From the Guidelines
Patients should stop taking iron supplements for at least 24 hours before getting blood work to establish a baseline iron level, as this allows for the most accurate representation of the body's true iron status. This recommendation is based on the most recent and highest quality study, which suggests that testing should ideally be administered in the morning, avoiding all iron-containing supplements and foods at least 24 hours prior to blood draw 1. The waiting period of 24 hours is sufficient to diminish the temporary effects of supplemental iron on blood tests, providing a more accurate representation of the body's true iron status.
Key Considerations
- Iron supplements can cause short-term spikes in serum iron levels that don't reflect the body's actual iron stores.
- If you're taking prescription iron supplements for diagnosed iron deficiency anemia, consult your healthcare provider before stopping, as they may want to see your levels while on treatment.
- When scheduling your blood test, it's also best to have it drawn in the morning and while fasting, as iron levels naturally fluctuate throughout the day and can be affected by recent food intake.
Clinical Implications
- The decision to use oral or intravenous (IV) iron treatment is greatly influenced by the analysis of iron studies, making it essential to establish an accurate baseline iron level.
- Consensus guidelines suggest that supplementation of iron in adults with certain conditions should be instituted with oral or IV iron if serum ferritin ≤ 75 ng/mL or transferrin saturation < 20% 1.
Summary of Evidence
- A study published in the Journal of Clinical Sleep Medicine in 2025 provides the most recent and highest quality evidence for this recommendation 1.
- An older study published in Kidney International Supplements in 2008 also discusses the assessment of iron status, but its recommendations are less relevant to the current question 1.
From the FDA Drug Label
Serum iron determinations (especially by colorimetric assays) may not be meaningful for 3 weeks following the administration of iron dextran. The patient should stop taking iron supplements for at least 3 weeks before getting blood work to establish a baseline iron level 2.
From the Research
Stopping Iron Supplements Before Blood Work
To establish a baseline iron level, it is essential to stop taking iron supplements for a certain period before getting blood work. The duration of this period is not explicitly stated in the provided studies, but we can look at the absorption and bioavailability of iron from different supplements:
- Iron absorption from supplements is greater with alternate day than with consecutive day dosing in iron-deficient anemic women 3
- The bioavailability of iron from different supplements varies, with some having higher bioavailability than others 4, 5, 6, 7
Factors Affecting Iron Levels
Several factors can affect iron levels, including:
- The type of iron supplement taken 4, 5, 6, 7
- The dosing schedule of the supplement 3
- The individual's iron status and absorption rate 3, 6, 7
Recommendations
While there is no direct answer to the question of how long to stop taking iron supplements before blood work, we can consider the following:
- Iron absorption and bioavailability can vary depending on the supplement and individual factors
- Stopping iron supplements for at least 24 hours may be necessary to allow for the acute hepcidin increase to decrease and to get a more accurate baseline iron level 3
- However, the optimal duration for stopping iron supplements before blood work is not clearly established and may depend on individual circumstances and the specific supplement being taken.