Rethinking Cardiovascular Risk: Medical Focus Shifts to 'Hidden' Blood Lipids Beyond HDL and LDL

Key facts

Reporting by Pat Hagan examines the limitations of the traditional two-part model of cholesterol classification—HDL versus LDL—and highlights growing concern over secondary lipid components that escape detection during routine clinical checkups.

In standard medical practice, a patient undergoing routine health screening receives a basic lipid panel. This test typically reports total cholesterol, HDL cholesterol, LDL cholesterol, and triglycerides. In many diagnostic laboratories, LDL cholesterol is not directly measured; instead, it is estimated using the Friedewald equation, developed in 1972, which calculates LDL by subtracting HDL and a fraction of total triglycerides (Triglycerides divided by 5) from total cholesterol.

This conventional approach can leave significant diagnostic blind spots. Specifically, it fails to measure several pathogenic lipid entities:

First, Lipoprotein(a), pronounced "L-P-little-a," is a specialized particle comprising an LDL-like core attached to a large protein called apolipoprotein(a). Due to structural similarities to plasminogen, elevated Lp(a) not only promotes the accumulation of fatty deposits inside arterial walls (atherogenesis) but also encourages blood clot formation (thrombosis) and arterial inflammation.

Second, remnant cholesterol refers to the cholesterol carried by triglyceride-rich lipoproteins after body tissues extract part of their triglyceride content. These particles—primarily intermediate-density lipoproteins (IDL) and very-low-density lipoprotein (VLDL) remnants—are small enough to penetrate the endothelial lining of blood vessels, contributing directly to plaque formation independently of standard LDL levels.

Third, Apolipoprotein B (ApoB) represents the total number of atherogenic particles in the bloodstream, as each LDL, VLDL, IDL, and Lp(a) particle carries exactly one ApoB molecule. Standard LDL concentration tests measure the total mass of cholesterol contained within LDL particles, not the absolute number of particles themselves. A patient with a high count of small, dense LDL particles may show a normal LDL cholesterol concentration on a standard report while carrying a dangerously high ApoB particle count.

Why it matters

The persistence of undetected lipid risk has major implications for clinical practice, patient outcomes, and healthcare economics.

For patients, relying solely on standard LDL readings can create a false sense of security. Individuals presenting with optimal LDL levels may still experience heart attacks or ischemic strokes—a phenomenon known in cardiology as residual cardiovascular risk. When hidden particles like Lp(a) or elevated remnants are present, silent arterial narrowing can progress unchecked for years despite reassuring standard test results.

For prescribing physicians, identifying these non-standard lipid fractions fundamentally alters treatment strategies. Standard first-line therapies for high cholesterol, such as statins, work by inhibiting the HMG-CoA reductase enzyme in the liver, which upregulates LDL receptors and clears circulating LDL particles. However, statins are largely ineffective at lowering Lipoprotein(a) levels and can sometimes cause modest increases in Lp(a) concentrations. Consequently, a patient whose cardiovascular risk is driven primarily by genetic Lp(a) elevation will derive limited protective benefit from standard statin therapy alone.

From a health economics perspective, expanding blood testing to include ApoB or Lp(a) requires diagnostic infrastructure updates and policy changes. Advanced lipid assays require distinct laboratory reagents and automated analyzers, incurring extra costs that public healthcare systems—such as the UK National Health Service (NHS)—and private medical insurers in the United States have historically restricted to high-risk individuals or specialist lipid clinics.

Understanding the current debate around hidden cholesterol requires reviewing the history of lipidology and cardiovascular risk assessment.

The foundation of modern preventive cardiology was established by the Framingham Heart Study, launched in 1948 in Framingham, Massachusetts. Over several decades, Framingham researchers identified elevated total serum cholesterol as a major risk factor for coronary heart disease. In the mid-20th century, biophysicist John Gofman and his colleagues used ultracentrifugation to separate plasma lipoproteins into distinct density classes, discovering HDL, LDL, and VLDL.

By the 1980s, large-scale clinical trials demonstrated that lowering LDL cholesterol significantly reduced the incidence of cardiovascular events. The approval of lovastatin by the US Food and Drug Administration (FDA) in 1987 ushered in the modern statin era, making lipid-lowering therapy a cornerstone of preventive medicine. Subsequent drug approvals included ezetimibe in 2002, which inhibits intestinal cholesterol absorption, and injectable PCSK9 inhibitors (such as evolocumab and alirocumab) in 2015, which dramatically lower LDL levels by preventing LDL receptor degradation.

Despite these therapeutic advances, residual cardiovascular risk remained prevalent. In 2019, the European Society of Cardiology (ESC) and the European Atherosclerosis Society (EAS) updated their clinical guidelines to recommend that every adult should have their Lipoprotein(a) level measured at least once in their lifetime to identify individuals with extremely high inherited cardiovascular risk. Similarly, joint guidelines from the American College of Cardiology (ACC) and the American Heart Association (AHA) recognized ApoB and Lp(a) as key "risk-enhancing factors" to guide clinical decisions when standard risk calculators yield ambiguous results.

Reaction

Medical organizations and lipidologists have increasingly advocated for expanding basic cardiovascular screening to incorporate advanced lipid markers. Preventive cardiologists argue that measuring ApoB provides a more accurate assessment of atherogenic risk than standard LDL cholesterol, particularly in patients with metabolic syndrome, type 2 diabetes, or high triglyceride levels.

However, primary care guidelines and public health agencies have been cautious about recommending universal screening for all non-traditional lipid markers. Health technology assessment bodies, including the National Institute for Health and Care Excellence (NICE) in the United Kingdom, weigh the clinical benefit of broad screening against the direct financial costs to national health systems.

Within the pharmaceutical industry, the recognition of hidden cholesterol as an unmanaged risk factor has triggered intensive drug development efforts. Biotechnology firms and global pharmaceutical companies are actively developing targeted nucleic acid therapies—including antisense oligonucleotides and small interfering RNA (siRNA) compounds—designed to selectively silence the LPA gene in the liver, reducing circulating Lp(a) levels by up to 80 to 90 percent.

What we don't know yet

Despite growing clinical awareness, key scientific and operational questions remain unresolved regarding hidden cholesterol particles.

First, while observational studies strongly associate elevated Lipoprotein(a) with increased rates of heart attack and aortic stenosis, it remains unproven whether therapeutically lowering Lp(a) directly reduces the incidence of major adverse cardiovascular events (MACE). Ongoing Phase 3 clinical outcome trials evaluating Lp(a)-lowering drugs are designed to answer this definitive question.

Second, global consensus is currently lacking regarding standardized diagnostic reference ranges for remnant cholesterol and ApoB across diverse patient demographics. Standardized assay calibration across international commercial laboratories remains incomplete, complicating universal clinical cut-offs.

Third, the long-term safety profile of chronic gene-silencing therapies targeting lipid pathways over multi-year treatment horizons requires ongoing monitoring through extended clinical studies.

What to watch

Several pivotal milestones will shape how hidden cholesterol is diagnosed and treated in clinical practice:

This report is based on reporting published by Pat Hagan.