Clinical analysis of blood markers and imaging for diagnosis and prognosis of rheumatoid arthritis


 Background The purpose of this study is to explore the combined diagnostic value of anti-cyclic citrullinated peptide antibody (A-CCP), rheumatoid factor (RF) and imaging result in early rheumatoid arthritis, and the role of A-CCP and RF in prediction for radiological outcomes. Methods 101 patients with rheumatoid arthritis and 97 control individuals were detect their A-CCP, RF and radiological joint changes, the diagnostic efficacy of the respective indicators and the combined indicators was analyzed by logistic regression model. Results Our results showed that values of A-CCP and RF were significantly higher in the RA group than in the normal group. Receiver operating characteristic curve results show that the sensitivity of RF is higher than A-CCP and radiological outcome, and specificity of CCP is higher than RA and radiological outcome, and the diagnostic ability of combination of RF, A-CCP and radiological outcome is the strongest. Furthermore, RF and A-CCP had high significant OR for radiological joint damage and progression. Conclusions Our study indicated that the combined diagnosis of RF and A-CCP with radiological outcome can improve the diagnostic efficacy of RA, and RF and A-CCP are independent predictors of radiological damage and progression.


Background
The purpose of this study is to explore the combined diagnostic value of anti-cyclic citrullinated peptide antibody (A-CCP), rheumatoid factor (RF) and imaging result in early rheumatoid arthritis, and the role of A-CCP and RF in prediction for radiological outcomes.
Methods 101 patients with rheumatoid arthritis and 97 control individuals were detect their A-CCP, RF and radiological joint changes, the diagnostic efficacy of the respective indicators and the combined indicators was analyzed by logistic regression model.

Results
Our results showed that values of A-CCP and RF were significantly higher in the RA group than in the normal group. Receiver operating characteristic curve results show that the sensitivity of RF is higher than A-CCP and radiological outcome, and specificity of CCP is higher than RA and radiological outcome, and the diagnostic ability of combination of RF, A-CCP and radiological outcome is the strongest. Furthermore, RF and A-CCP had high significant OR for radiological joint damage and progression.

Conclusions
Our study indicated that the combined diagnosis of RF and A-CCP with radiological outcome can improve the diagnostic efficacy of RA, and RF and A-CCP are independent predictors of radiological damage and progression.

Background
Rheumatoid arthritis is a clinically common autoimmune disease (1). The main clinical feature of patients is synovitis. Patients usually gradually affect the large joints from the symptoms of small joints. Those with severe conditions may even have stiff and deformed conditions that affect the patient's Quality of life and physical and mental health. At this stage, the best way to prevent rheumatoid arthritis is early detection and treatment, but because most patients do not have typical symptoms early in the disease, and the clinical symptoms are complex and diverse, it is difficult to accurately judge by clinical symptoms. At present, the most commonly used examination methods are rheumatoid factor (RF) detection and imaging examination, but RA patients detected by imaging have bone and joint lesions, and RF in serological examination lacks specificity (2)(3)(4)(5), which is not conducive to early diagnosis And treatment, so the diagnosis of early RA through serological indicators is particularly important.
A-CCP antibodies are IgG-based antibodies, which are specific indicators for the early diagnosis of rheumatoid arthritis (6). A-CCP antibodies are secreted spontaneously by B lymphocytes in patients with rheumatoid arthritis, while B lymphocytes are not secreted spontaneously in normal or other disease groups. Previous studies have shown that A-CCP antibodies can appear early in the onset of RA patients, so this antibody can be used to screen for early RA (5). A-CCP antibodies are highly specific in the diagnosis of RA and can be insufficiently complementary to RF.
This study aims to combine the detection of early changes in serum markers CCP, RF and imaging result in patients with rheumatoid arthritis, and use the logistic regression model to combine serum markers and imaging result to form different diagnostic combinations to study the best diagnosis mode of early RA. Our result shows that, in terms of the diagnostic efficacy of RA, A-CCP is more specific than RF and imaging result, while RF is more sensitive than CCP and imaging result. Combining RF, CCP and imaging result has the highest diagnostic efficacy. Our results show that combined diagnosis of RF and A-CCP with radiological outcome can improve the diagnostic efficacy of RA, and RF and A-CCP are independent predictors of radiological damage and progression.

Case collection
A total of 148 patients with suspected rheumatoid arthritis were included in the study. Among them, 101 patients diagnosed with rheumatoid arthritis were classified in the RA group, other 47 patients who were not diagnosed as RA in the initial diagnosis were divided into non-RA patients group as control group together with 50 healthy persons. All individuals were diagnosed by joint testing, including A-CCP, RF and imaging testing.
In the rheumatoid arthritis group, there were 35 males and 66 females, aged 22 to 75 years, with an average of (52.46 ± 6.17) years, the disease duration was 0.5 to 2 years, with an average of (1.46 ± 0.23) years. In the nonrheumatoid arthritis group, there were 50 males and 47 females, aged 20-76 years, with an average age of (53.22 ± 5.44) years. Inclusion criteria: (1) Patients in the rheumatoid arthritis group all met the diagnostic criteria for rheumatoid arthritis(7). (2) participants agreed to the study with informed consent. Exclusion criteria: (1) Individuals who disagree with this researcher. (2) Patients with a course of more than 2 years. This study has been approved by the Third people's and Haici Hospital Medical Ethics Committee and all participants are informed and agree.

