The Association Between Serum Leptin Levels and Cardiovascular Events in Patients With Rheumatoid Arthritis

Jiliang Chen, MD; Zhiping Xie, PhD; Zou Bin, MD


Lab Med. 2021;52(1):86-92. 

In This Article

Materials and Methods

Study Population

Between January 2014 and October 2015, we studied 223 patients with RA from the National Population Health Science Data Center in China. This database contains the original data of various medical industries in China, so this study has sufficient data to be analyzed. These patients were stable without other serious illnesses for more than 2 months before hospital admission. The diagnosis of RA was confirmed by 2 rheumatologists according to the 2010 American College of Rheumatology/European League Against Rheumatism Classification Criteria for RA.[20] The main reasons for the hospitalization of these patients with RA were extra-articular complications and/or self-required hospitalization because of their older age (median age = 68.1 years). All patients were treated with regular anti-RA therapy during hospitalization. Patients with neoplastic diseases, acute kidney disease or dialysis, serious liver diseases, or other serious diseases not associated with RA-related complications were excluded. Nine patients were excluded from the study because of severe liver and other malignant diseases. For the purposes of this study, the diagnosis of CVD history included myocardial infarction, heart failure (HF), stroke, and peripheral vascular disease. All clinical characteristic data on this study, including age, sex, body mass index (BMI), and history of smoking, drinking, and CVD, were obtained from patients' current or previous medical records in our hospital.

All included patients were followed up for a mean period of 40 months (range = 8–42 months). These patients with RA were followed for time-to-event analysis until occurrence of CV events (fatal and nonfatal events). The nonfatal CV events consisted of myocardial infarction, stroke, HF, and peripheral vascular disease. The fatal events were defined as CV death caused by myocardial infarction, stroke, HF, peripheral vascular disease, and sudden cardiac death. The diagnosis of all CV events was confirmed by the 2 attending physicians. These follow-up data were recorded by routine outpatient clinic visits and telephone contacts. According to Declaration of Helsinki guidelines, the Ethics Committee of the Affiliated Mindong Hospital of Fujian Medical University, Fu Jian, People's Republic of China, approved this prospective study, and all patients in our study gave written informed consent.

Measurement of Leptin

Venous blood specimens from patients with RA were collected the first morning after admission. The specimens were immediately prepared by centrifugation and processed with cryopreservation (–80°C) for testing leptin levels. Serum specimens were assayed in duplicate using an enzyme-linked immunosorbent assay (R&D Systems, Minneapolis, MN: Elisa Development System, Duoset Human Leptin, Catalog No. DY398) for measuring leptin levels. This assay measured the total amount of leptin present in a specimen, independent of the presence of leptin-binding proteins. The detection limit was 0.1 μg/L. The intra-assay variation was <3.5%, and the interassay variation was <6.4%, which suggested that the test method was reliable for the detection of leptin levels.

Laboratory Measurements and Definitions

The blood specimens collected from patients with RA the first morning after admission were also used for measuring serum creatinine (SCr), serum urea nitrogen (BUN), fasting blood glucose (FBG), albumin (ALB), high-sensitivity C-reactive protein (hs-CRP), total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL), and low-density lipoprotein cholesterol (LDL) with the use of the Siemens ADVIA 2400 automatic biochemistry analyzer (Siemens AG). Hemoglobin (Hb) was obtained by using an automated blood counter (Sysmex XE5000; Emilio de Azevedo Campos, Porto, Portugal). The homeostasis model assessment of insulin resistance (HOMA-IR) was used to calculate insulin resistance.

Statistical Analyses

All of the analyses were performed by using SPSS 23.0, and P ≤.05 was statistically significant. Normality of data was analyzed by the Kolmogorov-Smirnov test combined with Q-Q plots. The data that were not normally distributed were expressed by median (interquartile range) and were analyzed by the Mann-Whitney U test. Data were presented as mean ± standard deviation for normally distributed data and were analyzed by independent t-test. The distributions of categorical variables were studied by using the χ2 test. The associations of serum leptin levels with CVD history and CV events were analyzed by logistic regression and Cox proportional hazard analysis, respectively. The multivariate logistic regression analysis was performed to identify the independent association between serum leptin levels and CVD history in patients with RA at baseline. The Cox proportional hazard model was used to identify the independent prognostic factors for CV events. In the Cox proportional hazard analysis, the factors (P <.1) performed by univariate analysis were entered into the multivariate analysis. In addition, we also adjusted for clinical data relevant to CVDs even if these were not significantly associated with outcomes in the univariate analysis. The CV events-free curves were constructed according to the Kaplan-Meier method and were compared using the log-rank test.