1. Optimization of antibody working concentration
The checkerboard experiment was performed with biotin-labeled antibody and HRP-labeled antibody, and different antibody concentrations were selected for detection to determine the RLU of 6 standards, and the results are shown in supplementary table 1. When the Biotin-Ab concentration is 2.6 µg/mL and the HRP-Ab concentration is 0.24 µg/mL, the signal value of each calibrator is suitable and the ratio is close, and the lower antibody concentration is selected under the same conditions to reduce the cost, and the combination was selected as the working concentration of the antibody in this study.
2. Optimal incubation time
The duration of the incubation period impacts RLU levels, and various time intervals were assessed to evaluate calibrators 1–5, plasma samples of high and low values. The outcomes are displayed in Fig. 1. An incubation period of 10 minutes yielded higher signal values across the board. Significantly reducing the testing time and improving detection throughput can be achieved by selecting a shorter incubation period. Consequently, this kit's reaction conditions were established at 37°C for 10 minutes.
3. Evaluation of methodological performance
The method performance was evaluated according to the EP guidelines of the Clinical and Laboratory Standards Institute (CLSI).
3.1 Limit of detection
As demonstrated in Table 1, we calculated the mean and standard deviation of RLU for 20 standard dilutions. We then integrated M + 2SD into the standard curve, resulting in concentration values of 1.104 ng/mL, 1.153 ng/mL, and 1.160 ng/mL. Consequently, we confirmed that the lowest detection limit for this method is 1.2 ng/mL.
Table 1
Verification results of the limit of detection
Indicators | Test1 | Test2 | Test3 |
M | 39792 | 40308 | 40653 |
SD | 2017 | 2244 | 2132 |
M + 2SD | 43825 | 44797 | 44916 |
LOD (ng/mL) | 1.104 | 1.153 | 1.160 |
Abbreviation: M, Mean; SD, Standard deviation; LOD, Limit of detection. |
3.2 Linearity
The high concentration samples were diluted using a gradient of low concentration samples to conduct the linearity test, as depicted in figure 2. The results demonstrate a strong, linear relationship between the theoretical and actual concentrations of the samples, as evidenced by the good linear regression equation obtained from fitting the data in figure 2: Y = 0.9433x + 0.6914, R>0.99.
3.3 Accuracy
As shown in supplementary table 2, the deviations of theoretical and measured concentrations were 4.62% and 0.98%, respectively, within ±10%.
3.4 Precision
Precision tests were conducted for both the low and high value quality controls (QCs), with supplementary table 3 documenting the results. The intra-batch coefficient of variation (CV) for the low-value QCs was 6.68%, 6.25%, and 5.66%, with an inter-batch CV of 6.74%. The high-value QCs had an intra-batch CV of 5.77%, 6.73%, and 5.64%, with an inter-batch CV of 6.03%. All the results were less than 10%.
3.5 Acceleration Stability
The experimental results showed that the deviation of the concentration of the QCs was less than 10% when the kit was placed at 37°C for different times compared to storage at 4°C (Table 2), indicating that the method demonstrates good stability.
Table 2 Verification results of thermal stability
Time
|
Samples
|
Labeled Concentrations
|
Measured Concentration
|
Bias
|
test1
|
test2
|
test3
|
test1
|
test2
|
test3
|
1 Day
|
Sample 1
|
4.83
|
4.79
|
5.07
|
4.51
|
-0.83%
|
4.97%
|
-6.63%
|
Sample 2
|
16.62
|
17.17
|
16.92
|
17.52
|
3.31%
|
1.81%
|
5.42%
|
3 Day
|
Sample 1
|
4.83
|
5.12
|
4.87
|
4.67
|
6.00%
|
0.83%
|
-3.31%
|
Sample 2
|
16.62
|
17.50
|
17.11
|
17.08
|
5.29%
|
2.95%
|
2.77%
|
6 Day
|
Sample 1
|
4.83
|
4.79
|
4.62
|
5.04
|
-0.83%
|
-4.35%
|
4.35%
|
Sample 2
|
16.62
|
16.80
|
17.28
|
15.97
|
1.08%
|
3.97%
|
-3.91%
|
10 Day
|
Sample 1
|
4.83
|
4.58
|
5.02
|
4.63
|
-5.18%
|
3.93%
|
-4.14%
|
Sample 2
|
16.62
|
15.30
|
17.01
|
15.30
|
-7.94%
|
2.35%
|
-7.94%
|
3.6 Clinical evaluation
120 copies of clinical plasma were tested by this method with the Japanese Sysmex kit. The correlation coefficient R was 0.979 was calculated after analysis, and there was good agreement between the two assays (Figure 3).
