The Role of the Atherogenic Index of Plasma and the Castelli Risk Index I and II in Cardiovascular Disease

Introduction: Metabolic syndrome (MS), identified by abdominal obesity, insulin resistance, hypertension, and/or dyslipidemia, occurs across all BMI (body mass index) ranges and increases the risk of atherosclerotic cardiovascular (CV) diseases and type II diabetes. The Atherogenic Index of Plasma (AIP) and Castelli Risk Index (CRI) I & II are ratios that can be calculated from a simple lipid profile test. These ratios are independent risk factors for CV diseases and have been shown to be increased in angiographically confirmed coronary artery disease (CAD) patients. This study aimed to assess CV risk across the different subtypes of obesity: metabolically obese non-obese (MONO), metabolically healthy non-obese (MHNO), metabolically obese obese (MOO), and metabolically healthy obese (MHO) using AIP and CRI I & II and to study the association of AIP, CRI I & II with other CV risk factors such as total body fat percentage (BF%), visceral fat percentage (VF%), and BMI. Assessing CV risk in an individual based on the person's subtype of obesity using ratios calculated from simple lipid profile parameters may prove beneficial to developing better screening strategies.

Methods:  A cross-sectional study was conducted on 128 adults with BMI ≥18.5 kg/m with and without MS, presenting to the General Medicine/Internal Medicine Outpatient Department in M S Ramaiah Medical College Hospital, Bangalore, Karnataka State, India. The sample size was calculated to be a minimum of 82 subjects based on a study that showed that AIP and CRI I & II had a positive association with BMI. After a detailed history, physical examination, anthropometric measurements (height, weight, and waist circumference), VF%, and BF% by bio-impedance were recorded. A blood sample was processed for lipid profile and fasting blood sugar on a Vitros 5600 auto-analyzer (Quidel Corporation and Ortho Clinical Diagnostics, San Diego, CA, USA). Subjects were divided into MONO (non-obese subjects with BMI < 25 kg/m having MS), MHNO (no obesity or MS), MOO (obese BMI ≥ 25 kg/m having MS), and MHO (obese BMI ≥ 25 kg/m not having MS) groups. AIP and CRI I & II were calculated. Statistical analysis was performed using the chi-square test, ANOVA, Pearson correlation coefficient, and receiver operating characteristic curve (ROC).

Results:  MONO, MHNO, MOO, and MHO constituted 26 (20.3%), 48 (37.5%), 28 (21.8%), and 26 (20.3%) of the 128 subjects, respectively. AIP ≥0.24 was found in 16 (61.5%) of MONO and in 16 (51.1%) of MOO subjects. CRI-I >4 was found in 19 (73.1%) and 16 (57.1%) subjects of the MONO and MOO groups, respectively. Eleven (42.3%) and 12 (42.9%) of MONO and MOO subjects, respectively, had CRI-II >3. Pearson's correlation revealed for AIP r=0.32, p=0.000 and r=0.43, p=0.000 with VF% and BMI, respectively. The area under the curve (AUC) for AIP and CRI I & II to detect the presence of MS were 0.84, 0.74, and 0.73, respectively.

Conclusion: CV risk, as assessed by AIP and CRI I & II in the different subtypes of obesity, was found to be highest in the MONO group, followed by the MOO group. With BMI and VF%, AIP showed a moderately positive linear correlation. API and CRI could be tools of low cost and moderate reliability in screening the general population for risk of CV disease.