Abstract
Background
The cerebrospinal fluid (CSF) venereal disease research laboratory (VDRL) test remains the standard for the laboratory diagnosis of neurosyphilis. The toluidine red unheated serum test (TRUST) is an alternative to the VDRL test as a serological test for syphilis, but it lacks guidelines for its use in CSF for neurosyphilis diagnosis.
Methods
A total of 210 suspected neurosyphilis patients were included, consisting of 124 neurosyphilis patients and 86 syphilis/non-neurosyphilis patients. The TRUST was modified into the CSF-TRUST-10 test with 10 μL of antigen by referring to the CSF-VDRL test, and the CSF-TRUST-17 test with 17 μL of antigen by referring to its procedures in serum. The diagnostic performance of the CSF-TRUST-10 and CSF-TRUST-17 tests and the concordance between them and the CSF-VDRL test were evaluated.
Results
The diagnostic performance of the CSF-TRUST-10 and CSF-TRUST-17 tests for diagnosing neurosyphilis were comparable to the CSF-VDRL test, as well as the positive rate. The agreement rate was 98.7% between the qualitative CSF-TRUST-10 and CSF-VDRL tests. A total of 91.4% of the quantitative CSF-TRUST-10 results were consistent with the CSF-VDRL test, and the discordant results were no more than two titres. The agreement rate was 98.1% between the qualitative CSF-TRUST-17 and CSF-VDRL tests and 87.6% between the quantitative CSF-TRUST-17 and CSF-VDRL tests.
Conclusions
The CSF-TRUST with 10 μL of antigen could be an alternative for the CSF-VDRL test for neurosyphilis diagnosis. Our results provide a basis for using the TRUST to guide the diagnosis of neurosyphilis.
Keywords: CSF, TRUST, VDRL, Neurosyphilis, Diagnosis
1. Introduction
Neurosyphilis refers to an infection of the central nervous system by Treponema pallidum, and neurosyphilis can develop at any time during the course of syphilis. Globally, there are about 18 million people infected with T. pallidum [1]. The organism invades the CNS relatively early in the infection in approximately one-quarter of syphilis patients and leaves an estimated 4–9% of patients eventually developing late manifestations of neurosyphilis [2]. The clinical manifestation spectrum of neurosyphilis varies from an asymptomatic state to various neurological symptoms and even death. At present, the cerebrospinal fluid (CSF) venereal disease research laboratory (VDRL) test remains the standard for the laboratory diagnosis of neurosyphilis [3]. The VDRL test is based on an antigen composed of an alcoholic solution containing measured amounts of cardiolipin, cholesterol, and sufficient purified lecithin to measure antibodies to lipoidal material released from damaged host cells as well as to lipoprotein-like material and possibly by cardiolipin released from the treponemes [4]. However, the CSF-VDRL is technically cumbersome, the antigen suspension needs to be freshly prepared, and the results should be read with a light microscope. Thus, the reproducibility of the VDRL method depends on the reagent and the operator. In resource-limited settings, the CSF-VDRL test may not be widely available [5].
The VDRL test has been modified into the rapid plasma reagin test (RPR) and toluidine red unheated serum test (TRUST), in which sized charcoal particles or toluidine red particles are added to the VDRL antigen as markers to achieve direct visual observation of the results of an antigen-antibody reaction [4]. For the diagnosis of syphilis, the RPR test and TRUST are equivalent serologic methods to the VDRL method for serum samples [6,7]. For the diagnosis of neurosyphilis, the CSF RPR has been recommended as an alternative for the CSF-VDRL for neurosyphilis diagnosis [7]. In China, most laboratories perform the TRUST [8]. Lin et al. analyzed data involving 210 HIV-negative neurosyphilis patients and found that the CSF-TRUST had comparable sensitivity (76.2% versus 81.4%) and specificity (93.1% versus 90.3%) to the CSF-VDRL test [9]. Our previous study that included 824 syphilis patients also demonstrated that the overall agreement between the CSF-TRUST and the CSF-VDRL tests was 97.3% (802/824), indicating that the CSF-TRUST could be used as an option for CSF examination in settings without the CSF-VDRL test in place [10].
According to the manufacturer's instructions, the original design of the TRUST was for serum examination using 17 μL of antigen, so there were no guidelines for the operation and interpretation of the CSF-TRUST [11]. An antigen amount of 10 μL used for CSF-VDRL could be available for CSF-TRUST reference [12]. Here, this study aimed to further determine the optimum amount of antigen of the CSF TRUST for the replacement of the CSF VDRL test as a guideline for the diagnosis of neurosyphilis.
