Caprini score is a poor model for predicting risk of thromboembolic events in patients undergoing urethroplasty

Introduction

Within the perioperative period, thrombotic complications such as deep venous thrombosis (DVT) and pulmonary embolism (PE) are dreaded complications of any surgical procedure. They increase morbidity, length of hospital stays, healthcare costs, and overall mortality (1,2). Thus, a common model to risk stratify patients for thromboembolic complications is the Caprini venous thromboembolism (VTE) risk assessment model. The Caprini score is a summation of a variety of patient factors (age, comorbidities, smoking history) and procedural characteristics (length, anesthesia use) (3). Additionally, many hospital systems use the Caprini score to assess quality of care metrics for providers.

Patients undergoing urethroplasty are placed in the lithotomy or high lithotomy position for an extended period, which compresses microvasculature, impairs venous return, and creates venous stasis that theoretically may increase the risk for embolic events (4,5). These urologic patients often have additional risk factors for thrombosis and therefore tend to have moderate to high Caprini scores (6).

Despite this, multiple retrospective studies have demonstrated that the rates of thrombotic events in urethroplasty have been low (7,8). Given these reports in the literature, we sought to describe the risk factors for our cohort of patients undergoing urethroplasty using the well accepted 2005 Caprini score model and report the number of patients in our database with a thrombotic event(s). This study aims to assess the risk of VTE in this patient population using the Caprini risk score, evaluate the incidence of thrombotic events, and determine the score’s applicability to this group. We present this article in accordance with the STROBE reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-634/rc).

Methods

This is a single center, retrospective cohort study. Patients were identified from an institutional review board approved database who underwent urethroplasty by a single surgeon at our institution between the years of 2019–2024. All patients included in the study were males with an age range of 14 to 91 years. Patients who only underwent meatoplasty or extended meatotomy were excluded given the short duration and outpatient nature of these procedures. While operative times were not directly recorded, the average operative time for a urethroplasty at our institution, as calculated by our electronic medical record, is 90 minutes. However, this may somewhat underestimate the average operative time in this cohort as the procedure code used to calculate this time also includes patients who underwent simple, outpatient urethral procedures which were excluded from our study. For bulbar or more proximal urethral strictures, patients are routinely placed in the high lithotomy position (Figure 1). Sequential compressive devices (SCDs) are used unless contraindicated. Patients typically stay for a 23-hour observation after surgery, are not routinely placed on chemical prophylaxis, and must ambulate prior to discharge. If they stay past the 23-hour observation period, they are started on subcutaneous heparin or enoxaparin. While we did not collect the number of patients who stayed past 23 hours, we estimate this to be <5% of our cohort, given this is exceedingly uncommon at our institution.

Figure 1 High lithotomy position.

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the University of Oklahoma Health Sciences Center Institutional Review Board (#11377), and individual consent for this retrospective analysis was waived.

Statistical analysis

During individual chart review, patient risk factors such as age, body mass index (BMI), previous myocardial infarction, malignancy, previous DVT/PE, and numerous other factors outlined by the 2005 Caprini score were recorded in a spreadsheet (9). The spreadsheet modeled the most widely validated 2005 Caprini scoring system through basic arithmetic functions and each result was hand checked with the Caprini VTE MDcalc online resource.

There were several key assumptions in our model:

• No patient was under restricted mobility (0 points).
• Type 2 diabetes mellitus of any kind was tabulated as an extra risk factor.
• BMI >40 kg/m² was counted as being overweight (BMI >25 kg/m²) but also as an additional risk factor (2 points).
• Urethroplasty was designated as major surgery for all (2 points).

The summation of all points for a patient’s age, relevant past medical history, and other VTE risk factors comprised a patient’s individual Caprini risk score, which could then be stratified into designated categories. We captured any thrombotic events that happened within the 90-day postoperative period.

It is worth noting that there is significant heterogeneity in Caprini risk categories within medical literature. While the original model was grouped into three categories (low, moderate, and high), subsequent revisions from 2005 through 2013 added a fourth category, highest risk. Despite this, studies evaluating the utility of the Caprini score within specific patient populations have included anywhere from two to five risk categories, all with differing cutoff scores for each category with the goal to tailor risk categories for each patient population (10). In effort to maintain consistency, we categorized our cohort using the categories outlined by the traditional Caprini model, with Caprini scores >5 described as highest risk.

