Ferritin is the single most useful blood test for hair loss.

The single most useful blood test for hair loss is ferritin (iron stores), distinct from the iron currently circulating in blood (which is what serum iron and haemoglobin measure).

Standard labs flag ferritin below 15–30 ng/mL as low. Hair specialists target above 50 ng/mL; some target above 70 for active hair loss.

A “normal” ferritin of 35 may be too low for hair, even if it’s within the standard reference range. Low ferritin can prolong telogen effluvium and worsen female pattern hair loss. If you’re shedding and your ferritin came back “normal but on the low side,” it’s worth a conversation with your doctor about treating to a higher target.