Why did my cholesterol go up when I didn't change anything?
It may not have, really. Two LDL results can differ by about 19% by chance, and now and then by 29%, with nothing changed. Real causes include menopause, fast weight loss, keto, an underactive thyroid and some medicines. Retest at the same lab before you worry.
What we’d do
Before you blame your diet, check three things: the same lab, the same fasting state and the same LDL formula. Then retest in 4 to 12 weeks at that lab. If it’s still up by more than the noise below, take the list of causes on this page to your doctor.
How big a jump can be noise
Your cholesterol isn’t a fixed number. It drifts from week to week, and the lab adds a little error of its own. Across 30 studies, a person’s LDL varied about 9.5% between tests on average, and CDC lets a certified lab add up to 4% more. Put together, this is how big a change has to be before it’s probably real, and before it’s very likely real.
| Number | Probably real from | Very likely real from | At a typical value |
|---|---|---|---|
| Total cholesterol | 12% | 19% | at 220, 27 and 41 points |
| LDL | 19% | 29% | at 130, 24 and 37 points |
| HDL | 15% | 23% | at 50, 8 and 12 points |
| Triglycerides | 42% | 64% | at 150, 63 and 96 points |
It’s like a bathroom scale. Your weight bounces a pound or two from day to day, and a cholesterol result bounces more.
Three ways the test itself moves
- Fasting one time and not the other. A normal meal lowers LDL by up to about 8 points and raises triglycerides by up to about 26. Fasting for the second test can make LDL look 8 points higher.
- A different LDL formula. Most LDL is calculated, and labs use different formulas. At triglycerides of 240, two common ones can be 5 points apart (see why does my report say my LDL is calculated?).
- A different lab. Certified labs can each be off by a few percent in opposite directions.
Real causes of a higher LDL
The 2026 guideline lists these, beyond genes:
- Food and weight: more saturated fat, trans fat or cholesterol, weight gain, rapid weight loss, and ketosis from a keto diet
- Health conditions: an underactive thyroid, kidney disease, liver disease that blocks the flow of bile, diabetes, Cushing syndrome and anorexia
- Medicines: high-dose water pills, steroids, estrogens, androgens, some antipsychotics and cyclosporine
- Life stages: pregnancy and the menopause transition
The menopause jump is the one people miss. In a study that followed 1,054 women every year, LDL and ApoB rose sharply in the year before and the year after the last period, more than age alone explained (why does cholesterol go up after menopause?). Age itself adds a little too, since LDL climbs about 1 to 2 points a year in young adulthood.
If you started a new medicine around the time your numbers rose, don’t stop it on your own. Ask the person who prescribed it. Did it really go down? works the same way for a rise, and tells you whether the change is bigger than the noise.
6 sources
- Smith SJ, Cooper GR, Myers GL and Sampson EJ, Biological variability in concentrations of serum lipids, Clinical Chemistry, 1993pubmed.ncbi.nlm.nih.gov
- CDC Clinical Standardization Programs, certification criteria for cholesterol test manufacturerscdc.gov
- Langsted A, Freiberg JJ and Nordestgaard BG, Fasting and nonfasting lipid levels: influence of normal food intake on lipids, lipoproteins, apolipoproteins, and cardiovascular risk prediction, Circulation, 2008pubmed.ncbi.nlm.nih.gov
- Blumenthal RS, Morris PB, Gaudino M and others, 2026 ACC/AHA guideline on the management of dyslipidemia, JACC, 2026doi.org
- The same guideline, full text, Circulation, 2026api.iscpcardio.org
- Matthews KA and others, Are changes in cardiovascular disease risk factors in midlife women due to chronological aging or to the menopausal transition?, Journal of the American College of Cardiology, 2009pubmed.ncbi.nlm.nih.gov
