How Often to Retest
Test too often, test too rarely — both are waste
Retesting a stable marker every 3 months wastes money. Retesting a fast-moving marker once every 3 years misses the window to act. Each lab has a natural cadence based on how fast it moves and what you do with the result.
Annual defaults
Most labs: once per year is the right default — CBC, CMP, lipids (with ApoB), HbA1c, hsCRP, homocysteine, hormone panel, thyroid panel, vitamin D. Gives you year-over-year trend data without over-sampling.
Match marker to optimal retest frequency
Connect each lab to its right cadence.
When to retest faster
If you started therapy or a new protocol, retest the relevant marker at 3 months to confirm response — statin + ApoB, metformin + HbA1c, B-vitamin + homocysteine. If abnormal on first draw, retest in 4–6 weeks to confirm before committing to a conclusion (labs have day-to-day variability).
Lab variability — the 'true' value lives in a band
Even on the same blood draw, lab results vary ~5–10 % run-to-run for many markers and up to 30 % between morning and evening for some hormones. Standard practice for serious decisions: when a result is borderline, repeat the test 4–6 weeks later before changing therapy. Always test the same time of day, same fasted state, same lab — the trend matters far more than any single number. Tip: book your annual draw at the same time of year so seasonal variation (vitamin D, blood pressure) doesn't fool you.
Key Takeaway
Annual works for most markers. Faster if you're treating a specific abnormality or testing a new intervention. Slower or never for stable genetic markers (Lp(a)). Always confirm borderline results before acting — labs vary 5–10 % run-to-run. Calendar it — otherwise the data just doesn't get taken.