Detection method
Venous blood was collected from all subjects in the morning on an empty stomach. RF was detected by immunoturbidimetry (Roche, Cobas8000, Germany), and CCP (Zhonghan Shengtai Biotechnology Co., Ltd., China) was detected by latex immunoturbidimetry.

Radiographic measurement
According to the imaging examination results, the disease can be divided into four stages. Stage Ⅰ is the early stage, stage Ⅱ is the middle stage(8).
Statistical method Stata 12.0 statistical software was used to analyze the data. The measurement data was expressed as mean ± standard deviation (x ± s), using t test, and p < 0.05 was considered statistically significant. Diagnosis ability and Odds ratios (OR) was evaluated using logistic regression model, ROC curve was used to analyze the ability of individual diagnosis and joint diagnosis.

CCP and RF concentration in blood was significantly increased in patients with RA
In order to verify whether RF and A-CCP were significantly increased in patients with RA, we measured the RF and A-CCP concentrations in the blood of 101 patients with RA and 97 controls. As shown in Table 1, in RA patient group, the average RF concentration and the range were 97 (2-278) IU/ml, the average A-CCP concentration and the range were 62 (2-235) RU/ml. The average RF concentration and the range of control people were 22 (2-83) IU/ml, the average A-CCP concentration and the range were 12 (2-32) RU/ml. The results showed that the mean values of RF and A-CCP in the RA group were significantly higher than values in the control group, and the mean values between two groups were statistically significant. The RF and A-CCP concentration in blood was significantly increased in patients with RA.
The results showed that the median values of RF and A-CCP in the RA group were significantly higher than values in non-RA group, and the median values were statistically significant. *p < 0.05 indicates statistical significance.

Establish logistic regression model to evaluate the diagnostic efficacy of RF, A-CCP and imaging for RA
We constructed a diagnostic model to compare diagnostic ability of RF, A-CCP and imaging for RA. As showed in Fig. 1, the area under the curve (AUC) was established to evaluate the diagnostic ability of RF, A-CCP and imaging, and their combined diagnostic ability. Table 2 summarized the AUC, sensitivity, specificity, positive predictive and negative predictive value of RF, A-CCP and imaging. The value of RF was 0.89, 80%, 82%, 83%, 80%, respectively. The value of A-CCP was 0.88, 72%, 93%, 91%, 76%, respectively, while the value of imaging outcome was 0.79, 76%, 82%, 77%, 76%. We also evaluated their combined diagnostic ability, the result of RF + A-CCP was 0.96, 88%, 92%, 92%, 88%, the result of RF + A-CCP + radiological outcome was 0.98, 90%, 93%, 93%, 90%, respectively. Figure 1 and Table 2 results showed that The AUC value of RF is higher than that of A-CCP and radiological outcome. RF sensitivity is higher than A-CCP and radiological outcome, but specificity of RF and radiological outcome is lower than A-CCP. The positive predictive value of RF and radiological outcome is lower than A-CCP, while the negative predictive value is higher than A-CCP and radiological outcome. Combined RF, A-CCP with and radiological outcome had best AUC, sensitivity, specificity, positive predictive value and negative predictive value. Results of the diagnostic efficacy of A-CCP is the same as RF, and the sensitivity and specificity are complementary to RF indicate that A-CCP has good diagnostic efficacy for RA and is an effective supplement to RF diagnosis of RA. Although that diagnostic efficacy of radiological outcome is weaker than RF and A-CCP, but the combined diagnosis of RF and A-CCP with radiological outcome is an effective mode for the diagnosis of RA. Summarized the AUC, sensitivity, specificity, positive predictive value and negative predictive value of RF, A-CCP and radiological outcome for the diagnosis of RA.

High levels of RF and A-CCP are associated with an increased risk of RA
logistic regression was used to estimate the cutoff value, odds ratios (ORs) and 95% confidence intervals (CIs).
Our results show that according to the Youden index, the cutoff value for RF that can distinguish RA patients from non-RA patients was 38 IU/ml, while the cutoff value for A-CCP was 32 RU/ml. The results in Table 3 show that in the early and middle stages of RA, according to the cutoff value, a significant increased RA risk was found for individuals with RF concentrations ≥ 38 IU/ml compared to RF < 38 IU/ml (11.49  The prediction effect of RF on the early stage of RA is significantly stronger than middle stage of RA. The prediction effect of A-CCP on the early stage of RA is slightly stronger than that on the middle stage of RA. Categorical cut-points determined using the Youden Index. Imaging staging according to criteria of Rheumatoid arthritis classification (2010). OR: odds ratio, CI: confidence interval.