4. Comparison of t-PAIC, TAT, PIC, TM, D-D and FDP between Control group and gastric cancer groups
As shown in table 3, we found that TAT, TM, PIC, D-D, and FDP were significantly higher than those of the control group, and the differences were statistically significant (P < 0.001 or P < 0.05). t-PAIC did not show significant differences (P > 0.05).
Table 3 Comparison of each test index between gastric cancer population and healthy population
Groups
|
Control Group
|
GC Group
|
Z Value
|
P Value
|
N
|
80
|
293
|
t-PAIC (ng/mL)
|
4.43 (2.96,6.60)
|
4.49 (3.00,6.89)
|
-0.288
|
0.773
|
TM (TU/mL)
|
6.75 (5.21,8.44)
|
7.84 (5.73,11.61)
|
-3.564
|
<0.001
|
TAT (ng/mL)
|
2.60 (2.13,3.71)
|
8.91 (5.75,12.89)
|
-12.171
|
<0.001
|
PIC (μg/mL)
|
0.32 (0.20,0.50)
|
0.68 (0.47,0.94)
|
-9.188
|
<0.001
|
D-D (mg/L)
|
0.36 (0.25,0.46)
|
0.85 (0.40,2.26)
|
-7.952
|
<0.001
|
FDP (mg/L)
|
3.35 (2.35,4.30)
|
3.40 (2.10,7.20)
|
-2.017
|
0.044
|
Abbreviation: GC: Gastric cancer; t-PAIC: Tissue plasminogen activator inhibitor complex; TAT: Thrombin-antithrombin complex; TM: Thrombomodulin; PIC: plasmin-α2-plamininhibitor complex; D-D: D-Dimer; FDP: Fibrinogen degradation product. * P < 0.05 considered statistically significant.
5. Comparison of t-PAIC, TAT, PIC, TM, D-D, and FDP in the thrombus and non-thrombus groups of gastric cancer patients
As shown in table 4, t-PAIC, TAT, PIC, TM, D-D, and FDP were significantly higher in the thrombus group than in the non-thrombus group, and the differences were statistically significant (P < 0.001 or P < 0.05).
Table 4 Comparison of each test index in thrombosis group and non-thrombosis group of gastric cancer patients
Groups
|
Non-thrombosis group
|
Thrombosis group
|
Z Value
|
P Value
|
N
|
239
|
54
|
t-PAIC (ng/mL)
|
4.43 (2.96,6.33)
|
5.24 (3.04,17.27)
|
-0.247
|
0.014
|
TM (TU/mL)
|
7.48 (5.62,10.74)
|
10.88 (6.85,13.87)
|
-3.505
|
<0.001
|
TAT (ng/mL)
|
7.67 (5.34,10.96)
|
16.99 (11.63,26.61)
|
-8.469
|
<0.001
|
PIC (μg/mL)
|
0.66 (0.45,0.90)
|
0.88 (0.53,1.48)
|
-3.113
|
0.002
|
D-D (mg/L)
|
0.75 (0.36,1.85)
|
1.78 (0.78,5.05)
|
-3.816
|
<0.001
|
FDP (mg/L)
|
3.20 (2.10,5.80)
|
6.15 (2.70,16.55)
|
-3.721
|
<0.001
|
Abbreviation: GC: Gastric cancer; t-PAIC: Tissue plasminogen activator inhibitor complex; TAT: Thrombin-antithrombin complex; TM: Thrombomodulin; PIC: plasmin-α2-plamininhibitor complex; D-D: D-Dimer; FDP: Fibrinogen degradation product. * P < 0.05 considered statistically significant.
