Nutrients and iron markers

Why it matters: The most useful single blood test for your iron stores.

Ranges: Below 45 ng/mL points to iron deficiency when anemia is present (AGA 2020); below 15 confirms it in healthy adults (WHO 2020). Inflammation can raise ferritin.

What can affect it: Inflammation, liver disease and iron supplements.

If it’s out of range: Low iron gets a cause work-up and treatment.

When to retest: 8–12 weeks after starting iron.

Condition guide: Anemia and iron deficiency guide

Why it matters: Varies through the day; read with ferritin and binding capacity.

Ranges: Your lab's range applies.

What can affect it: Recent meals, supplements and time of day.

If it’s out of range: Read as part of iron studies.

When to retest: With iron studies.

Condition guide: Anemia and iron deficiency guide

Why it matters: Used to calculate total binding capacity and saturation.

Ranges: Your lab's range applies.

What can affect it: Iron status and pregnancy.

If it’s out of range: Part of iron studies.

When to retest: With iron studies.

Condition guide: Anemia and iron deficiency guide

Why it matters: Calculated from iron and binding capacity.

Ranges: Low values support iron deficiency; very high values prompt a check for iron overload.

What can affect it: Same as iron.

If it’s out of range: Shown, not counted.

When to retest: With iron studies.

Condition guide: Anemia and iron deficiency guide

Why it matters: Useful with vegetarian diets, long-term metformin use, numbness or large red cells.

Ranges: Below about 200 pg/mL is usually deficient; borderline results may need a follow-up test.

What can affect it: Diet, metformin, acid-reducing medicines and gut absorption.

If it’s out of range: Low levels are treated and rechecked.

When to retest: 2–3 months after treatment.

Condition guide: Vitamin deficiency test guide

Why it matters: Checked with anemia or large red cells.

Ranges: Your lab's range applies.

What can affect it: Diet, alcohol and some medicines.

If it’s out of range: Low levels are treated and rechecked.

When to retest: After treatment.

Condition guide: Vitamin deficiency test guide

Why it matters: The Endocrine Society (2024) advises against routine testing in healthy adults; we test for bone or absorption concerns.

Ranges: Many labs flag levels below 20 ng/mL.

What can affect it: Sun exposure, skin tone, weight, supplements and absorption.

If it’s out of range: Linked to DEXA bone-density decisions when appropriate.

When to retest: Rarely needed after treatment starts.

Condition guide: Vitamin deficiency test guide