Discussion
The purpose of this study is to evaluate the role of RF, A-CCP and imaging in the diagnosis of early RA. RA is a systemic disease, mainly involving peripheral joints. If early treatment can reduce the disability rate, treatment within 3 to 6 months after the disease is the best treatment time for RA patients, so early diagnosis and treatment of RA patients can improve the patient's Quality of life (5,7). This study found that both RF and A-CCP antibodies have good diagnostic efficacy for early RA. The sensitivity and specificity of the two can complement each other. Our results indicate that hematological indicators combined with imaging results can significantly improve the diagnostic efficacy of early RA The results of our study found that the serum A-CCP antibody and RF levels in the early RA group were significantly higher than the control group, and the differences were statistically significant (p < 0.05). Our research results confirmed that in the process of early RA, RF and A-CCP antibody serum levels increased, RF and A-CCP antibodies are serological markers for the diagnosis of early RA. RF is located in the Fc segment of anti-human or animal IgG and is widely present in the blood and joint fluid of RA patients (9). The results of multiple studies have shown that RF has relatively high sensitivity in the early diagnosis, but its specificity is not high, and it has a certain positive rate in systemic lupus erythematosus and chronic active hepatitis, even positive persons may be present in healthy people. This study found that RF has a higher sensitivity (82%) in the diagnosis of RA, a relatively low specificity (80%), a positive predictive value of 83%, and a negative predictive value of 80%. RF is conducive to screening but not to diagnosis, and other indicators should be combined to reduce the rate of misdiagnosis.
The peptide fragments of the cyclic filament protein are A-CCP antibodies, which are mostly of IgG type (10,11). Schellekens et al. Synthesized CCP antigen peptides. This antigen can be used to detect A-CCP antibodies in patients (12). A-CCP antibodies can appear early in the onset of RA patients, so this antibody can be used to screen early RA. The A-CCP antibody has a high specificity in the diagnosis of rheumatoid arthritis. It can be used not only for the early diagnosis of rheumatoid arthritis, but also for judging whether arthritis is invasive and providing effective guidance for clinical treatment. However, the sensitivity of A-CCP antibodies is low, and simple detection has obvious limitations. In this study, we found that the sensitivity of A-CCP antibodies was 72%, specificity was 93%, positive predictive value was 91%, and negative predictive value was 76%. Our results indicate that A-CCP antibodies can be used as complementary serological markers to improve the sensitivity and specificity of RA diagnosis.
Logistic regression model results show that the AUC of RF and A-CCP antibody combined diagnosis of RA is 0.96, which is higher than the respective AUC of RF (0.89) and A-CCP antibody (0.88). The sensitivity of the combined diagnosis is 88%, which is also higher than the respective sensitivity of RF (80%) and A-CCP antibody (72%). The specificity of the combined diagnosis was 92%, which was higher than the RF specificity (82%) and lower than the A-CCP antibody specificity (93%). The positive predictive value is 92%, and the negative predictive value is 88%. It can be seen that this combination can significantly improve the performance of diagnosing RA. The results of this study are consistent with previous studies (13)(14)(15).
The diagnosis of RA mainly depends on clinical manifestations, laboratory examination and imaging examination. Typical cases are not difficult to diagnose, but early patients and atypical cases are easy to be missed or misdiagnosed (16,17). These patients who are easily misdiagnosed or missed should be combined with laboratory and imaging results (18)(19)(20), our result that combined diagnosis of RF, A-CCP and radiological outcome has the highest diagnostic ability for RA conforms that combined blood and imaging is an effective mode for the diagnosis of RA. However, laboratory results have not been reported to predict the imaging increased risk of RA in people with different imaging stages. This study is the first to predict the risk of RA in people with different imaging stages in laboratory results. The results ( Table. 3) found that the prediction effect of RF on the early stage of RA is significantly stronger than the middle stage of RA. The prediction effect of A-CCP on the early stage of RA is slightly stronger than that on the middle stage of RA. Especially in the early stage of imaging invasion, the OR value of RF (11.49) is the highest, indicating that with the increase of RF, the imaging increased risk of RA is greater. This results are consistent with previous study (21).
A-CCP antibodies and RF are commonly used indicators for the diagnosis of rheumatoid arthritis, and each has its own advantages, but any one test has its own limitations (5,14,22,23). Less sensitive in the diagnosis of rheumatoid arthritis and can increase the risk of missed diagnosis. The low specificity can increase the risk of misdiagnosis. The combined testing of various indicators can make up for the deficiencies of single index testing to a great extent, reduce the risk of missed diagnosis and misdiagnosis, and facilitate the early diagnosis of the diagnosis, so that patients can receive symptomatic treatment in a timely manner to maximize the prognosis of patients (24).

Conclusions
The combined detection of A-CCP and RF with imaging has a high diagnostic efficiency in the diagnosis of rheumatoid arthritis, which can provide reliable reference information for clear clinical diagnosis.