6. Comparison of t-PAIC, TAT, PIC, TM, D-D, and FDP in gastric cancer stages I-II and III-IV
According to table 5, t-PAIC, TAT, PIC, TM, D-D and FDP were significantly higher in stages III-IV than in stages I-II, and the difference was statistically significant (P < 0.001 or P < 0.05).
Table 5 Comparison of each test index in stages I-II and III-IV
Groups
|
Stage Ⅰ-Ⅱ
|
Stage Ⅲ-Ⅳ
|
Z Value
|
P Value
|
N
|
112
|
181
|
t-PAIC (ng/mL)
|
4.02 (2.81,5.72)
|
4.78 (3.20,7.40)
|
-2.603
|
0.009
|
TM (TU/mL)
|
7.26 (5.13,10.88)
|
8.26 (6.08,12.02)
|
-2.324
|
0.02
|
TAT (ng/mL)
|
6.69 (3.75,9.15)
|
10.36 (6.90,15.34)
|
-6.455
|
<0.001
|
PIC (μg/mL)
|
0.52 (0.37,0.68)
|
0.86 (0.60,1.08)
|
-7.502
|
<0.001
|
D-D (mg/L)
|
0.38 (0.22,0.69)
|
1.59 (0.75,3.36)
|
-9.874
|
<0.001
|
FDP (mg/L)
|
2.20 (1.70,3.20)
|
5.40 (3.00,11.00)
|
-9.164
|
<0.001
|
Abbreviation: GC: Gastric cancer; t-PAIC: Tissue plasminogen activator inhibitor complex; TAT: Thrombin-antithrombin complex; TM: Thrombomodulin; PIC: plasmin-α2-plamininhibitor complex; D-D: D-Dimer; FDP: Fibrinogen degradation product. * P < 0.05 considered statistically significant.
7. Evaluation of the value of each marker in the diagnosis of VTE by re-ceiver operating characteristic (ROC) curve
For the diagnosis of VTE, the area under the curve (AUC) of t-PAIC, TM, TAT, PIC, D-D, and FDP were 0.608, 0.653, 0.869, 0.636, 0.666, and 0.662, respectively. t-PAIC, TM, TAT, PIC, D-D, and FDP had critical values of 9.96 ng/ mL, 9.54 TU/mL, 9.61 ng/mL, 0.82 μg/mL, 1.40 mg/L, and 5.85 mg/L, respectively. TAT had a good diagnostic value for VTE, with a sensitivity of 90.7% and a specificity of 69%. t-PAIC had an AUC of 0.608, and it had the lowest diagnostic efficiency (Supplementary Table 4, Figure 4). When the six markers were applied in combination, the AUC of "t-PAIC+TM+TAT+PIC" and "t-PAIC+TM+TAT+PIC+D-D+FDP" were significantly higher than that of "D-D+FDP" for VTE in gastric cancer patients. "The AUC, sensitivity and specificity of "D-D+FDP" were 0.66, 55.6% and 76.2%, respectively, while the AUC of "t-PAIC+TM+TAT+PIC" was 0.66, 55.6% and 76.2%, respectively. +PIC" had an AUC, sensitivity and specificity of 0.90, 85.2% and 82.8%, respectively. The AUC, sensitivity and specificity of "t-PAIC+TM+TAT+PIC+D-D+FDP" were 0.904, 81.5% and 86.6%, respectively (Supplementary Table 5, Figure 4).