An FLP blood test is a fasting lipid profile, a routine blood draw that measures the types and amounts of fat in your bloodstream. It checks four values: total cholesterol, LDL cholesterol (often called “bad” cholesterol), HDL cholesterol (“good” cholesterol), and triglycerides. These numbers together give a snapshot of your cardiovascular health and help determine your risk for heart disease and stroke.
What the Test Measures
Each of the four components in a fasting lipid profile tells a different part of the story. Total cholesterol is the overall amount of cholesterol circulating in your blood. LDL cholesterol is the type that builds up in artery walls and narrows them over time. HDL cholesterol works in the opposite direction, helping remove excess cholesterol from your bloodstream. Triglycerides are a type of fat your body stores for energy, and high levels are linked to increased heart disease risk.
Your results report also includes a value called non-HDL cholesterol, which is simply your total cholesterol minus your HDL. This number captures all the potentially harmful cholesterol types in a single figure.
Healthy Ranges by Age and Sex
For adults age 20 and older, the National Institutes of Health considers these levels healthy:
- Total cholesterol: less than 200 mg/dL
- LDL cholesterol: less than 100 mg/dL
- HDL cholesterol: 60 mg/dL or higher is ideal. Below 40 mg/dL in men or below 50 mg/dL in women is considered low.
- Triglycerides: below 150 mg/dL
For children and teens (age 19 and younger), the thresholds are slightly different. Total cholesterol should be under 170 mg/dL, LDL under 110 mg/dL, and HDL above 45 mg/dL.
These are general targets. Your provider may set different goals based on your age, weight, blood pressure, family history, and whether you’re already taking cholesterol-lowering medication.
Why Fasting Matters
The “fasting” part of the test exists primarily because of triglycerides. When you eat a meal containing fat, your body packages that fat into particles that enter your bloodstream, and triglyceride levels can spike at least 50% above their baseline. This surge varies widely from person to person, which makes a post-meal reading unreliable for comparison against standard reference ranges.
Fasting for 10 to 12 hours before the blood draw lets your body finish processing the fat from your last meal, so the results reflect your true baseline. During the fast, you can drink plain water but should avoid juice, coffee, soda, flavored water, and anything containing sugar or artificial sweeteners. You should also skip gum, cigarettes, and exercise during the fasting window. Ask your provider whether to continue taking any prescription or over-the-counter medications, and mention any vitamins or supplements you use.
Is Fasting Always Required?
Not necessarily. Since 2018, the American College of Cardiology and American Heart Association have accepted non-fasting lipid tests as an alternative for routine screening in people who aren’t yet on cholesterol medication. European guidelines have taken a similar position. The reasoning is that total cholesterol, LDL, and HDL are relatively stable after eating, so a non-fasting draw still gives useful information for initial risk assessment.
The exception is triglycerides. Non-fasting triglycerides at or above 175 mg/dL are considered elevated. If your non-fasting triglycerides come back above 400 mg/dL, your provider will likely order a follow-up fasting test to get an accurate baseline. So while a non-fasting draw works well for a first look, a full fasting profile may still be needed depending on the results.
How LDL Is Calculated
In most standard lipid panels, LDL cholesterol isn’t measured directly. Instead, the lab calculates it using a formula based on your total cholesterol, HDL, and triglycerides. This formula works well for most people, but it has known blind spots. When triglycerides are above 200 mg/dL, the formula tends to underestimate LDL, especially at low LDL levels. And when LDL is above 130 mg/dL, the formula tends to overestimate it.
This matters most if you’re being treated to reach a specific LDL target. If your triglycerides are high or your LDL is at an extreme end of the range, a direct LDL measurement (a different lab method that measures LDL on its own) gives more accurate results. Your provider may order this automatically, or you can ask about it if your triglycerides are elevated.
What Your Ratios Reveal
Beyond the individual numbers, the ratio between your total cholesterol and HDL cholesterol is one of the strongest predictors of cardiovascular risk. Known as the Castelli index, this ratio captures the balance between harmful and protective cholesterol in a single number. Data from large studies, including the Framingham Study, show that this ratio predicts heart disease risk more accurately than any single cholesterol value on its own.
The LDL-to-HDL ratio carries similar predictive power. What these ratios reveal is that context matters. A moderately elevated LDL paired with high HDL may pose less risk than a mildly elevated LDL paired with very low HDL. Some providers use these ratios to help decide how aggressively to treat cholesterol levels, even when LDL alone doesn’t look alarming.
When and How Often to Get Tested
The CDC recommends that most healthy adults have their cholesterol checked every 4 to 6 years. If you have heart disease, diabetes, or a family history of high cholesterol, you’ll need testing more often. Children should have at least one cholesterol check between ages 9 and 11, and again between ages 17 and 21.
An FLP is strongly recommended at any age if you have specific risk factors: a parent or grandparent who had a heart attack, stroke, or heart procedure before age 55 (for men) or 65 (for women), a parent with total cholesterol above 240 mg/dL, or if you have diabetes, high blood pressure, a BMI at or above the 95th percentile, or smoke. In these cases, guidelines recommend getting two fasting lipid profiles and averaging the results for a more reliable baseline.
What Can Skew Your Results
Several lifestyle factors can temporarily shift your lipid numbers. Alcohol consumption raises total cholesterol, LDL, and (perhaps counterintuitively) HDL. Smoking independently raises triglycerides and lowers HDL. Body fat percentage has a strong relationship with lipid levels: higher body fat correlates with higher triglycerides and higher LDL, while lowering HDL. Even your fitness level plays a small independent role, with higher cardiovascular fitness associated with modestly better triglyceride and cholesterol numbers.
For the most accurate snapshot, avoid alcohol and intense exercise for 24 hours before your blood draw, in addition to the overnight fast. If your results come back borderline or unexpected, these variables are worth discussing with your provider before making treatment decisions based on a single test.