1. Iron stores and the role of blood tests

Iron is needed to make hemoglobin, and iron deficiency can occur before anemia develops. Symptoms such as fatigue alone cannot establish iron deficiency or iron-deficiency anemia. The American Society of Hematology (ASH) patient guide says evaluation should include a complete blood count (CBC), with ferritin, serum iron, total iron-binding capacity, or transferrin testing considered as appropriate. Anemia and depleted iron stores are related but not interchangeable findings, so results need to be interpreted together.

2. Ferritin thresholds depend on population and purpose

The World Health Organization (WHO) 2020 guideline lists ferritin below 15 µg/L as an indicator of iron deficiency in apparently healthy adults. For adults with infection or inflammation, it says ferritin below 70 µg/L may indicate iron deficiency; this is a conditional recommendation based on low-certainty evidence. Inflammation, infection, liver disease, and obesity can raise ferritin and obscure depleted stores, so neither value is a universal cutoff for every clinical setting.

The ASH 2026 diagnostic guideline and its official visual summary address adults excluding menstruating or pregnant individuals, menstruating individuals and pregnant individuals separately, using a baseline ferritin threshold of 30 ng/mL or lower. Additional circumstances can support use of a threshold of 50 ng/mL or lower. For non-menstruating, non-pregnant adults it includes iron-deficiency-related signs or symptoms or ongoing risk factors. For menstruating individuals it includes heavy menstrual bleeding or other abnormal uterine bleeding with excessive loss, associated symptoms, additional risk factors, upcoming surgery or pregnancy planning. For pregnant individuals with anemia, 50 ng/mL or lower may be appropriate with or without additional risk factors or associated symptoms. Read the population-specific recommendations with their remarks rather than treating 50 as a universal threshold.

For adults with inflammation, ASH suggests evaluating both ferritin and transferrin saturation (TSAT) rather than ferritin alone. Iron deficiency may be considered when ferritin is below 100 ng/mL or TSAT is below 20%. Measuring both is different from requiring both results to be below their thresholds. WHO 2020 and ASH 2026 have different populations and purposes; local clinicians need to interpret these findings with the history and other blood tests.

3. Assess inflammation and the reason for iron loss

Ferritin reflects iron stores but can rise during inflammation, so a normal or high result does not always rule out deficiency. WHO advises considering infection or inflammation when interpreting ferritin and notes that other iron markers may be useful. ASH also describes serum iron, total iron-binding capacity, transferrin, and TSAT as tests a clinician may order. Once deficiency is identified, evaluation of possible causes—such as menstrual blood loss, pregnancy, diet, gastrointestinal disease, or bleeding—depends on the person’s history and findings. Taking supplements indefinitely without assessing the cause can delay recognition of an underlying problem.

4. Record equivalent units without merging different criteria

Ferritin at 1 µg/L equals 1 ng/mL. Converting units does not make thresholds for different populations and inflammatory states interchangeable. Record “date / ferritin, units and laboratory reference range / hemoglobin and CBC / whether TSAT and inflammation markers are available / recent illness, bleeding and medicines / clinical interpretation and next test.”

A fictional entry, “ferritin 40 ng/mL, CBC and inflammatory status not yet reviewed,” cannot establish either absence of deficiency or a need for supplements. Obtain the original report and ask which context informs interpretation. Do not fill unmeasured TSAT or inflammation markers with “normal.”

5. Iron salt weight differs from elemental iron

ASH advises checking elemental iron on the package, distinguishing it from iron salt content and showing the product to the clinician. A fictional label says “iron salt 325 mg / elemental iron 65 mg per tablet.” Copy these as distinct items rather than recording 325 mg as elemental iron. The example is not a conversion rule for all products or a suggested dose.

Absorption and tolerability also need review. ASH discusses antacids, tea/coffee and high-calcium foods in relation to iron absorption. Bring product names, other medicines, timing with meals and adverse symptoms to a clinician or pharmacist to confirm the plan. Dose, interval, duration and repeat testing depend on the cause and circumstances; do not increase the dose yourself because it is poorly tolerated or a result has not changed as expected.

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