Reading Your Own Bloodwork as a Supplement User: Ten Markers Worth Tracking

Standard lab reference ranges flag disease. They represent the middle 95% of the tested population, which includes many people who are not well.

If you take supplements to support health rather than treat a diagnosed problem, reading your results against those population ranges tells you whether you're sick, not whether you're doing well. That's a different question.

Here are ten markers worth tracking as a supplement user, with the standard lab range and the functional medicine target for each, and what to actually do with the number.

1. 25-OH Vitamin D

Standard normal: above 50 nmol/L (UK) / above 20 ng/mL (US)

Functional medicine target: 75 to 125 nmol/L (30 to 50 ng/mL)

Most UK adults are below 50 nmol/L in winter. Being 'not deficient' and being at a level associated with good immune, bone, and metabolic function are different things. If you are in the 50 to 75 nmol/L range and supplementing, consider increasing your dose.

The test to ask for: 25-hydroxyvitamin D (25-OH D). Available from your GP, or privately via Medichecks or Forth. Test in winter for the most useful baseline.

2. Ferritin

Standard normal: 12 to 300 mcg/L (wide variation between labs)

Functional medicine target: 50 to 100 mcg/L for women; 70 to 150 mcg/L for men

Ferritin is stored iron. Standard ranges flag deficiency below 12 to 15. Many people experience fatigue, hair loss, and brain fog at ferritin levels below 30, which labs often report as normal.

Serum iron alone is not enough. Ferritin is the more meaningful marker for your iron stores. Ask for both.

3. Serum B12 vs active B12

Standard serum B12 normal: 180 to 900 pmol/L (UK labs vary)

Active B12 (holotranscobalamin) target: above 70 pmol/L

Serum B12 measures total B12 in the blood, including forms bound to proteins that cells cannot use. A normal serum B12 doesn't rule out functional deficiency. Active B12 (holotranscobalamin) measures only what's being delivered to cells.

If you have fatigue, brain fog, or tingling and numbness alongside a normal serum B12, asking specifically for holotranscobalamin is worth doing. Private labs offer it; most NHS tests don't.

4. Folate

Standard normal: above 7 nmol/L (serum); above 340 nmol/L (red cell folate)

Functional medicine target: towards the upper half of the normal range

Folate works alongside B12 in the methylation cycle. Standard ranges were set to prevent megaloblastic anaemia, not to support optimal methylation. If you're taking methylfolate for MTHFR variants, it's worth confirming your serum or red cell folate is actually moving.

5. Zinc and copper

Standard serum zinc normal: 11 to 22 mcmol/L

What to watch: zinc-to-copper ratio, not just zinc alone

High-dose zinc supplementation (above 25 to 50 mg daily long-term) depletes copper. Copper deficiency can cause neurological problems. If you supplement with zinc, check your copper alongside it, and consider a combined zinc and copper supplement at a sensible ratio.

The functional medicine view is that a zinc-to-copper ratio of roughly 1:1 in serum is optimal. Ratios significantly above 2:1 suggest relative copper depletion.

6. RBC magnesium

Standard serum magnesium normal: 0.7 to 1.0 mmol/L

More useful test: RBC magnesium (red blood cell magnesium)

Serum magnesium is tightly regulated by the kidneys and stays 'normal' until you are quite depleted. It is not a sensitive marker for intracellular magnesium status.

RBC magnesium (magnesium inside red blood cells) better reflects actual tissue stores. If you are supplementing magnesium and want to know whether it's working, ask for RBC magnesium, not serum magnesium. Most private labs offer it; NHS rarely does.

7. Omega-3 index

Standard: no routine lab normal

Target: above 8% (high-risk cutoff is below 4%)

The omega-3 index measures EPA and DHA as a percentage of total fatty acids in red blood cell membranes. It reflects dietary and supplement intake over the past two to three months.

Most Western adults fall in the 4 to 6% range. Cardiovascular and inflammation benefits are associated with levels above 8%. If you supplement with fish oil or algae oil and want to confirm the dose is adequate, this test gives you an objective answer. Available privately; not routine on the NHS.

8. High-sensitivity CRP (hs-CRP)

Standard normal: below 10 mg/L (rules out acute infection/inflammation)

Functional medicine target: below 1 mg/L

hs-CRP is a marker of systemic inflammation. Standard ranges flag acute inflammatory events. The high-sensitivity version detects low-level chronic inflammation that standard CRP misses.

If you supplement for inflammation (omega-3, curcumin, vitamin D), a baseline hs-CRP before and after tells you whether the supplement is moving the marker. Values persistently above 2 mg/L in the absence of acute illness warrant investigation.

9. HbA1c

Standard normal: below 42 mmol/mol (6.0%) in the UK

Functional medicine target: below 38 mmol/mol (5.6%)

HbA1c reflects average blood glucose over the past two to three months. It is relevant for supplement users on metabolic routines, or taking berberine, chromium, or cinnamon extract.

Standard ranges define diabetes at 48 mmol/mol and prediabetes at 42 to 47. Functional medicine targets the lower end of normal to reduce long-term metabolic risk. If your number is creeping up through the 'normal' range, that's worth acting on regardless of whether it's crossed a clinical threshold.

10. TSH

Standard normal: 0.4 to 4.0 mIU/L (wide range)

Functional medicine target: 1.0 to 2.5 mIU/L

TSH (thyroid-stimulating hormone) is the standard first-line thyroid test. Standard ranges are wide. Many people experience fatigue, weight changes, and brain fog at TSH values that are technically 'normal' but towards the higher end.

Iodine, selenium, and zinc all support thyroid function. If you supplement these and have symptoms suggesting thyroid involvement, TSH alone is not enough. Ask for free T4 and free T3 as well to get a fuller picture.

How to ask for the right tests

Some of these (25-OH vitamin D, ferritin, B12, folate, zinc, HbA1c, TSH) are available through your GP if you describe specific symptoms or risk factors. Others (RBC magnesium, omega-3 index, active B12, hs-CRP) are more reliably obtained through private labs.

Private labs in the UK that offer most of these: Medichecks, Forth, and Thriva. A basic micronutrient panel covering D, iron, B12, folate, zinc, and copper typically runs £60 to £120. An advanced panel including RBC magnesium, omega-3 index, and hs-CRP costs more but gives a fuller picture.

Testing twice, before and after three months of supplementing, is what turns a result into useful information. A single data point tells you where you are. Two tells you whether anything changed.

How Stack Almanac helps

Stack Almanac lets you log bloodwork results alongside your supplement routine. The Almanac Advisor uses your actual numbers to personalise guidance. If your 25-OH vitamin D is 45 nmol/L and you're taking 1000 IU, it will note that the dose is unlikely to reach the functional medicine target. It works from where you are, not a generic starting point.

This is exactly the ferritin logic behind Stack Almanac's ADHD / Focus and energy protocols: iron only gets added once your own bloodwork confirms you're actually deficient.