2. Methods
2.1. Study population and ethics statement
Between August 2017 and January 2021, a total of 210 patients who attended Zhongshan Hospital of Xiamen University, School of Medicine, Xiamen University, were suspected of having neurosyphilis and underwent lumbar punctures. All of these patients underwent nontreponemal tests and treponemal tests using both serum and CSF. This study was approved by the Ethics Committee of the School of Medicine, Xiamen University (No. 2022-012), and it was conducted in compliance with the national legislation of China and the Declaration of Helsinki guidelines. Written informed consent was obtained from all of the study participants.
2.2. Diagnostic criteria
The diagnostic criteria for neurosyphilis were based on those as described in the guidelines of the Centers for Disease Control in the United States and Europe [6,7]. Briefly, neurosyphilis was defined as syphilis at any stage with a positive T. pallidum particle agglutination (TPPA) assay result based on a CSF sample and a combination of the following findings: (1) reactive VDRL in a CSF sample, (2) clinical symptoms or signs consistent with neurosyphilis without other known causes for these clinical abnormalities, and (3) elevated CSF protein concentration (>500 mg/L) or leukocyte count (>5 cells/μL) in the absence of other known causes of these abnormalities. Verified neurosyphilis was defined as meeting conditions (1) and (2); likely neurosyphilis was defined as meeting conditions (2) and (3); and possible neurosyphilis was defined as meeting condition (2). The above three classifications were all treated as neurosyphilis.
2.3. Laboratory tests
The TRUST (Shanghai Rongsheng Biotech Co., Ltd. Shanghai, China) and TPPA (Fujirebio, Tokyo, Japan) tests in both serum and CSF samples were performed for all participants, as well as the VDRL (Becton, Dickinson Co., Maryland, USA) test in CSF. The serological tests and CSF-VDRL test were performed according to the manufacturer's instructions and as previously reported [13].
There was no standard procedure of the TRUST on CSF. The CSF-TRUST was performed according to that of the serum tests using an 18 mm circle card test. First, 50 μL of the specimen was placed on a plastic-coated card; next, the specimen was spread within the area of the circle; and antigen was added with one drop of antigen. A mechanical rotator was used to mix the antigen and antibody. The mixture was rotated for 8 min at 100 rpm. The quantitative test was performed in a manner comparable to the qualitative test, except that serial twofold dilutions of the samples were prepared in 0.9% saline. The quantitative results were reported as the highest dilution giving a reactive result. In this study, the CSF-TRUST referred to the CSF-TRUST-10 test with 10 μL of antigen or the CSF-TRUST-17 test with 17 μL of antigen. The parameters of the operating procedures of the CSF-VDRL, CSF-TRUST-10 and CSF-TRUST-17 tests are shown in Table 1.
Table 1.
The parameters of the operating procedures of the CSF-VDRL, CSF-TRUST-10, and CSF-TRUST-17 tests.
| CSF-VDRL | CSF-TRUST-10 | CSF-TRUST-17 | |
|---|---|---|---|
| Specimen (μL) | 50 | 50 | 50 |
| Antigen (μL) | 10 | 10 | 17 |
| Reaction circle diameter (mm) | 16 | 18 | 18 |
| Rotation rate (rpm) | 180 | 100 | 100 |
| Rotation duration (min) | 8 | 8 | 8 |
Abbreviations: CSF, cerebrospinal fluid; VDRL, venereal disease research laboratory; TRUST, toluidine red unheated serum test.
In TPPA test, the gelatin particles sensitized with T. pallidum antigen would be combined with the syphilis antibodies and produce agglutination reaction. The results of TPPA test could be visually evaluated because of the magenta color of gelatin particles [14]. The CSF-TPPA test was performed in a manner similar to that of the serum tests. The CSF protein levels were quantified using a Roche Cobas 8000 automatic biochemistry analyzer (Roche Diagnostics, F. Hoffmann La Roche Ltd., Switzerland). The CSF leukocyte counts were measured using an Automatic Blood Cell XE5000 Analyzer (Sysmex International Reagents, Co., Ltd, Japan).
