Easy Guide To Understanding Blood Work/Definitions

Total Cholesterol

Your total cholesterol level is the overall amount of cholesterol found in your blood. It consists of low-density lipoproteins (LDL) and high-density lipoproteins (HDL). LDL is also called “bad” cholesterol because it blocks your blood vessels and increases your risk of heart disease.


Lipoproteins are combinations of lipids (fats) and proteins. They are the form in which lipids are transported in the blood. The high density lipoproteins transport cholesterol from the tissues of the body to the liver so it can be gotten rid of in the bile.

HDL cholesterol is therefore considered the "good" cholesterol. The higher the HDL cholesterol the lower the risk of coronary artery disease.


Low-density lipoprotein cholesterol, commonly referred to as 'bad' cholesterol. Elevated LDL levels are associated with an increased risk of heart disease. Lipoproteins, which are combinations of fats (lipids) and proteins, are the form in which lipids are transported in the blood.


The major form of fat stored by the body. A triglyceride consists of three molecules of fatty acid combined with a molecule of the alcohol glycerol. Triglycerides serve as the backbone of many types of lipids (fats). Triglycerides come from the food we eat as well as from being produced by the body.

Triglyceride levels are influenced by recent fat and alcohol intake, and should be measured after fasting for at least 12 hours. A period of abstinence from alcohol is advised before testing for triglycerides.

Elevated triglyceride levels are considered to be a risk factor for atherolsclerosis (hardening of the arteries) because many of the triglyceride-containing lipoproteins that transport fat in the bloodstream also transport cholesterol, a known contributor to atherosclerosis.

Markedly high triglyceride levels (greater than 500mg/dl) can cause inflammation of the pancreas (pancreatitis). Therefore, these high levels should be treated aggressively with low fat diets and medications, if needed.

The word "triglyceride" reflects the fact that a triglyceride consists of three ("tri-") molecules of fatty acid combined with a molecule of the alcohol glycerol ("-glyceride") that serves as the backbone in many types of lipids (fats).

ApoA1 (Apolipoprotein A-I)

The major protein component of HDL (high density lipoprotein) and a relatively abundant plasma protein. APOA-I is instrumental in promoting the transfer of cholesterol into the liver where it is metabolized and then excreted via the intestine from the body. The gene locus for APOA-I is on chromosome 11q23. A number of genetic variants of APOA1 are known, including ApoA-I Milano.

ApoB (Apoliprotein B)

gene on chromosome 2p24-p23 that encodes apolipoprotein B, the main apoliprotein of chylomicrons andlow-density lipoproteins, which appears in plasma as two main isoforms: apoB48 (which is synthesised exclusively in thegut) and apoB100 (which is synthesised in the liver).

APOB mutations cause hypobetalipoproteinaemia, normotriglyceridemic hypobetalipoproteinaemia, andhypercholesterolaemia due to ligand-defective apoB.

LP(a) (Lipoprotein(a))

A lipoprotein subclass. Genetic studies and numerous epidemiologic studies have identified Lp(a) as a risk factor for atherosclerotic diseases such as coronary heart disease and stroke.

Omega-3 Fatty Acids

A class of essential fatty acids found in fish oils, especially from salmon and other cold-water fish, that acts to lower the levels of cholesterol and LDL (low-density lipoproteins) in the blood. (LDL cholesterol is the "bad" cholesterol.)

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are the two principal omega-3 fatty acids. The body has a limited ability to manufacture EPA and DHA by converting the essential fatty acid, alpha-linolenic acid (ALA) which is found in flaxseed oil, canola oil or walnuts.

Omega-3 fish oil is considered a nutraceutical, a food that provides health benefits. Eating fish has been reported, for example, to protect against late age-related macular degeneration, a common eye disease. The American Heart Association recommends eating fish (particularly fatty fish such as mackerel, lake trout, herring, sardines, albacore tuna, and salmon) at least two times a week.

Free Fatty Acids

Molecules that are long chains of lipid-carboxylic acid found in fats and oils and in cell membranes as a component of phospholipids and glycolipids.

Lipid Particle Numbers

Low-density lipoproteins (LDL) are particles that transport lipids throughout the body. Each particle contains a combination of protein, cholesterol, triglyceride, and phospholipid molecules. Their composition changes as they circulate in the blood. Some molecules are removed and others are added, resulting in lipoprotein particles whose properties vary from large and fluffy to small and dense. LDL particle testing determines the relative amounts of particles of differing properties in the blood. This is often called subfraction testing.

The Quebec Cardiovascular Study was the first large study demonstrating that heart attack can occur when a person’s LDL particle number is high and LDL level is low.8 This has been repeatedly confirmed in other studies, most recently in the AMORIS study, which enrolled a remarkable 175,000 participants and demonstrated the superiority of LDL particle number (measured as apoprotein B) in predicting heart attack risk.9 This measure can be thought of as actually counting the number of LDL particles in one cubic centimeter, or one milliliter of blood.

