Lipoproteins are particles in your blood that carry cholesterol and other fats to and from your cells. Because fats can’t dissolve in water, your body wraps them in a shell of proteins and phospholipids so they can travel through your bloodstream. When your doctor orders a lipid panel, the test measures the cholesterol carried inside different types of these lipoprotein particles.
How Lipoproteins Work
Each lipoprotein particle has the same basic design: a core of cholesterol and triglycerides (a type of fat) wrapped in an outer shell of proteins called apolipoproteins. Those outer proteins aren’t just packaging. They act as identification tags that tell your cells what to do with the particle, whether to absorb it, break it down, or send it back to the liver for disposal.
Lipoproteins handle three main jobs. They move dietary fats from your gut into the body after you eat. They shuttle fats from the liver out to tissues that need them. And they collect excess cholesterol from tissues and return it to the liver, a process called reverse cholesterol transport. The direction a lipoprotein travels, and what it’s carrying, depends on which type it is.
Types That Show Up on a Blood Test
A standard lipid panel reports numbers for LDL cholesterol, HDL cholesterol, and triglycerides, plus a total cholesterol number. Each one reflects a different lipoprotein class.
- LDL (low-density lipoprotein) carries cholesterol from the liver out to your tissues. It’s called “bad” cholesterol because when levels run high, LDL particles accumulate in artery walls. Once trapped there, they get modified and swallowed by immune cells, which triggers inflammation and builds up fatty plaque. This process, atherosclerosis, is how high LDL leads to heart attacks and strokes.
- HDL (high-density lipoprotein) works in the opposite direction, picking up excess cholesterol from tissues and ferrying it back to the liver for removal. Higher HDL levels are associated with lower cardiovascular risk.
- VLDL (very low-density lipoprotein) is produced by the liver and is the main carrier of triglycerides. Most lipid panels don’t report VLDL directly, but your triglyceride number reflects it. After VLDL delivers its triglycerides to tissues, the leftover particle shrinks and becomes an LDL particle.
There are also chylomicrons, very large lipoprotein particles your gut produces after a meal to absorb dietary fat. They clear from the blood within hours, which is why they don’t typically appear on a fasting blood test.
What the Numbers Mean
LDL cholesterol is the number doctors focus on most. The National Institutes of Health breaks it down this way:
- Below 100 mg/dL: Optimal
- 100 to 129 mg/dL: Near optimal
- 130 to 159 mg/dL: Borderline high
- 160 to 189 mg/dL: High
- 190 mg/dL and above: Very high
For HDL, higher is better. Levels below about 40 mg/dL in men or 50 mg/dL in women are generally considered a risk factor. Triglycerides below 150 mg/dL are considered normal. Your total cholesterol is the sum of cholesterol carried in all lipoprotein types combined.
Most healthy adults should have a lipid panel every four to six years, according to the CDC. People with existing heart disease, diabetes, or other risk factors typically need testing more often.
Why Fasting Matters for Accuracy
You’ve probably been told to fast before a cholesterol test. The standard instruction is to avoid all food and drinks (except water and medications) for 12 to 14 hours before the blood draw. The main reason is triglycerides: they stay elevated for several hours after eating, which throws off the results.
LDL cholesterol is usually calculated using a formula that plugs in your triglyceride level. If triglycerides are artificially high from a recent meal, the LDL number becomes unreliable. HDL and total cholesterol don’t shift much with eating, so those values hold up reasonably well in a non-fasting sample. If your doctor only needs a quick screen of total and HDL cholesterol, fasting may not be required.
Lipoprotein(a): A Separate, Often Overlooked Test
Standard lipid panels don’t measure lipoprotein(a), often written as Lp(a). This is a specialized LDL-like particle with an extra protein attached that makes it particularly good at promoting plaque buildup and blood clots. Unlike regular LDL, Lp(a) levels are almost entirely determined by your genes, not by diet or exercise.
Roughly one in five people worldwide have elevated Lp(a), defined as 125 nmol/L or above (approximately 50 mg/dL). Among people who already have cardiovascular disease, that number rises to about one in four. The risk operates on a spectrum: levels below 75 nmol/L (about 30 mg/dL) are generally considered desirable, 75 to 124 nmol/L is a gray zone, and 125 nmol/L or above is very high risk.
What makes Lp(a) tricky is that it contributes to cardiovascular risk even in people whose regular LDL cholesterol is well controlled with medication or lifestyle changes. Adding Lp(a) screening to standard risk assessment improved risk classification by nearly 40% for people in the intermediate-risk category. Since your Lp(a) level is genetically set and stays relatively stable over your lifetime, you only need to test it once. If you have a family history of early heart disease, it’s worth asking about.
Beyond LDL: Apolipoprotein B Testing
Some doctors now order a test called apolipoprotein B (ApoB). Every LDL, VLDL, and Lp(a) particle contains exactly one ApoB molecule, so measuring ApoB tells you the total number of potentially harmful particles in your blood, not just how much cholesterol they’re carrying.
This distinction matters because LDL particles come in different sizes. Small, dense LDL particles carry less cholesterol each but are considered more dangerous. A person could have a normal-looking LDL cholesterol number while actually having a large number of these small, dense particles. The standard LDL test would miss the risk; ApoB catches it. Research in people with type 2 diabetes found that ApoB predicted arterial plaque buildup while LDL cholesterol did not. In people without diabetes, both tests performed well, but ApoB still provided value beyond what LDL cholesterol alone could show.
ApoB testing is most useful for people with diabetes, insulin resistance, metabolic syndrome, or high triglycerides, all situations where standard LDL cholesterol can underestimate the true number of dangerous particles.
What Can Shift Your Results
Beyond fasting status, several factors can temporarily change lipoprotein levels. Kidney disease can markedly raise Lp(a) levels, while liver disease tends to lower them as the liver’s ability to produce lipoproteins declines. Swapping saturated fat for carbohydrates or unsaturated fats in your diet can actually increase Lp(a) by 10 to 15%, a finding that surprises many people since that dietary change lowers regular LDL. Hormone replacement therapy in postmenopausal women lowers Lp(a), with oral forms being more effective than patches.
Acute infections and inflammation can also temporarily alter lipid levels. If you’ve been sick recently or your health circumstances have changed, a single blood test may not give the full picture. Repeat testing a few weeks later can help confirm whether an abnormal result reflects your baseline or a temporary fluctuation.