2.4. Statistical analysis
The variables are presented as medians (interquartile range [IQR]) for the continuous variables or frequencies (%) for the categorical variables. The diagnostic performance of the nontreponemal tests was determined and was compared to the results of the diagnostic criteria for neurosyphilis using sensitivity and specificity according to the Yerushalmy model. McNemar's test and McNemar-Bowker test were used to test the difference between correlated proportions on a 2 × 2 classification table and m × m contingency table, respectively [15]. The strength of agreement between the paired groups of binary and ordinal categorical variables was defined according to the kappa and weighted kappa values, respectively, and was classified as almost perfect (κ, 0.81–1.00), substantial (κ, 0.61–0.80), moderate (κ, 0.41–0.60), fair (κ, 0.21–0.40), slight (κ, 0.00–0.20), and poor (κ < 0.00) [16]. All statistical analyses were performed using SPSS 25.0 for Windows (SPSS Inc., Chicago, IL, USA). A two-sided P value of <0.05 was considered statistically significant.
3. Results
3.1. Demographic characteristics of the study population
A total of 210 participants were included in the study, consisting of 124 neurosyphilis patients and 86 syphilis/non-neurosyphilis patients. The neurosyphilis group included 91 (73.4%) males and 33 (26.6%) females, and their median age was 51 (IQR, 38–58) years. The non-neurosyphilis group included 38 (44.2%) males and 48 (55.8%) females, and their median age was 42 (IQR, 30–50) years.
3.2. The diagnostic performance of the CSF-TRUST-10 and CSF-TRUST-17 tests for neurosyphilis
In our study, with the diagnosis of neurosyphilis as the reference standard, the sensitivities of the CSF-VDRL, CSF-TRUST-10, and CSF-TRUST-17 tests were 71.8% (89/124), 66.3% (57/86), and 68.5% (85/124), respectively. There was no significant difference in the pairwise comparison of sensitivity (CSF-TRUST-10 versus CSF-VDRL, P = 0.500; CSF-TRUST-17 versus CSF-VDRL, P = 0.125; CSF-TRUST-10 versus CSF-TRUST-17, P > 0.999) (Table 2). The specificity was 100.0% for the CSF-VDRL, CSF-TRUST-10, and CSF-TRUST-17 tests. In consideration of the differences in sex and age between the neurosyphilis and syphilis/non-neurosyphilis patients, the sensitivity and specificity were further evaluated by a stratification analysis using sex and age, and there was no significant difference (data not shown).
Table 2.
Comparison of the sensitivities and specificities of the CSF-VDRL, CSF-TRUST-10, and CSF-TRUST-17 tests for neurosyphilis diagnosis.
| Sensitivity comparison in neurosyphilis patients (n = 124) |
P1 |
Specificity comparison in syphilis/non-neurosyphilis patients (n = 86) |
P2 |
|||
|---|---|---|---|---|---|---|
| CSF-TRUST-10a | CSF-VDRL |
CSF-VDRL |
||||
| Positive | Negative | Positive | Negative | |||
| Positive | 57 | 0 | 0.500 | 0 | 0 | n.a. |
| Negative | 2 | 27 | 0 | 66 | ||
| CSF-TRUST-17 | CSF-VDRL | CSF-VDRL | ||||
| Positive | Negative | Positive | Negative | |||
| Positive | 85 | 0 | 0.125 | 0 | 0 | n.a. |
| Negative | 4 | 35 | 0 | 86 | ||
| CSF-TRUST-17 | CSF-TRUST-10a | CSF-TRUST-10a | ||||
| Positive | Negative | Positive | Negative | |||
| Positive | 57 | 0 | >0.999 | 0 | 0 | n.a. |
| Negative | 0 | 29 | 0 | 66 | ||
Abbreviation: CSF, cerebrospinal fluid; VDRL, venereal disease research laboratory; TRUST, toluidine red unheated serum test; n.a., not available.
The results of the CSF-TRUST-10 test were missing for 38 neurosyphilis patients and 20 syphilis/non-neurosyphilis patients.
3.3. The concordance between the qualitative CSF-TRUST-10 and CSF-TRUST-17 tests and the CSF-VDRL
As the CSF-VDRL test is in clinical practice, the positive rates of the CSF-TRUST-10 and CSF-TRUST-17 tests were compared. There was no significant difference in the positive rate between the CSF-TRUST-10 test and the CSF-VDRL test (37.5% [57/152] versus 38.8% [59/152], P = 0.500). The positive and negative predictive values of the CSF-TRUST-10 test were 100.0% and 97.9%, respectively. The agreement rate between the two tests was 98.7% (150/152), and the Kappa value was 0.972 (P for κ < 0.001), indicating that the strength of agreement was almost perfect.