LDL particle number is among the most powerful tools we have to predict the risk of heart attack. It can be measured directly as LDL particle number by the nuclear magnetic resonance spectroscopy method or indirectly as apoprotein B, which is a more widely available method. Apoprotein B is the major protein particle of LDL, with a single protein per LDL particle. Apoprotein B thus provides a “count” of LDL particles.

How can LDL level be low when the particle number is high? Because the amount of cholesterol contained per particle can vary widely. If you have many LDL particles that contain less cholesterol in each particle, the conventionally measured LDL level will be low, but your heart disease risk will be high. Greater numbers of cholesterol-containing particles in the blood means more cholesterol deposition in plaque. The combination of low LDL level and high LDL particle number is very common, creating a situation whereby many people are mistakenly told that they are not at risk for heart attack.

High LDL particle number responds to the same treatments as high LDL level, but this method of assessment provides greater confidence in determining who to treat and how intensively to do so. Statin prescription drugs lower LDL particle number, as does the non-statin prescription drug ezetimibe, though it is less potent. Niacin (vitamin B3) lowers LDL particle number less potently than the statins, but will achieve a 10-20% reduction. In addition to prescription medicines, many nutritional strategies can lower LDL particle number.

High LDL particle number can be a source of danger even when LDL level has been reduced by treatments such as cholesterol-lowering statin drugs. This is why people who take a cholesterol-lowering medication can still suffer a heart attack. LDL particle number provides much more powerful feedback on the adequacy of treatment and is therefore a tool for further reduction of risk.

Lipid Particle Sizes

LDL particles vary in size—big, medium, and small. The size difference is crucial. Small LDL particles are a far more destructive force than their larger counterparts. Like finely tuned weapons designed to wreak maximum damage, smaller particles more effectively penetrate the cellular barrier and enter arterial walls, contributing to atherosclerotic plaque. They also persist longer in the circulation, which allows more opportunity to cling like little magnets to tissues within the walls.

Once in the arterial wall, small LDL particles are more prone to oxidation, which stimulates the release of inflammatory and adhesive proteins. Small, dense LDL promotes endothelial dysfunction and enhanced production of pro-coagulants by endothelial cells. Small, dense LDL thus appears to be more atherogenic—that is, more likely to contribute to the build-up of plaque within arteries—than normal LDL.

Small LDL can be an inherited predisposition that is activated by unhealthy lifestyles and weight gain. When the genetic factors are strong, it can occur in healthy people who are not overweight. It frequently causes heart disease and is found in more than half of all people who suffer heart attacks. Small LDL particles triple the likelihood of developing coronary plaque and suffering a heart attack.

This one little measure also holds a world of hidden information. Not only does it indicate a higher risk for heart attack, but small LDL suggests that you are more resistant to insulin and more likely to develop metabolic syndrome, or even diabetes, if you become overweight. It also suggests that a very low-fat diet (deriving less than 20% of calories from fat) may paradoxically heighten your heart disease risk.

Small LDL can augment the dangers of other cardiac risk factors, such as high total cholesterol, increased LDL particle number, or high C-reactive protein (a measure of inflammation). Researchers have noted that while elevated small LDL particle count alone can raise heart attack risk by up to 300%, heart attack risk is sixfold higher (600%) when elevated C-reactive protein is also present.

Despite its dangers, small LDL is easy to treat. Weight loss is a powerful way to increase LDL particle size. Exercise also provides a modest benefit. Niacin in doses of 500-1500 mg daily (depending on your weight and genetic factors) effectively corrects LDL size. In doses exceeding 500 mg/day, niacin is best prescribed by a physician who is experienced with its peculiar, mostly harmless side effects, like feeling flushed or itchy. Slow-release preparations are available, but consult your doctor in choosing forms that have been shown to be safe. Exercise may also help to optimize lipoprotein profiles.20

Dietary strategies that slow or reduce sugar release into the bloodstream can be helpful. These include high-fiber foods and foods with a low glycemic index, as well as supplements such as flaxseed,glucomannan, oat bran, psyllium fiber, raw nuts like almonds and walnuts, and the “starch blocker” white bean extract.21

Oat bran is a great way not only to lower LDL particle number, but also to increase LDL particle size. Add two tablespoons daily to yogurt, fruit smoothies, cereal, or other foods.22 Omega-3 fatty acids from fish oil increase LDL size modestly, particularly if triglyceride levels are high.

