LDL vs HDL vs triglycerides: what a lipid panel actually measures

Every standard lipid panel prints four numbers and a ratio or two. Here's what each one physically measures, why they're grouped together, and what the flags next to them mean.

What a lipid panel is

A lipid panel measures the fats circulating in your blood at the moment of the draw. Cholesterol itself doesn't dissolve in blood — it travels packaged inside particles called lipoproteins, and the panel is really counting the cholesterol carried by each kind of particle. That's why the results are named after carriers (LDL, HDL) rather than the cholesterol molecule itself.

Most labs report the same four measurements, in the same order. Some add calculated values — a ratio, non-HDL cholesterol, or an estimated LDL — which are derived from the four measured numbers rather than measured separately.

How it looks on the printed report

Labs print each result with a unit (usually mg/dL in the US, mmol/L elsewhere), a reference interval, and sometimes a flag — H or L — when the value falls outside it. A typical block looks like this:

An anonymized example. "CALC" means the LDL value was calculated from the other three, not measured directly.

Why the same panel differs between labs

Two labs can report slightly different values and different reference intervals for the same blood — equipment, calibration and the population the lab used to define "normal" all vary. That's why a trend built from one lab is cleaner than points scattered across labs, and why the lab name belongs next to every reading you keep.

The ratios at the bottom

Many reports end with derived values: total/HDL ratio, non-HDL cholesterol, sometimes VLDL. None of these are new measurements — they're arithmetic on the four numbers above, printed as a convenience. If your report doesn't show them, nothing was left out of the test.