Mean platelet volume is a predictor for abscess formation in patients with epididymitis

Introduction

Epididymitis, an inflammatory process involving the epididymis, can occur at any age. When epididymitis occurs with the adjacent testicle, it is called epididymo-orchitis. So far, the accurate prevalence of epididymitis is still unknown since it is not effectively coded in different settings, such as the outpatient or emergency department setting. The annual incidence was approximately 600,000 new cases in the United States in 2002 (1). Recent data from Australia suggest that the prevalence of epididymitis increased between 2009 and 2014; in admissions, it increased from 28.3 to 38.7 per 100,000 men and in emergency departments from 64.8 to 91.9 per 100,000 men (2). Scrotal pain and swelling can be noted in most cases, with or without concurrent symptoms of dysuria, frequency, urgency, fever, chills and nausea (3).

Infectious and noninfectious processes may lead to epididymitis, but bacterial infections are the most common aetiology. Treatment guidelines based on the evidence of available antimicrobial trials have been developed (4,5). Prompt medication against the underlying pathogens is important in managing epididymitis, eradicating the infection, relieving symptoms, and preventing complications. Delayed treatment could result in the progression of epididymitis, leading to serious sequelae such as abscess formation, testicular atrophy, infarction, and potentially infertility.

Abscess formation is a relatively rare complication of epididymitis, with a reported incidence of 3.3% (2). It increases the need for surgical interventions, including abscess incision and drainage, epididymectomy, and orchiectomy. Moreover, it may lead to a significant rise in infertility among men of childbearing age. Ultrasound examination is an effective method for determining whether an abscess has developed. However, its utility in predicting abscess formation is limited. Therefore, it is essential to find a rapid and convenient forecasting method.

Complete blood count (CBC) is a rapid, economical, and convenient method for detecting inflammation in clinical practice. Nowadays, CBC parameters such as mean platelet volume (MPV), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), neutrophil-to-monocyte ratio (NMR), and mean platelet volume-to-lymphocyte ratio (MPVLR) have been widely used to explore disease progress and clinical outcomes (6-8). In the present study, we aimed to show the predictive value of these haematologic parameters in adult epididymitis patients with abscess formation. We present this article in accordance with the STROBE reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-436/rc).

Methods

Source of data

The Clinical Data Analysis and Reporting System (CDARS), a population-based database documenting key demographics, diagnoses, procedures, and medication records of patients attending public hospitals and clinics in Hong Kong, was used for data collection. CDARS encodes diagnoses using the International Classification of Diseases, ninth revision (ICD-9) codes and epididymitis encodes 604.9, and epididymitis with abscess formation 604.0. The diagnosis of epididymitis with abscess formation was typically as follows: patients were examined clinically for any signs suggestive of abscess formation (such as fluctuation), and for those suspected, an ultrasound examination was performed to confirm the clinical diagnosis before proceeding to surgical treatment. Superior coding accuracy of this database and use for conducting epidemiological studies have been extensively proven in our previous study (9-11). The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Joint Chinese University of Hong Kong-New Territories East Cluster Clinical Research Ethics Committee (No. 2025.561) and individual consent for this retrospective analysis was waived.

Patient population

Adult patients (aged >18 years) with epididymitis between January 2000 and December 2024 were included. To reduce potential biases, the following patients were excluded: (I) those who recently received immunosuppressive therapy; (II) individuals with a history of severe malignant tumours or immune system diseases; and (III) patients with incomplete clinical data. The patients were divided into two groups: epididymitis alone and epididymitis with abscess formation. Patients diagnosed with both epididymitis and epididymitis with abscess formation during the same period were counted only in the latter group.

Variables collected

Demographic data were collected, including age and comorbidities that may affect the prevalence of epididymitis, such as diabetes mellitus, tuberculosis, and prior prostate surgery. The CBC was performed at the initial clinical encounter and repeated during treatment monitoring. CBC tests report neutrophils, lymphocytes, monocytes, platelets, eosinophils, basophils and MPV, while NLR, PLR, NMR, and MPVLR were calculated as CBC-derived inflammatory biomarkers. The CBC results obtained during the first patient visit were extracted for analysis.

Statistical analyses

Measurement data conforming to a normal distribution were expressed as the mean ± standard deviation, and a t-test was employed to compare data between groups. Measurement data not conforming to a normal distribution were presented as the median (interquartile range), and the Mann-Whitney U test was utilised to compare data between groups. The Chi-squared test or Fisher’s exact test was employed for categorical variables. After excluding multicollinearity among independent variables and assessing model fitness using the variable inflation factor (VIF) and the Hosmer-Lemeshow model fitness test, logistic regression was applied to identify predictive factors for epididymitis patients with abscess formation. All independent variables were included in univariate logistic regression analysis. Subsequently, those independent variables with a P value <0.05 in the univariate logistic regression analysis were subjected to multivariate logistic regression analysis. The discriminative power was evaluated through receiver operating characteristic (ROC) curve analysis. All statistical analyses were conducted using version 27.0 of SPSS software (IBM Corp, Armonk, NY, USA), and a P value of less than 0.05 was regarded as statistically significant.

