Objective  To explore the concentration and integrity of circulating free DNA (cfDNA) in plasma, and its diagnostic value for benign and malignant pulmonary nodules.

Methods  According to pathological diagnosis results, the patients were divided into benign pulmonary nodules group(60 cases) and malignant pulmonary nodule group(50 cases), and another 30 healthy examiners in the same period were selected as control group. Plasma carcinoembryonic antigen (CEA) and cytokeratin fragment 19 (Cyfra21-1) expression levels were detected by enzyme-related immunosorbent assay (ELISA). The cfDNA level and cfDNA integrity were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Receiver operating characteristic (ROC) curve was drawn, and the diagnostic value of cfDNA, CEA and Cyfra21-1 in NSCLC was analyzed by ROC curve, and the diagnostic efficacy of each index and their combination was compared.

Results  Compared with the benign pulmonary nodule group 385.43 (176.45, 704.55), 0.37 (0.26, 0.59) ng/mL, 2.67 (1.36, 5.45) ng/mL, 2.74 (1.43, 3.96) ng/mL, the plasma levels of cfDNA 1 154.83 (452.85, 1 642.31) ng/mL, cfDNA integrity0.68 (0.47, 0.91) ng/mL, CEA7.93 (3.21, 10.31) ng/mL and Cyfra21-1 5.75 (2.85, 8.12) ng/mL in the malignant pulmonary nodule group were significantly increased (P < 0.05). Plasma cfDNA concentration and integrity showed no significant correlation with gender, age, smoking or not, tumor diameter, pathological type, TNM stage, degree of tumor differentiation and lymph node metastasis in lung cancer patients (P>0.05). ROC curve showed that area under the curve, sensitivity and specificity of plasma cfDNA concentration and cfDNA integrity were higher or larger than those of CEA and Cyfra21-1, the sensitivity and specificity of plasma cfDNA concentration and cfDNA integrity combined with CEA and Cyfra21-1 in the diagnosis of NSCLC were higher than those of their single detection of plasma cfDNA concentration, cfDNA integrity, CEA, Cyfra21-1 (P < 0.05).

Conclusion  Plasma cfDNA and its integrity have certain clinical value in the diagnosis of benign and malignant pulmonary nodules, and can be used as molecular biological indicators for the auxiliary diagnosis of benign and malignant pulmonary nodules.