The best blood tests for suspected iron deficiency

The best blood tests for suspected iron deficiency are ferritin, serum iron, TIBC, transferrin saturation and a CBC. Ferritin is where you start, because it measures your stored iron and drops before any of the others move.

Running one alone is the usual way to end up none the wiser. Ferritin by itself can mislead; it's what lab guidance calls a positive acute-phase reactant, meaning inflammation pushes it up even when iron is genuinely low. The transport markers by themselves mislead the other way: they show what's in circulation and nothing about what's held in reserve.

Read together, they sort each other out. Canadian lab guidance puts it precisely: a ferritin of 30 µg/L or above alongside a transferrin saturation under 20% is consistent with iron deficiency, a result that ferritin alone would have called normal.

What's in a standard iron panel

A note on naming: some labs report transferrin directly; others report TIBC. They measure the same thing. How much iron your blood can carry, so you'll see either, depending on where the work is done.

Ferritin and transferrin: what each one tells you

Ferritin stores iron. Transferrin transports it. That's the whole distinction, and it's why you want both.

• Ferritin goes down first. It's your reserve, and it empties long before anything shows in a blood count. The catch is inflammation, infection and some chronic conditions raise it independently of your iron.
• Transferrin (or TIBC) goes up as stores fall, because your body works harder to capture what's available.
• Transferrin saturation is the ratio between them. How full the carrying capacity actually is.

They move in opposite directions, which is what makes the pair useful. Low ferritin with high TIBC and low saturation is a consistent picture. A normal-looking ferritin with high TIBC and low saturation suggests something is propping the ferritin up.

Why iron alone rarely settles it

Iron shares nearly all its symptoms with zinc, vitamin D, B12 and folate. Fatigue, shedding, foggy concentration, and loss of your usual exercise capacity. All of them do it, and they overlap more often than not.

• Testing one at a time means a separate draw and a separate wait each round
• One clear result rules out one thing and leaves several
• One draw across the group narrows it in a single step

Low energy is far and away the most common reason people come to us; it led the list in our first 100 assessments, ahead of brain fog and mood changes. It's also the symptom with the longest list of possible causes.

Which panel fits your question

Basic Nutrients Iron availability (serum iron, TIBC, transferrin saturation), zinc, vitamin D, B12, folate and magnesium. The full nutrient picture in one draw, the right choice when you're working out which nutrient is behind it.

Fatigue Panel goes deeper into iron with ferritin and a CBC, and adds thyroid and blood sugar. The right choice when you've already narrowed it to iron.