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Circulation. 2019;139:e1082–e1143. DOI: 10.1161/CIR.0000000000000625 June 18/25, 2019 e1087 CLINICAL STATEMENTS AND GUIDELINES

1.5 Class of Recommendation and Level

of Evidence

Recommendations are designated with both a class of recommendation (COR) and a level of evidence (LOE). The class of recommendation indicates the strength of recommendation, encompassing the estimated magnitude and certainty of benefit in proportion to risk. The level of evidence rates the quality of scientific evidence supporting the intervention on the basis of the type, quantity, and consistency of data from clinical trials and other sources (Table 2).S1.5-1

1.6 Abbreviations

Abbreviation Meaning/Phrase ABI ankle-brachial index ACS acute coronary syndrome AIDS acquired immunodeficiency syndrome apoB apolipoprotein B ARR absolute risk reduction ASCVD atherosclerotic cardiovascular disease CAC coronary artery calcium CHD coronary heart disease CK creatine kinase CKD chronic kidney disease COR Class of Recommendation CTT Cholesterol Treatment Trialists CVD cardiovascular disease eGFR estimated glomerular filtration rate FH familial hypercholesterolemia HDL high-density lipoprotein HF heart failure HIV human immunodeficiency virus LDL-C low-density lipoprotein cholesterol LOE Level of Evidence Lp(a) lipoprotein (a) MI myocardial infarction PCE pooled cohort equations QALY quality-adjusted life-year RA rheumatoid arthritis RCT randomized controlled trials RRR relative risk reduction RWI relationships with industry and other entities SAMS statin-associated muscle symptoms SR systematic review TC total cholesterol VLDL very low-density lipoprotein VLDL-C very low-density lipoprotein cholesterol 2 HIGH BLOOD CHOLESTEROL AND

ASCVD

2.1 Serum Cholesterol, Lipoproteins, and

ASCVD

2.1.1. Cholesterol, Lipoproteins, and Apolipoprotein B Serum cholesterol and its lipoprotein carriers (LDL, very low-density lipoprotein [VLDL], and HDL) are known to be related to ASCVD. LDL-C is the dominant form of atherogenic cholesterol. VLDL is the chief carrier of triglycerides, and VLDL cholesterol (VLDL-C) is also atherogenic. HDL-C is seemingly not atherogenic. Chylomicrons transport dietary fat; chylomicron atherogenicity is uncertain. The combination of LDL-C and VLDL-C is called non–HDL-C and is more atherogenic than either lipoprotein alone. The main protein embedded in LDL and VLDL is apolipoprotein B (apoB), and like non–HDL- C, apoB is a stronger indicator of atherogenicity than LDL-C alone.

2.1.2 Cholesterol, LDL-C, and ASCVD

Evidence that serum cholesterol contributes to ASCVD comes from several sources: animal studies, genetic forms of hypercholesterolemia, epidemiological studies, and RCTs. US population studiesS2.1.2-1,S2.1.2-2 suggest that optimal total cholesterol levels are about 150 mg/ dL (3.8 mmol/L), which corresponds to an LDL-C level of about 100 mg/dL (2.6 mmol/L). Adult populations with cholesterol concentrations in this range manifest low rates of ASCVD.S2.1.2-3 RCTs of cholesterol-lowering drugs in high-risk patients confirm that LDL-C lowering produces marked reductions in ASCVD. This confirms the general principle that “lower is better” for LDL- C.S2.1.2-4–S2.1-6 The present guideline looks to evidence from new RCTs to aid in the translation of RCT data to the individual patient to provide net benefit.S2.1.2-7

2.1.3 LDL-C and Other Risk Factors

Although LDL-C is a primary cause of atherosclerosis, other risk factors contribute, as well. The major risk factors include cigarette smoking, hypertension, dysglycemia, and other lipoprotein abnormalities. Because atherosclerosis progresses with advancing age, a person’s age also counts as a risk factor. By combining all major risk factors into a prediction equation, an individual’s probability of developing ASCVD can be estimated. The Framingham Heart StudyS2.1.3-1 took the lead in creating risk-prediction equations. These were improved in the 2013 ACC/AHA cholesterol guidelinesS2.1.3-2 by compiling data from 5 community-based cohorts that were broadly representative of the US population. These so-called population cohort equations have been validated in a large community-based US population.S2.1.3-3 Initially, data from the Women’s

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