the value of CPRs in ruling out appendicitis in our retrospective cohort in terms of negative likelihood ratio in order to select CPRs that could potentially be included in a future prospective cohort study.
In this study, seven CPRs had a negative likelihood ratio point estimate < 0.1, which therefore could impact clinical decision-making.
19 Therefore, these CPRs might be used in a future prospective cohort study comparing their ability to rule out appendicitis in children presenting with abdominal pain at the emergency department. Depending on the used CPR, in no more than 4% of the patients with a low suspicion of appendicitis, appendicitis was diagnosed within 30 days. In 30–46% of patients with a low suspicion of appendicitis, additional imaging studies had been undertaken.
Only a few studies have investigated the value of CPRs in ruling out appendicitis in children and they mostly expressed this value by sensitivity. The discriminatory power of a diagnostic test can best be displayed by likelihood ratios in our opinion, as it is not influenced by disease prevalence.
38
Recent systematic reviews, comprising 10–12 prospective derivation and validation studies with a total of around 4000 children, investigated the Alvarado score and PAS in the pediatric population and found negative likelihood ratios for these CPRs that were similar to our results; for the Alvarado score, negative likelihood ratios between 0.03 (95% CI, 0–0.36) and 0.38 (95% CI, 0.21–0.70) were found. Regarding the PAS, negative likelihood ratios ranging between 0 and 0.27 (95% CI, 0.20–0.43) have been reported.
10,16
Differences in negative likelihood ratios regarding the Alvarado score in the published negative likelihood ratios might be caused by different cutoff values that were used in the systematic reviews.
11,39 Furthermore, daily practice concerning the use of additional imaging might differ between countries.
39 Regarding the PAS, modest differences in negative likelihood ratio compared to the results in our study could be explained by the prospective nature of the included studies (versus our retrospective study) and by different inclusion criteria of the included population.
To our knowledge, we are the first to present negative likelihood ratios of other CPRs in addition to the Alvarado score and PAS in the same cohort. Furthermore, this study included multiple CPRs that do not incorporate extensive laboratory parameters. Multiple biochemical variables that are included in most CPRs, such as neutrophil count and leukocyte differentiation, are not routinely tested in the Netherlands when a child presents at the emergency department. Because of the identification and inclusion of both CPRs with and without extensive laboratory parameters, we were able to present a complete overview of all CPRs that can potentially be used in future prospective studies comparing their ability in ruling out appendicitis. In order to present a complete overview of all potential CPRs, we determined a low cutoff value of at least 50% of available data per CPR for inclusion in our analysis. We do realize that this cutoff value is low, but the aim of this study was to identify CPRs, investigate their potential in ruling out appendicitis, and investigate their appropriateness in the current diagnostic work-up as performed in the Netherlands in order to select them for a prospective cohort study. This cutoff value was determined prior to the identification of CPRs, and we realize that the use of a higher cutoff value might have led to a more stringent selection of only those CPRs that are most appropriate in our population.
The evidence-based guideline regarding the diagnosis and treatment of appendicitis, introduced by the Association of Surgeons of the Netherlands in 2010, emphasized reduction of the negative appendectomy rate. Imaging procedures are advocated to improve diagnostic accuracy and the consequence of this change has been the increased utilization of ultrasound as the initial imaging modality to evaluate abdominal pain in children in the Netherlands.
40 In 2010, preoperative imaging procedures were performed in 44% of patients presenting at the emergency room with abdominal pain in the Netherlands, compared to only 22% of the patients a decade earlier.
3,41 Currently in the Netherlands, in 99.7% of patients preoperative imaging is performed.
4 A recent study conducted in the USA found that 99.7% of pediatric patients underwent preoperative-imaging studies as well.
42 This differs significantly from the performance of preoperative imaging in the UK, where preoperative ultrasound and computed tomography (CT) were performed in 19.9 and 12.9% of patients respectively.
43 Ultrasound has a high frequency of inconclusive results, reported to range between 37 to 51% in the pediatric population.
7,44 Increased performance of ultrasound therefore results in increased use of costly and potentially harmful imaging studies, such as CT and MRI in pediatric patients.
In this study, in 30–46% of patients with a low suspicion of appendicitis according to these CPRs, additional imaging studies had been undertaken, whereas in no more than 4% of these patients (depending on the used CPR) acute appendicitis was diagnosed within 30 days. Nonetheless, because of the retrospective nature of this study, it might be possible that these additional imaging studies have not been solely performed to diagnose appendicitis, but also to exclude other potential diagnoses. Still, it raises the question whether or not watchful waiting should be considered for children with a low suspicion of appendicitis instead of additional imaging studies to rule out appendicitis. Opponents of this less aggressive diagnostic work-up mostly fear perforation of the appendix in case of complicated appendicitis.
45 However, several studies have not found clinical observation or re-evaluation to be associated with a significantly higher incidence of complicated appendicitis and perforation.
46,47 Time to presentation at the emergency department appears to be the main factor associated with perforation in children with appendicitis.
46,48 Furthermore, literature suggests that perforation can rarely be prevented, implicating that a correct diagnosis is more important than a rapid treatment strategy.
49
This study has several limitations. First, due to the single-center nature, generalizability might be reduced, although it was performed in a general teaching hospital. Second, the retrospective nature of this study might have led to selection bias and information bias. In case of wrong ICD code classification, patients might have been missed. We do realize that inclusion of 291 patients in 3 years’ time seems to be low for a large teaching hospital. This low number of patients could be explained by the fact that we only used ICD codes of acute appendicitis, acute abdomen, and general abdominal pain, because inclusion of children presenting with, for example, mainly symptoms of urinary tract infection would artificially decrease negative likelihood ratios and overestimate the value of the CPRs. Patient files with missing data were left out of the analysis. As a result, for only 34–90% of the patients the CPRs could be calculated. However, the aim of this study was not only to determine the ability of CPRs to rule out appendicitis in our cohort but also to investigate their appropriateness within the current diagnostic work-up as performed in the Netherlands. As mentioned previously, this study was performed in order to select appropriate and useful CPRs for a future prospective cohort study that can compare their value in ruling out appendicitis in our cohort. Nonetheless, missing data could have led to a selection bias, whereby the results of a CPR may have been inflated, leading to a low negative likelihood ratio. For example, in our population the CPR with the optimal negative likelihood ratio (Ohmann score) could only be calculated for 50.2% of the total population. Third, the small sample size causes wide confidence intervals for the calculated accuracy statistics.
In addition, CPRs are prone to subjective interpretation by the treating physician (e.g., variables of physical examination). In a prospective study by Mandeville, an interobserver agreement was found of 88 and 83.5% for the Alvarado score and the PAS, respectively.
48 Another problem is the potential partial verification bias. Patients were classified in the non-appendicitis group if there was no recurrence of abdominal pain during 30 days after initial presentation. Patients who went to another hospital during these 30 days could have been missed. On the other hand, there is no nearby facility that is comparable to the general teaching hospital where this study was conducted. Therefore, it can be expected that patients attend the same emergency department as during their initial presentation. Another issue is that a number of patients were included in the appendicitis group despite the fact that intraoperative or histopathological findings were not obtained, potentially also leading to misclassification. However, these patients were included in the APAC study, in which a radiologically confirmed simple appendicitis was an inclusion criterion.
In conclusion, we identified seven CPRs that could potentially be used in a future prospective cohort study to compare their ability to rule out appendicitis in the pediatric population in the Netherlands and other countries with comparable diagnostic work-up. Further prospective studies are needed to investigate if imaging studies could safely be omitted and be replaced by clinical monitoring or re-evaluation in children with a low CPR score.