Results

Study cohort

From January 2000 to December 2024, 8,540 adult patients with epididymitis were identified. Patients whose CBC parameters may be affected by recent immunosuppressive therapy (n=36), or by a history of severe malignant tumors or immune system diseases (n=559), and those with incomplete clinical data (n=3,255) were excluded. Ultimately, 4,652 were included in the final analysis (Figure 1), of whom 4,567 (mean age 54.2±20.0 years) had epididymitis, while 85 (mean age 65.9±17.3 years) had epididymitis with abscess formation. Table 1 presents demographic data, as well as results from CBC and CBC-derived inflammatory biomarkers. Those who ultimately underwent epididymectomy or orchiectomy were identified, revealing that the rate of these procedures in the group with epididymitis and abscess formation was significantly higher than that in the epididymitis group (34/85 vs. 65/4,567, P<0.001) (Figure 2).

Figure 1 Flowchart of the study.

Figure 2 Number of epididymectomy or orchiectomy between epididymitis and epididymitis with abscess formation groups. ***, P<0.001.

Logistic regression analysis

Firstly, VIF tests were conducted. All variables were below the threshold (VIF <10), indicating that no multicollinearity exists among the independent variables (Table S1). Subsequently, multivariate logistic regression analysis was carried out, revealing that age [OR =1.037, 95% confidence interval (CI): 1.023–1.051], history of diabetes mellitus (OR =4.400, 95% CI: 2.673–7.243), and MPV (OR =1.886, 95% CI: 1.570–2.267) were independent predictors for epididymitis with abscess formation (Table 2). The model adequacy was assessed using the Hosmer–Lemeshow goodness-of-fit test (P=0.64).

ROC analysis

ROC curve analysis revealed that MPV could effectively predict adult epididymitis patients with abscess formation. The area under the ROC curve (AUC) was 0.713 (95% CI: 0.650–0.777), with a sensitivity of 63.5% and specificity of 75.5%. The cutoff value for MPV was 8.80 fL. When assessed in combination with age and diabetes mellitus, the accuracy improved significantly, with an AUC of 0.828 (95% CI: 0.788–0.868), a sensitivity of 68.2%, and a specificity of 82.2% (Figure 3).

Figure 3 Receiver operator curves of MPV, age and diabetes mellitus. *, the cutoff value for MPV was 8.80 fL. The area under the receiver operating characteristic curve was 0.713, with a sensitivity of 63.5% and specificity of 75.5%. DM, diabetes mellitus; MPV, mean platelet volume.

Subgroup analysis

Further analysis of MPV and epididymitis within specific subgroups based on age, diabetes mellitus, prior prostate surgery, and tuberculosis was examined. No significant interaction effects were found between MPV and these subgroups (P value for interaction >0.05). The results of subgroup analyses are summarized in Figure 4.

Figure 4 Subgroup analysis. CI, confidence interval; MPV, mean platelet volume; OR, odds ratio.

Discussion

To the best of our knowledge, this is the first study exploring the predictive value of CBC parameters in adult patients with epididymitis and abscess formation. Our primary findings revealed that, among various haematologic parameters, MPV was an independent predictor for epididymitis with abscess formation. Furthermore, for epididymitis patients who are older and have diabetes mellitus, greater attention should be given to the possibility of abscess formation when MPV is >8.80 fL.

Epididymitis is a common inflammatory disease in outpatients or emergency departments settings. Clinically, prompt treatment and follow-up can lead to a good prognosis among most patients. Empirical antimicrobial therapy should be initiated immediately after clinically diagnosing a patient with acute epididymitis, and subsequent adjustments to the treatment regimen may be required once the specific pathogen is identified and antibiotic susceptibility data are obtained (12). The duration of antibiotic therapy is 10–14 days, accompanied by a follow-up visit within 1–2 weeks to evaluate the clinical response to treatment (5,13,14). Inflammation parameters, ultrasonography, and microbial cultivation are recommended for diagnosis and evaluation (3,5). However, under different circumstances, in outpatient or emergency department settings, ultrasonography and microbial cultivation are time-consuming and not always readily available (15). CBC is a rapid, economical and convenient method for detecting inflammation in clinical practice. So far, numerous investigations have explored the value of CBC parameters in various inflammatory diseases (7,16-18).

For acute scrotum, previous studies mainly focus on the role of CBC parameters in differentiating epididymitis from testicular torsion since testicular torsion is an acute scrotal pathology that requires urgent surgical intervention. NLR was identified as being able to be adopted in diagnosing testicular torsion with a cut-off of 2.5 (15). In a systematic review and meta-analysis, NLR was considered a beneficial parameter for differential diagnosis between epididymitis and testicular torsion (19). Another valuable parameter is MPV, which has been demonstrated to be used as an adjuvant parameter in the diagnosis and differential diagnosis of testicular torsion (20-22). Furthermore, the MPV may be clinically useful in predicting organ salvage for patients with testicular torsion (23).