In consideration of that the results of the CSF-TRUST-10 test were missed in 27.6% (58/210) of the participants, the distribution of basic characteristics of the participants with missing values was compared to that of the participants who were included in the analysis. The results showed that there was no significant difference in the age distribution (median age [IQR], 46 [37–56] versus 48 [32–57], P = 0.697) or neurosyphilis prevalence (65.5% versus 56.6%, P = 0.239) between participants with missing values and those included in the analysis. However, the sex ratio of the participants with missing values was significantly different from that of the included patients (male: female, 43:15 versus 86:66, P = 0.019). Therefore, further stratified analysis was carried out according to sex and age. After stratification by sex and age, there was still no significant difference in the positive rate between the two tests in each subgroup (P > 0.05), and the kappa value between the two tests varied from 0.926 to 1.0 in each subgroup (P for κ < 0.001).
There was no significant difference in the positive rate between the CSF-TRUST-17 test and the CSF-VDRL test (40.5% [85/210] versus 42.4% [89/210], P = 0.125). The positive and negative predictive values of the CSF-TRUST-17 test were 100.0% and 96.8%, respectively. The agreement rate between the two tests was 98.1% (206/210), and the Kappa value was 0.961 (P for κ < 0.001), indicating that the strength of agreement was almost perfect. After stratifying by sex and age, there was still no significant difference in the positive rate between the two tests in each subgroup (P > 0.05), and the kappa value between the two tests varied from 0.939 to 0.969 in each subgroup (P for κ < 0.001) (Table 3).
Table 3.
Concordance between the qualitative CSF-TRUST-10 and CSF-TRUST-17 tests and the CSF-VDRL.
| CSF-VDRL | P for χ2 | Positive predictive value | Negative predictive value | Agreement | κ | P for κ | ||
|---|---|---|---|---|---|---|---|---|
| Positive | Negative | |||||||
| CSF-TRUST-10 | ||||||||
| The whole cohort (n = 152)a | 0.500 | 100.0% | 97.9% | 98.7% | 0.972 | <0.001 | ||
| Positive | 57 | 0 | ||||||
| Negative | 2 | 93 | ||||||
| Subgroups by sex | ||||||||
| Male (n = 86) | >0.999 | 100.0% | 100.0% | 100.0% | 1.0 | <0.001 | ||
| Positive | 39 | 0 | ||||||
| Negative | 0 | 47 | ||||||
| Female (n = 66) | 0.500 | 100.0% | 95.8% | 97.0% | 0.926 | <0.001 | ||
| Positive | 18 | 0 | ||||||
| Negative | 2 | 46 | ||||||
| Subgroups by age | ||||||||
| <60 (n = 127) | 0.500 | 100.0% | 97.6% | 98.4% | 0.965 | <0.001 | ||
| Positive | 43 | 0 | ||||||
| Negative | 2 | 82 | ||||||
| ≥60 (n = 25) | >0.999 | 100.0% | 100.0% | 100.0% | 1.0 | <0.001 | ||
| Positive | 14 | 0 | ||||||
| Negative | 0 | 11 | ||||||
| CSF-TRUST-17 | ||||||||
| The whole cohort (n = 210) | 0.125 | 100.0% | 96.8% | 98.1% | 0.961 | <0.001 | ||
| Positive | 85 | 0 | ||||||
| Negative | 4 | 121 | ||||||
| Subgroups by sex | ||||||||
| Male (n = 129) | 0.500 | 100.0% | 97.0% | 98.4% | 0.969 | <0.001 | ||
| Positive | 63 | 0 | ||||||
| Negative | 2 | 64 | ||||||
| Female (n = 81) | 0.500 | 100.0% | 96.6% | 97.5% | 0.939 | <0.001 | ||
| Positive | 22 | 0 | ||||||
| Negative | 2 | 57 | ||||||
| Subgroups by age | ||||||||
| <60 (n = 176) | 0.250 | 100.0% | 97.3% | 98.3% | 0.964 | <0.001 | ||
| Positive | 65 | 0 | ||||||
| Negative | 3 | 108 | ||||||
| ≥60 (n = 34) | >0.999 | 100.0% | 92.9% | 97.1% | 0.939 | <0.001 | ||
| Positive | 20 | 0 | ||||||
| Negative | 1 | 13 | ||||||
Abbreviations: CSF, cerebrospinal fluid; VDRL, venereal disease research laboratory; TRUST, toluidine red unheated serum test.
The results of the CSF-TRUST-10 test were missing for 58 participants.
