High cholesterol is diagnosed with a simple blood test called a lipid panel. Because cholesterol itself produces no symptoms in the vast majority of people, this blood test is the only reliable way to know your levels. The process is straightforward: a sample of blood is drawn, usually from your arm, and the results come back with several numbers that together paint a picture of your cardiovascular risk.
What a Lipid Panel Measures
A standard lipid panel reports five key numbers:
- Total cholesterol: the combined amount of all cholesterol in your blood.
- LDL cholesterol: often called “bad” cholesterol, this is the type that builds up inside artery walls and forms blockages over time.
- HDL cholesterol: often called “good” cholesterol, this type helps clear excess cholesterol from your arteries.
- Non-HDL cholesterol: your total cholesterol minus HDL. This captures LDL plus other harmful types of cholesterol, giving a broader view of risk.
- Triglycerides: a different type of blood fat that independently raises heart disease risk, especially in women.
Of these, LDL cholesterol gets the most attention because it’s the primary driver of plaque buildup. Your doctor will focus on this number first when deciding whether your cholesterol is high enough to warrant treatment.
The Numbers That Define “High”
LDL cholesterol is classified into five tiers, measured in milligrams per deciliter (mg/dL):
- 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
These cutoffs aren’t the whole story. An LDL of 135 mg/dL in someone who is young, doesn’t smoke, and has normal blood pressure carries a very different meaning than the same number in a 60-year-old with diabetes. That’s why the diagnosis doesn’t stop at reading a single number off the lab report.
Do You Need to Fast Before the Test?
Traditionally, you’d be told to fast for 9 to 12 hours before a lipid panel. That’s still done in many clinics, and fasting does produce the most precise LDL calculation. But guidelines from the American College of Cardiology and the American Heart Association no longer require fasting for routine cardiovascular risk screening. Non-fasting samples work well for most people, including children, older adults, people with diabetes who risk low blood sugar from skipping meals, and anyone getting an initial screening.
Fasting is still recommended in specific situations: before starting cholesterol-lowering medication, when triglycerides come back above 400 mg/dL, or when results suggest a genetic lipid disorder. If your doctor orders a fasting panel, only water is allowed during the fasting window. Coffee, juice, and even some medications can skew results.
When and How Often to Get Tested
The National Heart, Lung, and Blood Institute recommends starting cholesterol screening between ages 9 and 11, then repeating it every five years through young adulthood. Children as young as 2 should be screened if a parent or grandparent had high cholesterol, a heart attack, or a stroke at a young age.
For adults in their 20s through mid-40s, every five years is generally sufficient. The schedule tightens as you get older: men ages 45 to 65 and women ages 55 to 65 should test every one to two years. After 65, annual testing is recommended. Your doctor may test more frequently if you have diabetes, high blood pressure, a family history of heart disease, or if you’re already on cholesterol-lowering treatment.
Beyond the Basic Panel
A standard lipid panel catches most cases, but it can underestimate risk in certain people. Two additional blood tests offer a sharper picture when the standard results don’t fully explain someone’s risk.
Apolipoprotein B (apoB) measures the actual number of harmful cholesterol-carrying particles in your blood, rather than just the amount of cholesterol inside them. Think of it this way: LDL cholesterol tells you how much cargo is being shipped, while apoB tells you how many delivery trucks are on the road. More trucks means more chances for one to crash into an artery wall and start building plaque. When LDL cholesterol and apoB disagree, cardiovascular risk tracks more closely with apoB. A 2025 expert consensus from the National Lipid Association concluded that apoB adds meaningful information to a standard lipid panel and should be used alongside it when assessing risk.
Lipoprotein(a), often written as Lp(a), is a genetically determined particle that raises heart disease risk independently of LDL. Your Lp(a) level is largely set by your DNA and doesn’t change much with diet or exercise. Because it’s genetic and stable, it only needs to be measured once in your lifetime. Knowing your level helps clarify risk, particularly if you have a strong family history of heart disease that standard tests don’t fully explain.
How Overall Risk Is Calculated
A high cholesterol diagnosis doesn’t exist in isolation. Doctors plug your cholesterol numbers into a broader risk calculator to estimate your chance of having a heart attack or stroke in the next 10 years. The most widely used tool, the ASCVD Risk Estimator from the American College of Cardiology, factors in your age, sex, race, total cholesterol, HDL cholesterol, systolic blood pressure, whether you take blood pressure medication, whether you have diabetes, and whether you smoke.
For reference, the calculator defines “optimal” as a total cholesterol of 170 mg/dL, HDL of 50 mg/dL, systolic blood pressure of 110 mmHg, no diabetes, and no smoking. The further you drift from those benchmarks, the higher your estimated risk. This 10-year risk score often determines whether lifestyle changes alone are recommended or whether medication enters the conversation.
When Imaging Adds Clarity
For people whose risk falls in a gray zone, a coronary artery calcium (CAC) scan can tip the scales in one direction. This is a quick, non-invasive CT scan of your heart that detects calcium deposits in the walls of your coronary arteries. Calcium in those walls is a direct sign of plaque buildup, so a higher score means more advanced disease.
CAC testing is most useful for people between 40 and 55 with borderline risk scores, people who stopped statin therapy due to side effects and want a clearer picture of whether they need to restart, and older adults with few risk factors who are weighing whether medication is worth it. A score of zero is reassuring and may mean you can safely delay medication. A high score, even with only moderately elevated cholesterol, often shifts the decision toward treatment.
Physical Signs of Very High Cholesterol
High cholesterol is sometimes called a “silent” condition, and for the vast majority of people that’s accurate. But extremely high levels, particularly in people with familial hypercholesterolemia (an inherited form), can produce visible signs. Fatty bumps called xanthomas may appear on the elbows, knees, hands, ankles, or buttocks. Yellowish deposits can form around the eyelids. A grayish-white ring, known as corneal arcus, may appear around the colored part of the eye.
These signs are uncommon and typically indicate cholesterol levels well above 300 mg/dL, often from birth. If you notice any of them, a lipid panel will confirm the diagnosis, and genetic testing may follow to identify the specific inherited mutation.
Conditions That Push Cholesterol Up
Not all high cholesterol comes from diet and genetics alone. Several medical conditions and medications can drive cholesterol levels higher, and identifying these secondary causes is an important part of diagnosis. An underactive thyroid is one of the most common culprits. Diabetes, kidney disease (particularly nephrotic syndrome), and liver disease can all elevate cholesterol. Certain medications do the same, including some steroids, oral contraceptives, and drugs used to treat seizures or severe acne.
When cholesterol is newly elevated, your doctor may check thyroid function, blood sugar, and kidney and liver markers to rule out these underlying causes. Treating the root condition often brings cholesterol back down without the need for separate cholesterol-lowering medication.