Renal function had an independent relationship with coronary artery calcification in Chinese elderly men

This cross-sectional study was carried out in 105 male participants hospitalized in Chinese People’s Liberation Army General Hospital. All included were older than 60 years. Exclusion criteria were: 1) participants with previous percutaneous transluminal coronary angioplasty, coronary artery bypass graft, heart valve replacement or cardiac pacemaker implantation; 2) participants with a disorder affecting the bone and calcium metabolism, such as GFR < 45 ml/min/1.73 m², thyrotoxicosis, hyperparathyroidism, neoplasms or infectious diseases; and 3) participants with a drug affecting the bone and calcium metabolism, such as glucocorticosteroid, estrogen or bisphosphonates.

Detailed history and physical examination were performed on all participants at inclusion into the study. All participants were hospitalized and examined at stable ambient temperature. Height was measured in the standing position using a wall-mounted measuring tape, and body weight was measured with a digital scale wearing a standardized health check-up clothes. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared. Mean systolic and diastolic blood pressure (MSBP and MDBP) were measured using a standard mercury sphygmomanometer with participants in a seated position after having quietly rested for 10 minutes. Hypertension was defined as MSBP ≥ 140 mmHg, MDBP ≥ 90 mmHg or receiving the anti-hypertensive drugs. CAD was characterized by the positive diagnostic procedure (stress test, computed tomography, radionuclide image and coronary angiography), and the presence of angina pectoris or myocardial infarction. Participants with atypical angina pectoris or suspected CAD received the examination of stress test in the same room using the same equipment (T-2100 Treadmill, GE Healthcare, Wisconsin, USA), and evaluated by the consensus of two experienced cardiologists. Routine biochemistry was performed on fasting serum sample collected in the morning. Biochemistry values, including triglyceride, low density lipoprotein-cholesterol (LDL-c), high density lipoprotein-cholesterol (HDL-c), fasting blood glucose (FBG), uric acid, calcium and phosphorus, were tested by an automatic analyzer (Cobas® 6000, Roche, Basel, Switzerland). GFR values were determined by Chinese modified Modification of Diet in Renal Disease equation and used for the determination of renal function: 175 × serum creatinine (mg/dl)^-1.234 × age (year)^-0.179 × 0.79 (if female) [12].

Participants underwent the scans of HDCT (Discovery CT 750 HD, GE Healthcare, Wisconsin, USA). All scans were performed in the same room using the same equipment, and analyzed by the consensus of two radiologists with more than two years of experience blinded to all participants and prior information. For defining the quantity of coronary calcium, the Agatston, volume and mass scores were calculated using the software (Smart Score 4.0, GE Healthcare, Wisconsin, USA) on the three-dimensional workstation (Advantage Windows Workstation 4.5, GE Healthcare, Wisconsin, USA), according to the following equations: 1) Agatston score = slice increment/slice thickness × ∑(area × cofactor); 2) volume score = ∑(area × slice increment); and 3) mass score = ∑(area × slice increment × mean CT density) × calibration factor [13, 14]. The sum of all scores for each coronary artery including left main artery, left anterior descending artery, left circumflex artery and right coronary artery was used to generate the total CAC scores (Fig. 1).

Descriptive statistics for the continuous variables with normal distribution were presented as mean ± standard deviation and for the categorical variables were presented as number and percentage. Participants were classified into three groups according to the GFR tertiles as follows: tertile 1 (>86.2 mL/min/1.73 m²), tertile 2 (76.2–86.2 mL/min/1.73 m²) and tertile 3 (< 76.2 ml/min/1.73 m²). Statistical comparison for these groups was conducted using the one-way analysis of variance (ANOVA) for the continuous variables with normal distribution and chi-squared test for the categorical variables. Pearson’s correlation for the continuous variables with normal distribution and Spearman’s correlation for the categorical variables were used to evaluate their simple relationship with CAC scores. Multivariate linear regression analysis (enter) was undertaken after adjusting for age, BMI, CAD, hypertension, MSBP, MDBP, heart rate, triglyceride, LDL-c, HDL-c, FBG, uric acid, calcium and phosphorus values. All analyses were two-sided with p value < 0.05 considered statistically significant, and performed using the Statistical Package for the Social Sciences version 17 (SPSS, Inc, Chicago, IL, USA).