The short answer
Book a morning slot, fast overnight, stop supplements for 4 to 7 days and wait until you have been well for 3 to 4 days. Ask for ferritin, iron, transferrin and saturation together, plus a blood count and CRP.
The five rules
- 1Book a morning slot, before 9 am, and keep the same time next time.
- 2Fast overnight. Water is fine and helps. Save coffee for after.
- 3Stop supplements 4 days before, a week if you can. This matters most for iron, B vitamins and biotin. Keep taking medicines your doctor prescribed.
- 4Skip alcohol and hard training the day before.
- 5Test when you are well and not on your period. Wait until you have been well for 3 to 4 days. A sore tooth or a cold sore counts.
What to ask for
| Test | Why |
|---|---|
| Complete blood count, with MCV | Haemoglobin and the size of your red cells |
| Ferritin | Your iron stores |
| Serum iron, transferrin and saturation | Iron in transport, from the same draw |
| CRP | Whether inflammation is pushing ferritin up |
| Total protein and albumin | The building material for ferritin and transferrin |
| 25-OH vitamin D and TSH | Two loops that can keep iron low |
| B12 and folate | If you eat little meat, or your red cells are large |
Use the same lab every time, so your trend is clean.
Combine iron, ferritin and transferrin from different days or labs.
Ferritin is measured with antibody tests that vary between labs. Two labs a week apart can disagree a lot, so compare results within one lab.
A real page from The Iron GuideEvery marker on one card, with a lab range and a goal.See more pagesQuestions
Do I need to fast for a ferritin test?
Ferritin itself changes little with a meal, but the serum iron and saturation on the same panel do. Fasting overnight keeps the whole panel readable.
How long before a blood test should I stop iron?
At least 4 days is a common rule and a week is better, unless your doctor says otherwise. Never stop a prescribed medicine on your own.
Can I test during my period?
It is better not to. Wait until your period has finished and you have been well for a few days, so the panel shows your usual state.
Sources
- 1.NIH Office of Dietary Supplements. Iron: fact sheet for health professionals
- 2.World Health Organization. Guideline on use of ferritin concentrations to assess iron status in individuals and populations, 2020
- 3.The Iron Guide, part 3: Your numbers
This page has not been reviewed by a clinician yet. Read it as general education, and take your own results to your doctor.
Educational, not medical advice. ferritin.ai does not diagnose or treat any condition, and it never sets a dose. Talk to your doctor about your own results.