Ferritin test: what it measures and how to prepare

In the absence of inflammation, blood ferritin is positively correlated with total body iron stores: low in iron deficiency and high in iron overload [2]. That link was shown in the first serum ferritin assays [3] [4].

Compared with bone marrow iron, the old reference standard, ferritin was by far the most powerful blood test for iron deficiency anemia [1]. Low ferritin is highly specific for iron deficiency, while high ferritin is non-specific [5]. The hub guide covers the biology.

Ferritin reflects stores built over weeks to months, so a single meal does not meaningfully change it. Serum iron is different: it moves with recent iron intake, so labs sometimes ask for a morning, fasting sample when a full iron panel is ordered. Ask the lab or clinician which applies.

Things that matter more than fasting:

• Recent illness. Infection and inflammation raise ferritin. WHO recommends measuring CRP alongside ferritin where inflammation is common [2].
• Hard training. Intense exercise raises hepcidin and affects iron markers [6]; avoid testing right after a race or very hard session.
• Iron supplements. Tell the clinician if you take them, and when you last took a dose.
• Recent blood donation. Ferritin can stay low for months after a donation [7].

• Hemoglobin (CBC): shows whether iron deficiency has progressed to anemia.
• Transferrin saturation: the share of transferrin carrying iron. Below 20% supports iron deficiency in inflammation [8]; above 45% in women or 50% in men suggests overload [5].
• Serum iron and TIBC: used to calculate transferrin saturation.
• CRP: a raised CRP means ferritin may overstate stores [2]. See hs-CRP.

According to one clinical review, no single test is diagnostic unless ferritin is low, or transferrin saturation is low with a raised TIBC [9]. The ferritin vs iron page explains how each one differs.

Groups with high rates of low ferritin include:

• menstruating and pregnant people [10] [11]
• regular blood donors: most donors without iron supplements had not rebuilt stores 168 days after one donation [7]
• endurance athletes, with deficiency in about 15% to 35% of female athlete cohorts [6]
• people with gut conditions that impair absorption, such as coeliac disease [12]

Ferritin with transferrin saturation is also the first step in checking for hemochromatosis when there is a family history or unexplained liver enzyme changes [13].

The fatigue trial authors suggested assessing blood markers after six weeks of treatment [14]. During hemochromatosis treatment, ferritin is checked regularly against targets of below 50 µg/L during induction and below 100 µg/L for maintenance [13].

Ferritin can move quickly after a bleed, a donation or an infection, so a single unexpected result is worth repeating before acting on it. Tracking ferritin over time, alongside hemoglobin and CRP, shows the trend more clearly than one value.

This guide does not list prices because they change often and differ by country, insurer and lab. When comparing options, check that the test reports ferritin in ng/mL or µg/L with the lab's reference range, and consider adding transferrin saturation and CRP, since ferritin alone can mislead [2].

At-home finger-prick kits measure ferritin from a small blood sample. Results should be discussed with a clinician, especially if they are low, since low ferritin needs a cause.