Did it really go down?

What your stamp means

1. Can't tell yet: the change is inside normal test-to-test noise. Keep going and test again in 6 to 12 weeks.
2. Probably real: for LDL that's a change of 19% or more. One more test confirms it.
3. Real change: 29% or more for LDL. Something moved, so look at what you changed in the weeks before.

A clean retest, once

1. Same lab as last time, since labs differ a little.
2. Same fasting state: fasted both times or fed both times. A meal moves triglycerides up to about 26 points.
3. The right gap: 4 weeks for triglycerides, 6 to 12 for LDL.
4. Write down the date and anything unusual that week, like a cold or a big weekend.

How it works

Your numbers move from week to week with nothing changed, and every lab test adds a little error of its own. Together they set how big a change has to be before it's likely real: about 12% for total cholesterol, 15% for HDL, 19% for LDL and 42% for triglycerides at the 80% line, and 19%, 23%, 29% and 64% at the 95% line.

Those bands come from within-person variation across 30 studies (Smith 1993) and the most imprecision CDC allows a certified lab, so a good lab's real bands are a little narrower. If one draw was after a meal and the other wasn't, the meal's share comes out first: triglycerides about 26 up, total and LDL about 8 down, HDL about 4 down. The guideline checks a panel 4 to 12 weeks after a change.