Results

Of 243 patients examined for eligibility, there were 222 eligible patients included in this study. The median age was 51 years (range 14–91 years with a slight leftward skew). The average BMI was 31.5. In our patient population, 54% were obese, 24% had a history of smoking, 10% had a history of cancer, and only 1 patient had a previous history of PE. A total of 91.9% of patients were placed in the dorsal lithotomy position, while the remainder were supine. The median stricture length was 2 cm (range, 0.5–15 cm, with a bimodal distribution of 1–2 and >4 cm strictures). The most common stricture etiology was idiopathic, followed by iatrogenic, which included both post-procedural following prior transurethral surgeries and traumatic Foley catheter placement. Patients categorized as congenital had hypospadias repairs as children with subsequent stricture formation in adolescence or adulthood. Further surgical details are outlined in Table 1.

Of the 222 patients analyzed, the average Caprini risk score was 4.78, which is between high risk (Caprini score 3–4, 0.97% risk of VTE) and highest risk (score 5–6, 1.33% risk of VTE) according to risk categories outlined in the 2005, 2010, and 2013 updates with the Caprini risk assessment module (11). The most common risk factors in our cohort leading to increased risk score were age, obesity, smoking history, type 2 diabetes mellitus, and history of malignancy. There were 37.8% of patients who were at high risk and 55.0% of patients at highest risk, with Caprini scores >5. Classification of our cohort into Caprini risk categories is displayed in Table 2. We recorded one patient who experienced a thrombotic event (PE) within the 90-day postoperative period who underwent dorsal buccal grafting of a penile stricture in the supine position. He had a high risk Caprini score of 3.

Discussion

Thrombotic complications are a significant concern during the perioperative period, prompting many institutions to utilize the Caprini Risk Assessment Model to guide chemoprophylaxis management, yet it is not clear that this has great applicability within the population of patients undergoing urethroplasty. In our database of 222 patients with varying rates of diabetes mellitus, smoking history, and malignancy history, there was only one patient who experienced a thrombotic event. According to calculated Caprini VTE scores, 55% of patients were designated as having “highest risk” of VTE, though none of these patients had an embolic event. The single patient who formed a VTE had a Caprini score of 3 and was designated as high risk, though he had a penile stricture and was not placed in the high lithotomy position. Other studies have also found similar results in VTE with patients undergoing urethroplasty, though patients in these studies are heterogeneous in administration of chemoprophylaxis (7,12). For example, a 2022 study of 345 patients undergoing urethroplasty found only one patient who had a postoperative VTE, for an overall VTE rate of 0.29%. This patient had an estimated Caprini score <5 and thus did not receive chemoprophylaxis. Of note, patients who did receive chemoprophylaxis in this study did have significantly higher rates of perioperative bleeding complications (12). While the incidence of bleeding requiring reoperation is estimated to be very low following urethroplasty (<0.5%), chemoprophylaxis has been shown to significantly increase this risk in other major surgeries, warranting a cautious risk and benefit consideration in the urethroplasty population (13,14).

Based on this study and its extremely low rate of thromboembolic events, concurrent with other literature, the Caprini risk model appears to be an overestimation of risk for VTE in patients undergoing urethroplasty. However, it is evident from this cohort that overall, thromboembolic events in patients undergoing urethroplasty are extremely rare, despite 92.8% of patients being categorized as high or highest risk. In this cohort, one patient had a VTE event, for an overall VTE rate of 0.45%. He was not in the lithotomy position during surgery. His Caprini score was 3, with a reported associated 0.97% risk of VTE.

This is clinically relevant as hospital systems often use Caprini scores as quality metrics to help dictate care regarding VTE prophylaxis. As outlined by Wilson et al. in Tab. 3 of their study, recommendations for prophylaxis based on the Caprini score indicate that patients with Caprini scores 5–8 receive 7–10 days of chemoprophylaxis and those with scores ≥9 receive 30 days of chemoprophylaxis, regardless of duration of hospitalization (9). Based on our findings, this would have resulted in 55% of the patients being treated with anticoagulation at home while none of them formed a VTE, leading to overtreatment and possible adverse events. Further, the single patient in our cohort with a VTE had a Caprini score of 3 and would not have met the criteria for chemoprophylaxis upon hospital discharge based on this stratification.

