Advanced Cholesterol Testing

I was originally planning on starting to talk about medicines used to lower Triglycerides but due to the untimely death of Tim Russert, I wanted to discuss Advanced Cholesterol Testing. Last week I had the great pleasure of being interviewed on a nationally syndicated radio show. I was asked what I believed could be done to bring more awareness to physicians and the public about the epidemic of Cardiovascular morbidity and mortality? The entire podcast is available on my website and the feedback that I have received from my patients was that I took a difficult topic and made it so easy to understand for the average person. I hope that after listening and reading this posting you will see the need to perform this special type of cholesterol testing.

Over three years ago, I opened The Center for Cholesterol Management as the only free standing lipid clinic in the Los Angeles area dedicated to Advanced Lipoprotein Particle Testing. As a board certified Cardiothoracic surgeon, I feel I have a unique perspective about coronary artery disease in that I am able to clinically correlate angiographic findings with actual operative findings which in so many incidences are discordant. Coronary artery disease is a largely misunderstood entity.

Hyperlipidemia is the most modifiable risk factor leading to Atherosclerosis, yet traditional lipid testing may miss up to 50% of people who have abnormal lipids. Prevention includes identifying people at risk and providing the best treatment individualized to their specific problem.

It is with this background that I will discuss Advanced Lipid Testing and its role in identifying all patients at lipid related risk and as a tool for management of abnormal lipid levels. I often ask myself how come health care providers do not understand this type of testing? I honestly believe that if all people are identified as being at risk, and then if treated appropriately, we would significantly change the face of Cardiovascular morbidity and mortality.

As physicians, we are taught in medical school that it is all about Total Cholesterol, HDL-C, LDL-C, and Triglycerides, yet few really understand the limitations of traditional lipid testing. I hear everyday physicians say that if it is so important why isn't everyone doing it? I believe the answer is that one does not want to change from old patterns of thinking, and according to other physicians, it is too much trouble to learn and understand. Recently, the ADA/ACC released a Joint Concession Statement on Lipoprotein Management in patients with Cardiometabolic Risk(CMR). The full text is available on my website. I believe it is mandatory reading and states that patients with CMR in the moderately high, high, and very high risk groups, it is now the standard of of care to quantify lipoproteins by performing ApoB or LDL-P on all patients to ascertain risk and as a goal of therapy.

As we all know that since sterols are insoluble in the blood, they need to be driven around the body in Lipoproteins. These include HDL-P, VLDL-P, and LDL-P among others. HDL particles are also known as ApoA and all the particles that cause atherosclerosis are known as ApoB. Although NCEP( National Cholesterol Education Panel) recommends calculating the non-HDL cholesterol, this value only can alert the physician that there may too many lipoprotein particles despite having a normal LDL-C. Approximately 90-95% pf the circulating ApoB particles are LDL-P which have a half-life of around 3 days. As varying amounts of Triglycerides and Cholesterol are driven around the body, in what I tell my patients are "cars", the ApoB particles enter the arterial wall if there are too many of the "cars" circulating in the bloodstream.

By simple diffusion, all the bad particles flow from inside the artery and move into its wall and are "eaten" by macrophages which become foam cells and are the hallmark of Atherosclerosis. In eight published studies of over 11,000 subjects using LDL-P and other Lipoprotein concentrations remained the most significant and independent predictor of cardiovascular morbidity and mortality over any other lipid parameter including the usual ratio that all physicians and patients talk about. . In a nutshell, it is the number of LDL particles that matter most... it is the number of cars that cause a traffic jam, not the people in the cars. For example, what if a person with moderate risk has met NCEP guidelines and has a LDL-C of 110mg/dl.

How do I know that there are not 100 cars with one person driving or two big buses with 55 people? The answer is that I do not unless I measure LDL-P directly by using NMR or as a second option measuring ApoB with Gel Electrophoresis. Traditional testing measures the passengers and lipoprotein testing measures the cars, and it is the number of cars(LDL-P) measured by NMR (Nuclear Magnetic Resonance) that are the most numerous ApoB particles in the body and matter most in the development of Atherosclerosis.

Although a comprehensive review of each of the methodologies to perform Lipoprotein Testing is beyond the scope of this post, I feel that measuring LDL particles directly using NMR is the best way to ascertain someone's true risk and then use that number as a guide to management. As I said in my posting about Alex Trebek, the CDC states that 50% of people who have heart attacks have "normal" cholesterol. I hope you now understand why this can happens, having a normal LDL-C but high LDL-P, and be proactive and ask that your physician performs Advanced Cholesterol Testing.

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• Are You at Risk for a Heart Attack?
• Heart Disease and Diabetes: Don't Be a Statistic

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Lowering LDL Cholesterol: Bile Acid Sequestrants

The next group of Gastrointestinally Active Lipid Lowering Drugs I will talk about are the Bile Acid Sequestrants (BASs). Like Zetia, this class of drugs works in the intestines. They have been used since the 1960s. Since they are not absorbed into the body they are inherently safe and also safe during pregnancy.

They are a good class of drugs for young adults contemplating a potential lifetime of exposure to a medication and are the only class of drugs recommended by NCEP for use in children. The three most common adverse events that have been reported are constipation, rarely leading to obstruction, increase in plasma triglyceride levels, and decrease absorption of some medicines and certain vitamins. The newest agent, Colesevelam (Welchol)-available as a tablet, has greater affinity for bile acids compared with the older medicines such as Cholestyramine(Questran)-available as a powder, so it has fewer drug interactions and is less likely to cause constipation.

The main problem with this class of drugs for patients with hypercholesterolemia can be the taste, the amount that needs to be taken, and the bloating and constipation. I tell my patients to take a stool softener while on this class of drugs or to drink prune juice. Since the development of Welchol and the improved gastrointestinal tolerance, more patients are willing to take BASs. In an analysis of 3 randomized, placebo-controlled trials of Welchol added to statin therapy, constipation was only reported in less than 10% of patients and less than 5% withdrew secondary to side effects.

These classes of drugs are anion-exchangers and cause increased clearance of LDL-C from the blood. As I said previously, they work in the intestines by binding bile acids, and thus, interrupt the circulation of bile acids back to the liver. Since there is less bile acid available, cholesterol is converted to bile acid and the concentration of cholesterol within the liver falls. As this happens, LDL receptor activity of the liver cell increases which then increases LDL clearance from the blood.

The largest set of data on Bile Acid Sequestrants comes from the Lipid Research Clinics Coronary Primary Prevention Trial (LRC-CPPT). Reduction in coronary risk corresponded to LDL-C reduction. When the maximum dose of 24 grams/day of Cholestyramine was used, there was 28% reduction in LDL-C and a 39% reduction in CHD risk. The BASs have been used alone or in combination with other lipid lowering medications in one major trial with a clinical endpoint and in five with angiographic endpoints.

BASs should be avoided in patients with TGs greater than 400mg/dl because they tend to raise TG levels. If it is be used in combination with medicines to lower TGs, this is not a major concern but if used alone should only be used if one's TG level is less than 200mg/dl.

Finally, due to potential drug interactions, coumadin, thiazide diuretics, propanolol, tetracycline, penicillin G, phenobarbital, thyroid preparations, estrogens, progestins, and digoxin should be administered one hour before or four hours after taking the older BAS agents. The current evidence has shown that Welchol can be taken concurrently with these medicines. The next class of drugs we will explore in the coming weeks will be fibrates.

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