Epididymitis with abscess formation, similar to testicular torsion, also encounters an increased risk of organ loss compared to epididymitis. Our results showed that 40% (34/85) of epididymitis patients with abscess formation underwent epididymectomy or orchiectomy, significantly higher than that of epididymitis patients (1.4%, 65/4,567). For epididymitis patients with abscess formation, they are more prone to developing fever, chills, and in severe cases, bacteremia may even occur. This condition falls under the category of systemic infection according to the new European Association of Urology classification of urinary tract infections (24). It necessitates a more thorough diagnostic assessment and treatment approach, encompassing blood culture tests, imaging studies (like ultrasound or cross-sectional imaging techniques), intravenous administration of antimicrobial agents, and potentially hospitalization for enhanced surveillance and more intensive medical management. In this study, MPV was indicated as a valuable predictor of adult epididymitis patients with abscess formation among the hematologic parameters. MPV, a parameter that measures the average size of platelets, indicates platelet production and activation (25). Research showed that it’s changed by cytokines such as interleukin (IL)-1 and IL-6 through the viscoelastic properties, leading to platelet hyper-activation and spreading (26). An elevated level of MPV, reflecting more active metabolically and enzymatically platelets, can contribute to severe inflammatory response (27). Studies have shown that MPV levels are higher in acute appendicitis cases compared to negative cases. Furthermore, in complicated appendicitis, such as with abscess formation or gangrene, MPV is significantly elevated (28,29). In this study, MPV was markedly higher in epididymitis cases with abscess formation than those without (9.10 vs. 8.10, P<0.001), suggesting that MPV correlates with increased inflammation severity.

Notably, the current study also showed that age and diabetes mellitus were associated with abscess formation in epididymitis patients. The aetiology of epididymitis is thought to be highly dependent on age. For adults <35 years old, sexually active should be first taken into consideration, while the retrograde flow of infected urine is the most common cause for those older than 35 years (13). Thus, treatments, to some extent, differ for different ages. Diabetes mellitus heightens vascular inflammation and oxidative stress whilst elevating platelet activity, accelerates the development of thrombosis and homeostasis in diabetes mellitus (30). Published studies have demonstrated that elevated MPV is a risk factor for diabetes mellitus (31-33). Although the subgroup analysis of this study indicated that MPV was elevated in epididymitis patients with abscess formation across all age groups and in diabetic patients, no interaction effects were found between MPV and age or diabetes mellitus. When MPV was assessed alongside age and diabetes mellitus, the predictive accuracy for abscess formation in epididymitis patients increased significantly. Therefore, for patients with these clinical or laboratory features, managing physicians should be vigilant about the potential for abscess formation in older epididymitis patients with diabetes mellitus. At the same time, these high-risk patients require close follow-up and extended antibiotic therapy.

Several limitations of the current study must be acknowledged. First, selection bias and residual confounding cannot be dismissed due to its retrospective nature. Second, the low incidence and exclusion criteria led to a limited number of epididymitis patients with abscess formation included in this study. However, to our knowledge, this represents one of the observational studies with the largest sample size. Third, this study utilized a representative population-based database covering up to 94% of all secondary and tertiary healthcare services in Hong Kong. Nevertheless, this also restricted the inclusion of some laboratory tests and specific inflammatory parameters, such as HbA1c or blood glucose levels or microbiological data, or C-reactive protein, which were omitted from this study due to insufficient data. Since most patients with epididymitis seek medical care in outpatient or emergency departments, and all diagnoses were made using ICD-9 coding, some comorbidities, such as inflammatory diseases (chronic or acute), might be overlooked in the coding. Fourth, some patients diagnosed with epididymitis who presented for their first visit may have already developed abscesses because of the waiting time for the ultrasound examination. To prevent duplication in coding, those diagnosed with epididymitis and those with epididymitis with abscess formation during the same period were counted only in the latter group. Additionally, a post-hoc analysis was conducted of 22 epididymitis patients with abscess formation who had previously sought medical treatment for epididymitis. The average MPV value of these patients at the time of their visit for epididymitis was 8.97 fL, which exceeds the optimal cut-off value of MPV (8.80 fL). Therefore, this further demonstrates the predictive value of MPV in adult epididymitis patients with abscess formation.

Conclusions

MPV is an independent predictor of epididymitis with abscess formation. In epididymitis patients of advanced age with diabetes mellitus, greater attention should be paid to the possibility of abscess formation when MPV exceeds 8.80 fL.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-436/rc

Data Sharing Statement: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-436/dss

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-436/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-436/coif). C.F.N. serves as an unpaid editorial board member of Translational Andrology and Urology from January 2025 to December 2026. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Joint Chinese University of Hong Kong-New Territories East Cluster Clinical Research Ethics Committee (No. 2025.561) and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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