Tests before supplements: four numbers instead of a medicine cabinet
One lab test and one blood draw cost less than a bottle of multivitamins and tell you more than a month of reading forums. Four tests answer almost all questions about supplements using the method. How to take them, which reference ranges to consider practical, and what to do with the numbers — below. Section — what you need and what you don’t.
Four tests
| Test | What it shows | Practical range | What to do if out of range |
|---|---|---|---|
| 25(OH)D | vitamin D stores | 30-50 ng/mL (75-125 nmol/L) | below 20 — dose prescribed by a doctor; 20-30 — 2000 IU and retest in 3 months |
| Ferritin | iron stores | 30-100 µg/L; for hair and energy 50+ | below 30 — look for the cause, supplements as prescribed by a doctor |
| B12 | vitamin B12 stores | above 400 pg/mL; 200-400 — gray zone | homocysteine for clarification; supplement when taking metformin or omeprazole, and after 50 |
| TSH | thyroid gland | 0,4-4,0 mU/L | above 4 — free T4, antibodies, endocrinologist |
How to take the tests
In the morning, fasting, and outside an acute illness — a cold raises ferritin and distorts the picture. Not during your period for ferritin. If you are already taking vitamin D, do not stop: the test will show your working level. Biotin in supplements distorts TSH — stop it three days beforehand. Take all four with one blood draw, usually in one tube. Three months after starting supplementation, retest whatever was below the normal range.
Why blood magnesium is not tested
99% of magnesium is inside cells and in bones; in the blood, it is one percent, and the body keeps it stable until the very end. Blood will show a normal level even with an obvious deficiency. Assessment is based on symptoms — cramps, sleep, cravings for sweets — and diet. There is a red blood cell magnesium test; it is more accurate but rarely needed: it is easier to take 300-400 mg for two weeks and observe the symptoms. Details — magnesium.
What to test depending on the situation
Fasting insulin and glucose — if your weight has stalled and you crave sweets: insulin resistance. Omega-3 index — if you are unsure about your fish intake; target 8% and above. If vitamin D deficiency is suspected, it is supplemented with calcium and parathyroid hormone testing, but that is already a matter for a doctor. Complete blood count — once a year as a baseline. Everything else — as prescribed, not out of curiosity: unnecessary tests lead to unnecessary supplements.
Action plan
Take four tests
After a month on the method, once your diet has stabilized and electrolytes have evened out.
Compare it with the practical range, not the laboratory range
The lab writes “normal from 10” for ferritin — this is not about health, but about the absence of anemia.
One supplement for one deficiency
At the practical dose. Not a multivitamin.
Retest after 3 months
Only what was below the normal range. If it has increased — maintenance dose. If not — see a doctor.
Frequently asked questions
The doctor says ferritin 12 is normal.
According to the laboratory range — yes. Based on how you feel, your hair, and your training — no. Discuss a target of 50 and look for the cause of the losses.
Do I need to take tests if nothing is bothering me?
25(OH)D in winter — yes, deficiency can be asymptomatic. Everything else — if there are symptoms or once a year as a baseline.
How much does it cost?
Four tests at a private lab cost less than a month of multivitamins and a “fat burner.” And they are the only money here that definitely has not been wasted.
- What You Need and What You Don’t
- Vitamins and Minerals
- Electrolytes and Hydration
Reviewed by Anastasia Zhukova, Fitness Trainer • Author of a Nutrition and Training System • Creator of an AI Personal Support Platform
A human has reviewed this material against the method and real client practice.