CAN THE ADDITION OF A URINE TEST STRIP FACILITATE THE DIAGNOSIS OF AN ACUTE APPENDICITIS? A DIAGNOSTIC ACCURACY STUDY

Introduction

Suspected acute appendicitis is one of the most common indications for emergency surgery in abdominal surgery

(1). Given that the procedure itself is technically relatively simple and considering the fact that neglected appendicitis is accompanied by a high morbidity rate, surgeons have a low threshold for operation if there is any suspicion of appendicitis, which results in a relatively high rate of acceptable negative appendectomies (up to about 15%) (2). Imaging methods in terms of ultrasound or MSCT can be of significant use in the diagnosis of acute appendicitis, but with certain limitations. In the adult population, unlike children, ultrasound has very limited value. On the other hand, MSCT has a high sensitivity in the diagnosis of acute appendicitis, but due to the unavailability and cost of the examination, as well as the significant harmful radiation, this examination could not be established as a routine examination in cases of suspected acute appendicitis

(3). For all of the above, decision-making in cases of suspected acute appendicitis still relies predominantly on the surgeon’s clinical assessment, which is based on data from the physical examination, medical history, and laboratory tests (4). Given the rather wide differential diagnosis of abdominal pain, numerous scoring systems have been proposed with the aim of facilitating the correct decision-making in the diagnosis of acute appendicitis. Unfortunately, none of them has proven to be ideal (5,6).

One of the most popular is certainly an Alvarado scoring system (7), designed in 1986, that combines certain clinical and laboratory parameters (Table 1). In our previously published case-control retrospective pilot study, we concluded that acute appendicitis in emergency settings may be successfully ruled in with high accuracy based on elevated WBCs and negative urine test strip in combination with presented clinical symptoms (8). We also observed that CRP did not contribute to the overall diagnostic accuracy, in contrast to previously published studies. Based on our preliminary findings we have prepared a prospective diagnostic accuracy study protocol with two distinct objectives:

(1) To evaluate the diagnostic accuracy of the Alvarado score within our patient population and determine its usefulness as a decision-support tool for surgeons when considering operative management. The results of this objective were published in Acta Chirurgica Belgica Journal in 2024 (9).

(2) To validate and assess the diagnostic accuracy of a newly proposed scoring system incorporating urinalysis in addition to other clinical and laboratory parameters (Table 2).
This study was built upon a previously published case-control pilot study, aiming to validate its preliminary findings.

* For each of the present symptoms, signs or laboratory findings, an adequate number of points is assigned.
A score of 5 or 6 is compatible with the diagnosis of acute appendicitis.
A score of 7 or 8 indicates a probable appendicitis.
A score of 9 and 10 indicates a very probable appendicitis.

Materials and Methods

Subjects

From June 2018 to May 2020, a total of 176 adult patients with suspected acute appendicitis were prospectively enrolled in a diagnostic accuracy study.
During the study period, all patients presenting to the Emergency Surgical Department of University Hospital Sveti Duh with right lower quadrant abdominal pain—and without a history of appendectomy—were evaluated by a single surgeon (author Branko Bakula, BB). Those deemed to have suspected appendicitis were included. The study received approval from the Hospital Ethics Committee, and written informed consent was obtained from all participants. The current paper addresses the second objective of the prospective study.

Methods

All patients underwent standard diagnostic evaluation, including a physical examination and collection of all variables required for the calculation of the Alvarado score (total white blood cell count (WBC), percentage of neutrophils). Additionally, the C-reactive protein concentrations (CRP) (immunoturbidimetry method on Beckman Coulter AU680 analyzer (Beckman Coulter, Brea, California, US) and urine test strip results (iChem Velocity Urine Chemistry Strips for in vitro use with the automated iChemVELOCITY System (Beckman Coulter, Brea, California, USA)) were also recorded. Positive findings of blood (≥0.3 mg/L) and/or leukocytes (≥25 WBC/µL) on the test strip were considered as a „positive“ result.

However, neither the Alvarado score nor the newly proposed scoring system incorporating urinalysis were not calculated during the initial assessment as surgical decision-making was based exclusively on clinical judgment and entirely independent of any scoring systems.

Urinalysis, traditionally used to exclude urinary tract pathology, may also play a complementary role in appendicitis assessment when integrated into structured diagnostic models.

Statistical analysis

Normality of data distribution was assessed using the Kolmogorov–Smirnov test. Patients were classified into groups with either confirmed or excluded acute appendicitis. Differences between the two groups were evaluated with the Mann–Whitney test for continuous variables and Fisher’s exact test for categorical variables. Diagnostic accuracy metrics—sensitivity, specificity, positive predictive value, negative predictive value, and positive and negative likelihood ratios—were derived from 2×2 contingency tables. Logistic regression analysis was performed to evaluate if the CRP concentrations and urine test strip results were significant predictors of acute appendicitis, among other laboratory parameters already included in the Alvarado score. Statistical analyses were conducted using MedCalc Statistical Software version
16.2.0 (MedCalc Software bvba, Ostend, Belgium). A p-value of <0.05 was considered statistically significant.

