ObjectiveTo explore the diagnostic value of serum cystatin C (CysC) and C1q tumor necrosis factor-related protein 9 (CTRP9) levels for diabetic retinopathy (DR) and diabetic macular edema (DME) in patients with type 2 diabetes.

MethodsA cross-sectional study was conducted.A total of 135 patients with type 2 diabetes, aged 45-75 years, who were treated in Gansu Provincial Hospital from April 2021 to April 2022 were included.According to DR grading standard, patients were divided into non-DR (NDR) group, non-proliferative DR (NPDR) group and proliferative DR (PDR) group, with 45 patients in each group.The DR patients were subdivided into DME group (51 cases) and non-DME group (39 cases).A total of 45 healthy subjects were selected as the normal control group.Fasting peripheral venous blood was collected to detect serum glycosylated hemoglobin, fasting blood glucose, triacylglycerol, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, CysC and CTRP9 levels.The expression of CysC and CTRP9 levels among different groups were compared.The independent influencing factors of DR and DME were evaluated by multivariate logistic regression analysis model.The diagnostic value of serum CysC and CTRP9 in DR and DME were evaluated by receiver operating characteristic (ROC) curve.This study adhered to the Declaration of Helsinki and the study protocol was approved by the Ethics Committee of Gansu Provincial Hospital (No.2021-301).All patients were informed about the purpose and methods of the study and signed an informed consent form.

ResultsSerum CysC levels in normal control group, NDR group, NPDR group and PDR group were 0.74(0.67, 0.83), 1.03(0.85, 1.22), 1.40(0.98, 1.63) and 1.66(1.31, 1.85)mg/L, respectively, showing a gradually increasing trend, and the serum CTRP9 levels were (136.90±14.95), (120.23±16.31), (109.50±14.71) and (90.99±13.88)pg/ml, respectively, showing a gradually decreasing trend, with statistically significant overall comparison differences among groups ( Z=89.430, P<0.001; F=74.242, P<0.001), the comparison within groups was statistically significant (all at P<0.05).Compared with non-DME group, the serum CysC level was significantly increased and serum CTRP9 level was significantly decreased in DME group (both P<0.05).Multivariate logistic regression analysis showed that serum CysC (odds ratio [ OR]=19.742, 95% confidence interval [ CI]: 4.515-86.316, P<0.001) was the independent risk influencing factors for the occurrence of DR, and CTRP9 ( OR=0.937, 95% CI: 0.908-0.966, P<0.001) was a protective factor for the occurrence of DR.Serum CTRP9 level ( OR=0.838, 95% CI: 0.778-0.903, P<0.001) was a protective factor for DME.The ROC curve showed that the area under ROC curve (AUC) for serum CysC and CTRP9 levels alone and in combination for the diagnosis of DR in patients with type 2 diabetes mellitus complicated by DR were 0.798, 0.802 and 0.870, respectively.The cutoff values of serum CysC and CTRP9 levels to obtain the best diagnostic efficacy were 1.34 mg/L and 110.12 pg/ml, respectively.The AUC for serum CysC and CTRP9 level alone and in combination for the diagnosis of DME in DR patients were 0.682, 0.923 and 0.923, respectively.The cutoff value of serum CTRP9 level to obtain optimal diagnostic efficacy was 104.68 pg/ml.

ConclusionsThe enhanced expression of serum CysC level and reduced expression of serum CTRP9 level are the risk factors for the development of DR in type 2 diabetes patients.The decrease of serum CTRP9 level is one of the risk factors for the development of DME in DR patients.