Dietary Restrictions Before Serum Ferritin and Transferrin Saturation Testing
Patients should avoid all iron-containing supplements and foods for at least 24 hours prior to blood draw for serum ferritin and transferrin saturation testing, with the test ideally performed in the morning. 1
Specific Pre-Test Requirements
Timing and Fasting Requirements
- Avoid all iron-containing supplements and foods for at least 24 hours before blood draw 1
- Testing should ideally be administered in the morning 1
- Fasting is not strictly required for transferrin saturation, though morning samples are preferred 2
Rationale for These Restrictions
The 24-hour avoidance period is critical because:
- Dietary iron and supplements can acutely elevate serum iron levels, which directly affects transferrin saturation calculations 1
- Transferrin saturation is calculated from serum iron divided by total iron binding capacity, making it highly susceptible to recent iron intake 1
- Accurate iron studies are essential for determining whether to use oral or intravenous iron treatment, particularly in conditions like restless legs syndrome where iron supplementation thresholds differ from the general population 1
Foods and Supplements to Avoid
Iron-Containing Items to Restrict
- All iron supplements (ferrous sulfate, ferrous gluconate, multivitamins with iron) 1
- Iron-fortified foods and cereals 1
- Red meat, organ meats (liver, kidney) 1
- Shellfish and other high-iron seafood 1
Clinical Context and Importance
Why Accurate Testing Matters
The analysis of iron studies greatly influences the decision to use oral or intravenous iron treatment, with different thresholds for supplementation depending on the clinical condition 1. For example:
- In adults with restless legs syndrome, iron supplementation should be instituted with oral or IV iron if serum ferritin ≤75 ng/mL or transferrin saturation <20% 1
- In hereditary hemochromatosis evaluation, transferrin saturation ≥45% is the key discriminator for true iron overload requiring genetic testing 2
Common Pitfalls to Avoid
- Do not check iron parameters within 4 weeks of IV iron administration, as circulating iron can interfere with assays and lead to spurious results 2
- Never use ferritin alone without transferrin saturation to diagnose iron overload, as ferritin is an acute phase reactant elevated in inflammation, liver disease, and malignancy independent of iron stores 2
- Recent iron intake can falsely elevate transferrin saturation, potentially leading to unnecessary genetic testing for hemochromatosis or inappropriate treatment decisions 1