Every marker
Iron
The iron circulating in your blood right now, on its way to the tissues that use it. It moves through the day and with what you last ate.
Ferritin
How much iron your body has in storage, the reserve it draws on between meals and through a heavy period.
Transferrin
The protein that carries iron around your bloodstream. Your body makes more of it when iron is scarce.
Transferrin saturation
What proportion of your iron carriers are actually loaded. It is the best single read of whether iron is reaching the places that need it.
Total iron binding capacity (TIBC)
How much iron your blood could carry if every carrier site were filled. It is the same information as transferrin, expressed differently.
Vitamin B12
The fraction of your B12 that is bound to the carrier your cells can actually take up. Roughly a fifth of the total, and the part that matters.
Folate
Folate circulating in your blood, which tracks what you have eaten over the last few days more than what your body has banked.
Vitamin D
The circulating store of vitamin D your body draws on, built from sunlight on skin and from what you eat or supplement.
Magnesium
The small fraction of your body's magnesium that circulates in blood. Your kidneys hold this number steady, so it tells you less than people assume.