3.4. The concordance between the quantitative CSF-VDRL and the CSF-TRUST-10 and CSF-TRUST-17 tests
Compared with the quantitative CSF-VDRL test, 91.4% (139/152) of the quantitative CSF-TRUST-10 results were in complete agreement with the results of that test. For the patients having the same qualitative CSF-TRUST-10 results as the CSF-VDRL test, 6.7% (10/150) of them had one-titre lower quantitative CSF-TRUST-10 results than the CSF-VDRL test, and 0.7% (1/150) of them had one-titre higher quantitative CSF-TRUST-10 results than the CSF-VDRL test. For the remaining two patients with discordant qualitative CSF-TRUST-10 results with the CSF-VDRL test, the quantitative CSF-VDRL results were all 1:1. There was no significant difference in the proportional distribution between the results of the two quantitative tests (P > 0.05). The weighted Kappa value between the two quantitative tests was 0.939 (P for κ < 0.001), indicating that the strength of agreement was almost perfect (Table 4).
Table 4.
Concordance between the quantitative CSF-TRUST-10 and CSF-TRUST-17 tests and the CSF-VDRL test.
| CSF-VDRL | P for χ2 | Agreement | Weighted κ | P for weighted κ | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Negative | 1:1 | 1:2 | 1:4 | 1:8 | 1:16 | 1:32 | 1:64 | 1:128 | |||||
| CSF-TRUST-10a | 0.066 | 91.4% | 0.939 | <0.001 | |||||||||
| Negative | 93 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ||||
| 1:1 | 0 | 16 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | ||||
| 1:2 | 0 | 0 | 12 | 2 | 0 | 0 | 0 | 0 | 0 | ||||
| 1:4 | 0 | 0 | 1 | 8 | 5 | 0 | 0 | 0 | 0 | ||||
| 1:8 | 0 | 0 | 0 | 0 | 6 | 1 | 0 | 0 | 0 | ||||
| 1:16 | 0 | 0 | 0 | 0 | 0 | 2 | 0 | 0 | 0 | ||||
| 1:32 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | ||||
| 1:64 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ||||
| 1:128 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | ||||
| CSF-TRUST-17 | 0.007 | 87.6% | 0.919 | <0.001 | |||||||||
| Negative | 121 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ||||
| 1:1 | 0 | 20 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | ||||
| 1:2 | 0 | 2 | 17 | 2 | 0 | 0 | 0 | 0 | 0 | ||||
| 1:4 | 0 | 0 | 3 | 11 | 9 | 0 | 0 | 0 | 0 | ||||
| 1:8 | 0 | 0 | 0 | 0 | 8 | 0 | 0 | 0 | 0 | ||||
| 1:16 | 0 | 0 | 0 | 0 | 0 | 5 | 2 | 0 | 0 | ||||
| 1:32 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | ||||
| 1:64 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ||||
| 1:128 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | ||||
Abbreviation: CSF, cerebrospinal fluid; VDRL, venereal disease research laboratory; TRUST, toluidine red unheated serum test.
The results of the CSF-TRUST-10 test were missing for 58 participants.
Compared with the quantitative CSF-VDRL test, 87.6% (184/210) of the quantitative CSF-TRUST-17 results were in complete agreement. For the patients having the same qualitative CSF-TRUST-17 results as the CSF-VDRL test, 8.3% (17/206) of them had one-titre lower quantitative CSF-TRUST-17 results than the CSF-VDRL test; 2.4% (5/206) of them had one-titre higher quantitative CSF-TRUST-17 results than the CSF-VDRL test. For the remaining four patients with discordant qualitative CSF-TRUST-17 results with the CSF-VDRL test, the quantitative CSF-VDRL results were all 1:1. The proportional distribution of the quantitative CSF-TRUST-17 results was significantly different from that of the quantitative CSF-VDRL test (P = 0.007). The weighted Kappa value between the two quantitative tests was 0.919 (P for κ < 0.001), indicating that the strength of agreement was almost perfect (Table 4).
4. Discussion
During a syphilis infection, an antibody-like substance called reagin, which is formed by the host in response to lipids released from damaged host cells early in infection with T. pallidum and lipid-like material from the treponemal cell surface, can be detected in the patient's serum [17]. In syphilis infection of the central nervous system, reagin can be detected in the CSF. The CSF-VDRL test remains the only recommended test for the laboratory diagnosis of neurosyphilis until now [3]. However, the situation is even more challenging in China, as there is no commercial VDRL reagent approved by the National Medical Products Administration for CSF-VDRL examination [8]. Thus, this study determined the optimum amount of antigen of the CSF TRUST in replacement of the CSF VDRL test for neurosyphilis diagnosis. In our results, there was no significant difference in the diagnostic performance for neurosyphilis between the CSF-TRUST-10 tests and CSF-VDRL tests or with either positive rate. The agreement rates between the two tests were as high as 98.7%. The 1.3% discordant results only occurred in the condition of very low CSF-VDRL titres (≤1:1). For quantitation, the consistency between the CSF-VDRL and CSF-TRUST-10 tests was outstanding, of which the agreement rate was 91.4% and the weighted Kappa value was 0.939 (P for κ < 0.001), and the discordant results were no more than two titres, indicating that the strength of agreement between the two tests was almost perfect.