HDL and HDL Subclasses

Many people with low HDL have been told their heart disease has no known cause or that its cause is untreatable. Both statements are simply untrue. Low HDL (below 40 mg/dL) is common, affecting more than half of all people with heart disease. Deficiency of the protective subclass within HDL is even more common, affecting most people with heart disease.

Like LDL, HDL comprises a family of HDL particles. The truly beneficial HDL is “large” HDL, sometimes also known as “HDL2b.” Large HDL is responsible for “reverse cholesterol transport,” or the extraction of cholesterol from plaque. Large HDL therefore plays a protective role and is crucial for regression (shrinkage) of coronary plaque.

As a rule, a deficiency of protective large HDL goes hand in hand with low total HDL levels of less than 40 mg/dL. In other words, if your HDL is less than 40 mg/dL, you are highly likely to have a marked deficiency of protective large HDL. If your total HDL is above 60 mg/dL, you probably have a favorable quantity of large HDL. If you are between 40 and 60 mg/dL, you may or may not have a deficiency of protective large HDL. Lipoprotein assessment is then necessary to measure large HDL.

Strategies that increase total HDL will also increase one’s proportion of large HDL. Strict low-fat diets (less than 20% of calories from fat) lower HDL and push HDL to the undesirable smaller size. Low-fat diets are therefore not advised when total HDL is low or when large HDL is deficient. People with low HDL do better by adding dietary sources of plentiful monounsaturated fatty acids (especially raw nuts, flaxseed products, and olive and canola oils), eating unprocessed foods with a low glycemic index, and increasing lean protein intake.28 Omega-3 fatty acids from fish oil have a modest effect in raising total HDL and increasing large HDL.29 The medical treatments to raise HDL are identical to those used to treat small LDL

Intermediate-Density Lipoproteins (IDL)

While many health-conscious adults are familiar with low-density lipoprotein (LDL) and high-density lipoprotein (HDL), they may not be aware of intermediate-density lipoprotein, or IDL. Though intermediate in density, there is nothing “intermediate” about IDL as a risk factor for heart disease. IDL is a potent contributor to heart attack risk. Elevated IDL means that the body struggles to clear fat from the blood after eating, with many more hours required to clear the blood than normal. The longer these lipoproteins persist in the blood, the more opportunity they have to create plaque, which may ultimately lead to a heart attack.

Only about 10% of people with heart disease have elevated IDL levels. While there is no specific treatment for high IDL, it does respond to a broad variety of treatments, particularly cholesterol-lowering medicines, niacin, fish oil, and weight loss. Knowing that you have a high IDL may mean that your treatment needs to be intensified, as IDL may persist even when LDL or other parameters are corrected.

AST (aspartate aminotransferase; also known as serum glutamic oxaloacetic transaminase (SGOT))

AST is an enzyme that is normally present in liver and heart cells. AST is released into blood when the liver or heart is damaged. The blood AST levels are thus elevated with liver damage (for example, from viral hepatitis) or with an insult to the heart (for example, from a heart attack). Some medications can also raise AST levels.

ALT (alanine aminotransferase)

An enzyme normally present in liver and heart cells that is released into the bloodstream when the liver or heart is damaged. The blood ALT levels are elevated with liver damage (for example, from viral hepatitis) or with an insult to the heart (for example, from a heart attack). Some medications can also raise ALT levels.

Total Bilirubin

A yellow to orange bile pigment produced by the breakdown of heme and reduction of biliverdin; it normally circulates inplasma and is taken up by liver cells and conjugated to form bilirubin diglucuronide, the water-soluble pigment excreted in thebile. 

Bilirubin. The metabolism of bilirubin. Once bile is taken up and conjugated bythe liver, some leakage of bilirubin mono- and diglucuronides does occur, butthese normally account for less than 5% of circulating bilirubin. In bile, morethan 80% is conjugated as the diglucuronide form. From Aspinall and Taylor-Robinson, 2001.

Failure of the liver cells to excrete bile, orobstruction of the bile ducts, can cause anincreased amount of bilirubin in the body fluids and lead to obstructive jaundice.


The main protein in human blood and the key to regulating the osmotic pressure of blood. Chemically, albumin is soluble in water, precipitated by acid, and coagulated by heat.

Total Protein

The total protein test measures the total amount of two classes of proteins found in the fluid portion of your blood. These are albumin and globulin.

Proteins are important parts of all cells and tissues.

Albumin helps prevent fluid from leaking out of blood vessels.

Globulins are an important part of your immune system.

DHEA (dehydroepiandrosterone)

A a steroid hormone made by the adrenal glands, that acts on the body much like testosterone and is converted into testosterone and estrogen. The blood levels of DHEA decline with age. DHEA is sold in the US without a prescription as a 'nutritional supplement.' It has been claimed to improve mood, boost the immune system, sharpen memory, and combat aging.