Abstract: 【Abstract】 Objective To evaluate the application value of peripheral blood serum fibronectin in combination with non-treponemal antibody testing in predicting asymptomatic neurosyphilis. Methods A retrospective analysis was conducted on 74 syphilis inpatients in the serofast state at the Affiliated Infectious Diseases Hospital of Soochow University from February 2019 to October 2022. According to the guidelines for the diagnosis and treatment of syphilis（2020 version）, the patients were divided into an asymptomatic neurosyphilis group （17 cases） and a non-neurosyphilis group （57 cases）. The differences in serum fibronectin levels and non-specific antibody titers detected by the toluidine red unheated serum test （TRUST） were analyzed between the two groups. Skewed data were presented as M （Q1, Q3）, and receiver operating characteristic （ROC） curves were plotted to establish a binary logistic regression model. Results In the non-neurosyphilis group, there were 25 males and 32 females, aged 22 to 76 years; in the asymptomatic neurosyphilis group, there were 10 males and 7 females, aged 26 to 66 years. There were no significant differences in the gender and age distribution between the two groups （both P > 0.05）. The serum fibronectin levels （486.0 ［387.5, 605.0］ mg/L） and serum non-specific antibody titers （base-2 logarithmic transformation ［-log2 titer］ : 5 ［4, 6］） in the asymptomatic neurosyphilis group were both significantly higher than those in the non-neurosyphilis group （410.0 ［347.5, 474.5］ mg/L, 3 ［1, 4］, Z = 2.36, 4.43, respectively, both P < 0.05）. The areas under the ROC curves of serum fibronectin alone, non-treponemal antibody titers alone, and the two indicators in combination for the diagnosis of asymptomatic neurosyphilis were 0.689 （95% CI: 0.540 -0.838）, 0.850 （95% CI: 0.757 - 0.942）, and 0.878 （95% CI: 0.787 - 0.970） respectively. Binary logistic regression analysis showed that serum fibronectin levels and non-treponemal antibody titers were associated with the occurrence of asymptomatic neurosyphilis in serofast syphilis patients （both P < 0.05）. Based on the binary logistic regression analysis, a model equation was obtained as follows: Logit （P） = 0.008 × serum fibronectin levels + 0.090 × reciprocal titers of serum non-treponemal antibodies - 6.483, when the Logit （P） ≥ -0.703, it suggested a high probability of asymptomatic neurosyphilis. The cut-off value with 100% sensitivity and the highest specificity was selected, and the probability of patients having asymptomatic neurosyphilis was 0 when the Logit （P） ≤ -2.863. According to the above new prediction model, asymptomatic neurosyphilis could be excluded in 19 （25.68%） patients with serofast syphilis. Conclusion The combination of serum fibronectin with non-treponemal antibody titers showed certain diagnostic value among patients with serofast syphilis, which could help predict and exclude some patients with serofast asymptomatic neurosyphilis.

Key words: Neurosyphilis, Syphilis serofast, Diagnosis, Asymptomatic neurosyphilis, Fibronectin, Toluidine red unheated serum test, Prediction model