Data from literature within other surgical subspecialties have similarly shown limited applicability of the Caprini score in certain populations (15-19). A recent review by Swanson notes that despite recommendations that plastic surgery patients deemed high risk by Caprini score receive postoperative enoxaparin, the data suggest that there is no significant difference in risk for those who received prophylactic anticoagulation (16). Specifically, a 2011 study evaluating thromboembolism risk in plastic surgery patients found no significant difference in rates of VTE in patients who received postoperative enoxaparin compared to those who did not when stratifying by Caprini score alone, even in patients with Caprini scores >8 (17). Further, a meta-analysis evaluating the role of DVT prophylaxis in hospitalized plastic surgery patients found no significant difference in rates of VTE in anticoagulated patients when stratified by Caprini score but did find an increased rate of bleeding requiring reoperation (18). Within orthopedic surgery, a 2020 study evaluating over 2,000 patients who underwent primary hip or knee arthroplasties found no significant difference in VTE rates for patients with higher Caprini scores, determining Caprini scores alone do not have the predictive power to guide treatment in this population (19). Within urologic literature, a study by Habashy et al. showed the Caprini risk score to be quite high in patients undergoing inflatable penile prosthesis surgery, yet a large study of over 21,000 men undergoing artificial urinary sphincter and inflatable penile prosthesis surgery showed the VTE rate to be just over 1% (20,21). Another study evaluated over 65,000 patients who had undergone major abdominal or pelvic urologic surgery and found that Caprini score alone was not predictive of VTE risk. Within this study, the rate of VTE following radical cystectomy was found to be over double that of other surgeries; however, even within this subset of patients, VTE risk was found to be independent of Caprini risk category (22).

This study has several limitations. First, we have a small sample size, especially given the low rate of VTE in this group, though it is consistent with other similar studies in this population. It is also inherently limited by its retrospective nature. For instance, it is possible that relevant risk factors could have been missed in history intake, possibly underestimating the Caprini score that could have been more accurately calculated in a prospective study. Additionally, it is limited by its single institution nature. Despite this, given the diversity in patient age, stricture etiology, and repair approach, we feel this study is generalizable to represent the larger urethroplasty population.

To our knowledge, this is the first study to model the utility of the Caprini risk assessment model in patients who underwent urethroplasty and report calculated scores and number of VTE in the 90-day perioperative period in relation to this. We feel our study provides value in that it questions a widely accepted quality control metric, which does not appear to have any applicability to the urethroplasty patient population. Further research will be necessary to prospectively evaluate the risk for and incidence of thrombotic events, identify an algorithm to more appropriately quantify VTE risk, and determine the need for chemical prophylaxis in patients undergoing urethroplasty.

Conclusions

Despite the success of the Caprini score in quantifying thromboembolic risk in hospitalized patients, there does not appear to be good applicability for patients undergoing urethroplasty. Further research will be necessary to prospectively evaluate the risk for and incidence of VTE, as well as the indications for perioperative chemical prophylaxis in this population.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-634/rc

Data Sharing Statement: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-634/dss

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-634/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-2025-634/coif). The 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 University of Oklahoma Health Sciences Center Institutional Review Board (#11377), 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/.