Similarly, the diagnostic performance of the CSF-TRUST-17 test for neurosyphilis was comparable to that of the CSF-VDRL test, as was the positive rate. However, a larger amount of TRUST antigen did not bring a better diagnostic performance. The results of the quantitative CSF-TRUST-17 test fluctuated more, of which 2.4% were higher and 10.0% were lower than those of the CSF-VDRL test, resulting in a proportional distribution that was significantly different from that of the quantitative CSF-VDRL test.
As a modification based on the VDRL test, the TRUST used sized toluidine red particles added to the antigen as markers. Thus, the presence of flocculation of the antigen-antibody complex on the slides could be read macroscopically immediately after rotation [4]. Additionally, the TRUST antigen is added with choline chloride and ethylene diamine tetraacetic acid to enhance the reactivity of the test and stabilized the antigen suspension. The TRUST could be performed at room temperature (23–29 °C), and the TRUST reagents are stored at 2–8 °C. Compared to the VDRL test, the TRUST is easy to operate and is accessible in China, and there are multiple commercial TRUST reagents approved by the National Medical Products Administration for use in serum testing in the laboratory diagnosis of syphilis. A nationwide survey that included hospitals located in 116 cities in China demonstrated that of 154 hospitals that were capable of performing serological tests on CSF for syphilis, only 11.0% (17/154) of the hospitals could perform CSF VDRL tests, whereas most laboratories could only perform the CSF TRUST [8]. Our results indicated high consistency of the results between the CSF-TRUST and CSF VDRL tests, which provided strong evidence for the application of the CSF-TRUST in the diagnosis of neurosyphilis.
To the best of our knowledge, this is the first study to determine the optimum amount of antigen of the CSF TRUST in replacement of the CSF VDRL test for neurosyphilis diagnosis. However, this study has several limitations that need to be addressed. First, the included participants were suspected of having a diagnosis of neurosyphilis and had an indication for lumbar puncture and CSF examination for syphilis, but they were not selected randomly, raising the concern of selection bias. Additionally, for this reason, the prevalence of neurosyphilis, as well as the positive rate of the CSF-VDRL test, might be higher in the present study than in similar studies. Second, to be noted, although the sensitivity of the CSF-TRUST-10 test was very close to that of the CSF-VDRL, a rare missed diagnosis would still be unfortunate. Thus, a diagnosis or exclusion of neurosyphilis should be based on not only the result of CSF-TRUST-10 test but also a combination of clinical manifestations and other CSF parameters. Additionally, the sensitivity of TRUST in CSF still needs to be improved.
In conclusion, our study demonstrated that the CSF-TRUST using 10 μL or 17 μL of antigen had comparable diagnostic performance with the CSF-VDRL test for neurosyphilis. The CSF-TRUST with 10 μL of antigen was highly recommended as the optimal alternative for the CSF-VDRL test; the qualitative results of the CSF-TRUST could completely replace those of the CSF-VDRL test in clinical practice. Our results provide a basis for using TRUST to guide neurosyphilis diagnosis.
Author contribution statement
Yao Xiao: Analyzed and interpreted the data; Wrote the paper.
Man-Li Tong: Performed the experiments.
Yang Yang: Contributed reagents, materials, analysis tools or data.
Wei-Ming Gu; Li-Li Liu; Tian-Ci Yang: Conceived and designed the experiments.
Funding statement
This work was supported by the National Natural Science Foundation of China [grant numbers 82003512, 81973104, 82272370, 81971147, 82271387] and the Natural Science Foundation of Fujian Province, China [grant number 2021J02055].
Data availability statement
Data will be made available on request.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Contributor Information
Wei-Ming Gu, Email: weiminggu_sh@126.com.
Li-Li Liu, Email: liulili@xmu.edu.cn.
Tian-Ci Yang, Email: yangtianci@xmu.edu.cn.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Data will be made available on request.