Results

Comparison of basic demographic characteristics, as well as clinical and laboratory parameters between groups of patients with and without appendicitis was described in details in the previously published article that addressed the first objective of the prospective study (9). The comparison of additional laboratory parameters (urine test strip analysis and CRP) between groups of patients with and without appendicitis is shown in Table 3. CRP was significantly higher in acute appendicitis groups (68.0 vs 6.0 mg/L, P<0.0001). The comparison of proportions of positive findings of the urinalysis between groups revealed no statistically significant difference (P=0.2813).

Table 4.

The logistic regression on the entire group of patients revealed significance of all four included laboratory variables. However, when dividing patients according to gender, positive urine test strip remained statistically significant only in the group of male patients (Table 4). CRP, although significant in the whole group of selected patients, lost its significant in subgroups of patients stratified according to gender.

Table 5.

Considering the fact that urine test strip addition revealed significant in male subgroup of patients, a diagnostic accuracy study was performed for classical Alvarado scoring system and for a newly proposed scoring system including urinalysis. The comparison of diagnostic accuracy metrics is shown in Table 5.

Discussion

In this prospective study, we evaluated whether the addition of urinalysis could improve diagnostic accuracy for acute appendicitis beyond the parameters included in the traditional Alvarado score. Although the presence of blood and/or leukocytes on urine test strip analysis did not differ significantly between groups of patients with confirmed/rejected diagnosis of acute appendicitis, the logistic regression revealed the urine test strip analysis as a statistically significant negative variable in predicting acute appendicitis. While microscopic hematuria or pyuria can theoretically occur due to irritation of the ureter or bladder by an inflamed appendix (10), these findings

are nonspecific and commonly seen in urinary tract infections or other causes of abdominal pain (11). As such, urinalysis has traditionally been used more as a tool to exclude urinary tract pathology (12) rather than to confirm appendicitis, which could explain the observed negative correlation. Interestingly, our gender-stratified logistic regression analysis showed that a negative urine dipstick result remained a significant predictor only among male patients. The inclusion of urinalysis increased specificity in diagnosis of acute appendicitis, however the sensitivity was being reduced. This finding may reflect gender-specific differences in the prevalence of alternative diagnoses (13).

Women more frequently present with gynecological or urinary conditions that can produce positive urine dipstick results, potentially obscuring any association with appendicitis (14). In contrast, men have fewer common alternative causes of abnormal urinalysis, which may make positive findings more specific in this subgroup. Although this observation is clinically relevant, it should be interpreted with caution, as it may be influenced by sample size and requires further validation in larger cohorts. As recommended by Kollias et al., further research should evaluate the influences that can predict postoperative outcomes following appendectomies between sexes and how to prevent/reduce their occurrence as it has been shown that women had a higher rate of negative appendectomies (13, 15).

Consistent with existing literature, CRP was significantly elevated in patients with appendicitis, reinforcing its role as a useful inflammatory marker in the diagnostic workup (16). However, as we already showed in our preliminary pilot study (8), the logistic regression did not identify CRP concentration as a significant contributor to the acute appendicitis diagnosis in our study, when stratified into subgroups according to gender. Perhaps the underlying cause includes the same information that WBC and CRP offer, and thus one variable becomes redundant. It is worth mentioning that CRP spanned up to remarkably high 416 mg/L in the group of patients without the diagnosis of acute appendicitis, while some acute appendicitis patients had normal CRP values. The observed is in line with the study performed by Atema et al. Who concluded that no WBC count or CRP level can safely and sufficiently confirm or exclude the suspected diagnosis of acute appendicitis in patients who present with abdominal pain of 5 days or less in duration (17). Hallan et al. cautions that CRP is a test of „medium accuracy“ with significant variability accross studies (18). Critically, Shakhatreh et al. Concluded that while CRP is helpful, it does not replace clinical surgical expertise (19). The test is most valuable as a complementary diagnostic tool, not a standalone diagnostic method.

Incorporating urinalysis into a modified scoring system may support more precise clinical decision-making and help reduce unnecessary imaging and surgery, although further validation in larger multicenter cohorts is required.

The strengths of our study include its prospective design, the inclusion of consecutive patients evaluated by the same surgeon, and the independent assessment of clinical decision-making without influence from scoring systems. These features reduce selection bias and increase internal validity. However, several limitations should be acknowledged. First, this was a single-center study, which may limit generalizability. Second, the number of patients within gender subgroups may not have been sufficient to fully assess interaction effects. Third, urine dipstick analysis, while rapid and inexpensive, lacks the precision of microscopic urinalysis or urine culture, which might have provided additional insight.

Future studies should focus on validating the newly proposed scoring system incorporating urinalysis in larger, multicenter cohorts. The ultimate goal remains the development of accurate, practical tools that support timely decision-making while minimizing unnecessary imaging and surgery.

Reference

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