How Often Should You Retest Your Blood Markers?
Retest each marker once it has had time to move: about 6 weeks for LDL and fasting glucose, 8 weeks for TSH, B12 and ALT, and 12 weeks for HbA1c, vitamin D, ferritin and hs-CRP. With nothing flagged, a yearly panel is a reasonable default for longevity tracking. FixFirst dates your retest by the slowest-moving of your top 3 priorities.
Retest timing, marker by marker
The weeks are the point at which FixFirst dates a retest. The right-hand column is why that long.
| Marker | Retest after | Why that long |
|---|---|---|
| HbA1c | 12 weeks | It reflects about 3 months of average blood sugar. |
| Fasting glucose | 6 weeks | It can respond within 4–6 weeks of consistent dietary changes. |
| Fasting insulin | 8 weeks | It can fall measurably within 2–4 weeks. Retest at 6–8 weeks, drawn fasting for 8+ hours. |
| LDL | 6 weeks | It responds to diet within 4–6 weeks. A statin's effect shows within 4 weeks. |
| Triglycerides | 8 weeks | They respond faster than cholesterol, within 6–8 weeks of consistent dietary changes. |
| HDL | 16 weeks | It changes slowly. Retest after 3–6 months of consistent aerobic exercise. |
| Vitamin D | 12 weeks | Levels typically rise meaningfully within 8–12 weeks. |
| TSH | 8 weeks | It takes 6–8 weeks to reach a new equilibrium after a dose change. |
| Vitamin B12 | 8 weeks | Levels respond quickly to supplementation, so retest in 6–8 weeks. |
| Folate | 8 weeks | It responds within 2–4 weeks of supplementation. Check B12 at the same time. |
| Homocysteine | 12 weeks | B vitamins reduce it within 4–8 weeks. Retest at 8–12 weeks. |
| Ferritin | 12 weeks | Stores take 3–6 months to rebuild. Retest at 3 months. |
| Haemoglobin | 8 weeks | It takes 6–8 weeks to rise meaningfully, because red blood cells live about 120 days. |
| eGFR | 12 weeks | KDIGO recommends repeating after 3 months to confirm a trend before classifying chronic kidney disease. |
| Creatinine | 4 weeks | It can respond in 2–4 weeks if the cause is reversible. |
| Uric acid | 8 weeks | It can drop within 2–4 weeks of dietary changes. Retest at 6–8 weeks. |
| ALT | 8 weeks | It can normalise within 4–8 weeks after the cause is removed. |
| GGT | 8 weeks | It is slow moving. It typically starts to fall within 4–8 weeks, and full normalisation in fatty liver takes 8–12 weeks. |
| hs-CRP | 12 weeks | It can respond within 2–4 weeks. Retest at 6–8 weeks for a first check and 12 weeks for a full read. |
Markers not listed default to 12 weeks in FixFirst's plan.
Your retest date follows your slowest marker
One date for the whole plan, set by whichever priority marker takes longest to respond.
Say your top 3 include low ferritin (12 weeks) and high LDL (6 weeks). FixFirst dates the retest at 12 weeks, because a ferritin retest at week 6 would still show stores that have not had time to refill. The plan states this on the page: "Set by your ferritin, the slowest to respond. Retest sooner and the numbers won't reflect the work yet."
You can still recheck LDL at 6 weeks if your doctor wants it. The 12-week date is when the whole plan can be judged.
Several priorities usually mean several supplements or diet changes. Supplements based on your blood test results shows which doses FixFirst lists and when each one is retested.
Tracking healthy markers for longevity: who sets the schedule
No guideline sets a longevity schedule for healthy adults. Here is what each source does say, and where a number is only an editorial default.
| What | How often | Who says so |
|---|---|---|
| Glucose or HbA1c, normal results | At least every 3 years, more often with risk factors | ADA Standards of Care |
| Lp(a) | Once in adulthood | 2026 ACC/AHA dyslipidemia guideline |
| Low eGFR | Repeat at 3 months | KDIGO |
| Vitamin D, glucose, ferritin, TSH, HbA1c, triglycerides, hs-CRP | Yearly | FixFirst's baseline guide. An editorial default, not a guideline |
| HbA1c, hs-CRP, free testosterone with SHBG | Every two weeks to quarterly | Tim Ferriss's own protocol (see his panel). Not a recommendation for others |
Yearly is a reasonable default if you want a baseline to compare against next year. It is a convenience, not a medical rule. If a result is flagged, switch to that marker's own clock from the table above. If a result sits just outside the range, the borderline results guide explains why a retest often beats immediate action. For HbA1c in particular, see the HbA1c guide.
Make two results comparable
A retest only tells you something if it was taken under the same conditions.
Use the same lab where you can. MedlinePlus notes that results from different labs can't be compared directly and that units can differ.
Repeat the conditions. Fast for 8 or more hours before a fasting insulin or HOMA-IR draw. Retest CRP when you are fully well. If you take creatine, stop it 2–3 weeks before a creatinine retest, as creatine raises serum creatinine.
Keep your own copy of each report. FixFirst deletes the file you upload once it has read it and does not keep your past results, so there is nothing to look back at later unless you save the PDF.
The retest reminder
If you email yourself the plan, FixFirst can nudge you when the date arrives.
When you email yourself the plan, FixFirst schedules one reminder for your retest date. To do that it keeps your email address, the retest date and the names of your priority markers. A daily job sends the reminder once the date has passed.
Only one reminder stays pending per address: a newer plan to the same email replaces an older unsent one. Every reminder has an unsubscribe link.
Where FixFirst fits in
FixFirst reads a PDF or photo of your report; you don't type values in. It scores each flagged marker on how far it sits outside the lab's range, its organ system, its long-term risk, and whether diet, activity or a supplement can move it, then adjusts for the age, sex and lifestyle answers you give, and returns your top 3 with a plan and a retest date. Dr. Prahlad Rai Gupta reviews the thresholds and plan wording FixFirst uses; no doctor looks at your report. Your doctor decides when a retest is needed for any result that is significantly out of range.
FAQ — retesting blood work
How soon can I retest after starting a supplement?
Why not retest every month?
How often should healthy adults check blood work for longevity?
Does FixFirst remind me to retest?
Should I use the same lab each time?
Do I need to fast for a retest?
References & Guidelines
Get a retest date that fits your own results
Upload your blood test report and FixFirst returns your top 3 priorities with a plan and a retest date set by the slowest-moving one.
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