Study design and Population
This is a prospective observational study at the Department of Interventional Cardiology, Thong Nhat Hospital in Ho Chi Minh City, Vietnam. Consecutive patients were recruited from September 2019 to May 2020. Inclusion criteria included: (1) age ≥ 60 years, (2) undergoing coronary angiography and/or PCI, (3) with recorded serum creatinine levels before and in 48 hours after angiography. Patients were excluded from this study if (1) they were concomitantly using other nephrotoxic medications, (2) they were transferred to another hospital, or were discharged, or died within 48 hours after the procedure, or (3) they did not provide consent.
Data collection
Data were collected from patient interviews and medical records. Information obtained included: demographic characteristics, height, weight, medical history, comorbidities, admission diagnosis, laboratory results during hospitalisation including serum creatinine levels, and the contrast volume used during the procedure. Age and sex were used as recorded in medical records. Body mass index (BMI, kg/m2) was calculated based on measured weight (kg) and height (m) and was classified into 4 groups: underweight (BMI < 18.5 kg/m2), normal (BMI 18.5–22.9 kg/m2), overweight (BMI 23-24.9 kg/m2), and obese (BMI ≥ 25.0 kg/m2). Smoking status was categorised based on self-reporting as non-smoking or smoking (including current smokers or ex-smokers who stopped smoking less than 1 year ago).
Outcome variable: CIN was defined as a 25% increase in serum creatinine from baseline or 0.5mg/dL absolute increase in serum creatinine occurring within 48 hours post IV contrast administration.
CIN risk prediction models:
The Contrast volume-to-GFR ratio (CV/GFR ratio): CV/GFR ratio was calculated as the ratio of contrast quantity received to the patient’s GFR. The GFR was estimated using the Cockcroft-Gault method: 140 – age (years) x weight (kg) / (72 x serum creatinine (mg/dl) {x 0.85 for female participants}.13 In a large observational study in the USA involving 3179 consecutive patients undergoing PCI (mean age 64 ± 12), a CV/GFR ratio > 3.7 was a significant and independent predictor of an early abnormal increase in serum creatinine after PCI.14
The Mehran score was developed by Mehran and colleagues in 2004. This risk score includes hypotension (if systolic blood pressure < 80 mmHg for at least 1 h requiring inotropic support 5 points), use of intra-aortic balloon pump (5 points), congestive heart failure (if class III/IV by New York Heart Association classification or history of pulmonary edema: 5 points), age (if > 75 years: 4 points), anemia (if hematocrit < 39% for men and < 36% for women: 3 points), diabetes mellitus (3 points), contrast media volume (1 point per 100 mL), and estimated glomerular filtration rate (GFR; GFR in mL/min per 1.73 m2; 2 points, if GFR 60 to 40; 4 points, if GFR 40 to 20; 6 points, if GFR < 20). A risk score < 5 indicated low CIN risk, while 6–15 indicated intermediate, and 16 or more indicated high risk.8
Sample size justification: The sample size was determined using a single population proportion formula: n = Z2 1− α/2 * [p*(1-p)/d2], with n = the required sample size, Z1− α/2 = 1.96 (with α = 0.05 and 95% confidence interval), p = estimated rate of CIN in older patients after PCI, and d = precision (assumed as 0.05). Our literature search found only one previous study in Vietnam reporting an incidence of approximately 13% in older adults (mean age 68.9 ± 9.9) after PCI.15 Therefore, the sample size for our study was estimated to be around 170 participants.
Statistical Analysis
Analysis of the data was performed using SPSS for Windows (version 27.0, IBM Corp., Armonk, NY, USA) and R 4.1.1. Continuous variables are presented as means ± standard deviation, and categorical variables as frequencies and percentages. Comparisons between groups were conducted using the Chi-square test or Fisher’s exact test for categorical variables and Student’s t-test or Mann-Whitney test for continuous variables.
Receiver Operator Characteristic (ROC) was applied to evaluate the area under the curve (AUC) of the CV/GFR ratio and Mehran score in predicting CIN and to determine the cut-off points of the scores. A higher AUC value suggests a better diagnostic ability. An AUC of 0.5 suggests no discrimination (i.e., ability to diagnose patients with and without CIN based on the test), 0.7 to 0.8 is considered acceptable, 0.8 to 0.9 is considered excellent, and more than 0.9 is considered outstanding.16