References

1. Nielsen VG, Asmis LM. Hypercoagulability in the perioperative period. Best Pract Res Clin Anaesthesiol 2010;24:133-44. [Crossref] [PubMed]
2. Gordon RJ, Lombard FW. Perioperative Venous Thromboembolism: A Review. Anesth Analg 2017;125:403-12. [Crossref] [PubMed]
3. Caprini JA. Thrombosis risk assessment as a guide to quality patient care. Dis Mon 2005;51:70-8. [Crossref] [PubMed]
4. Hirshberg A, Mattox KL. Vascular trauma. Haimovici H. In: Ascher E, Hollier LH, Strandness DE, et al. editors. Haimovici’s vascular surgery. 5th ed. Wiley; 2004:421-36.
5. Angermeier KW, Jordan GH. Complications of the exaggerated lithotomy position: a review of 177 cases. J Urol 1994;151:866-8. [Crossref] [PubMed]
6. Zhu L. Analysis of Related Risk Factors for Deep Vein Thrombosis after Urology Surgery. Frontiers in Medical Science Research 2022;4:47-51.
7. Moynihan MJ, Vanni AJ. Risk of Post-Operative Venous Thromboembolism in Urethroplasty. New England Section of the American Urological Association. Hartford: September 7, 2018.
8. Lee HH, Shaw NM, Hays E, et al. Do no harm: the role of perioperative heparin in urethroplasty. Int Urol Nephrol 2022;54:2181-6. [Crossref] [PubMed]
9. Wilson S, Chen X, Cronin M, et al. Thrombosis prophylaxis in surgical patients using the Caprini Risk Score. Curr Probl Surg 2022;59:101221. [Crossref] [PubMed]
10. Hayssen H, Cires-Drouet R, Englum B, et al. Systematic review of venous thromboembolism risk categories derived from Caprini score. J Vasc Surg Venous Lymphat Disord 2022;10:1401-1409.e7. [Crossref] [PubMed]
11. Caprini JA. Risk assessment as a guide to thrombosis prophylaxis. Curr Opin Pulm Med 2010;16:448-52. [Crossref] [PubMed]
12. Shaw NM, Hakam N, Lui JL, et al. Incidence of venous thromboembolism in benign urologic reconstructive cases. World J Urol 2022;40:1879-86. [Crossref] [PubMed]
13. Tikkinen KAO, Craigie S, Agarwal A, et al. Procedure-specific Risks of Thrombosis and Bleeding in Urological Non-cancer Surgery: Systematic Review and Meta-analysis. Eur Urol 2018;73:236-41. [Crossref] [PubMed]
14. Anderson DR, Morgano GP, Bennett C, et al. American Society of Hematology 2019 guidelines for management of venous thromboembolism: prevention of venous thromboembolism in surgical hospitalized patients. Blood Adv 2019;3:3898-944. [Crossref] [PubMed]
15. Keyes GR, Singer R, Iverson RE, et al. Incidence and Predictors of Venous Thromboembolism in Abdominoplasty. Aesthet Surg J 2018;38:162-73. [Crossref] [PubMed]
16. Swanson E. Reconsidering the value of Caprini scores and venous thromboembolism (VTE) risk mitigation methods in plastic surgery patients. Aesthetic Plast Surg 2023;47:223-7. [Crossref] [PubMed]
17. Pannucci CJ, Dreszer G, Wachtman CF, et al. Postoperative enoxaparin prevents symptomatic venous thromboembolism in high-risk plastic surgery patients. Plast Reconstr Surg 2011;128:1093-103. [Crossref] [PubMed]
18. Pannucci CJ, MacDonald JK, Ariyan S, et al. Benefits and Risks of Prophylaxis for Deep Venous Thrombosis and Pulmonary Embolus in Plastic Surgery: A Systematic Review and Meta-Analysis of Controlled Trials and Consensus Conference. Plast Reconstr Surg 2016;137:709-30. [Crossref] [PubMed]
19. Gold PA, Ng TY, Coury JR, et al. Can the Caprini score predict thromboembolism and guide pharmacologic prophylaxis after primary joint arthroplasty? J Orthop 2020;21:345-9. [Crossref] [PubMed]
20. Habashy E, Hebert K, Helo S, et al. Caprini Risk Score is Shockingly High in Penile Prosthesis Surgery Patients. J Sex Med 2022;19:S55-6.
21. Hebert KJ, Matta R, Horns JJ, et al. Risk of Postoperative Thromboembolism in Men Undergoing Urological Prosthetic Surgery: An Assessment of 21,413 Men. J Urol 2022;208:878-85. [Crossref] [PubMed]
22. McAlpine K, Breau RH, Mallick R, et al. Current guidelines do not sufficiently discriminate venous thromboembolism risk in urology. Urol Oncol 2017;35:457.e1-8. [Crossref] [PubMed]