Can taking biotin (Vitamin B7) affect the accuracy of iron level tests?

Biotin Interference with Iron Testing

Biotin does not directly interfere with standard iron tests (serum iron, ferritin, transferrin saturation, or TIBC), but it can cause false results in certain immunoassays that use biotin-streptavidin technology—iron studies typically do not use this methodology and are therefore not affected. 1

Understanding Biotin Interference Mechanism

Biotin interference occurs specifically in immunoassays that utilize biotin-streptavidin binding technology. 2 The direction of interference depends on the assay design:

• Sandwich immunoassays: Biotin causes falsely decreased results 3, 4
• Competitive immunoassays: Biotin causes falsely increased results 3, 4

Iron Tests and Biotin Interference

Standard iron studies are not susceptible to biotin interference because they do not rely on biotin-streptavidin technology:

• Serum ferritin: Measured by immunoassay but typically not affected by biotin in most platforms 1
• Serum iron: Measured by direct chemical analysis, not immunoassay 2
• Total iron-binding capacity (TIBC): Measured by direct chemical analysis 2
• Transferrin saturation: Calculated from serum iron and TIBC, both unaffected by biotin 2

However, one research study found ferritin may show false elevation with biotin on certain platforms, though this is not consistently reported across all assay systems. 4

Tests That ARE Affected by Biotin

Be aware that biotin does interfere with these commonly ordered tests:

• Cardiac markers: High-sensitivity troponin T (falsely decreased) 2, 3
• Thyroid function: TSH (falsely decreased), free T4 and free T3 (falsely increased) 4, 5
• Hormones: FSH, LH (falsely decreased); testosterone, estradiol, progesterone (falsely increased) 3, 4
• Other markers: Vitamin D (falsely increased), PTH, pro-BNP 2, 4

Clinical Recommendations

When ordering iron studies in patients taking biotin:

• Standard iron panels (ferritin, serum iron, TIBC, transferrin saturation) can be ordered without concern for biotin interference 1
• If using hemoglobin/hematocrit for anemia screening, these are not affected by biotin as they are direct measurements 1
• Discontinue biotin supplementation 48-72 hours before testing if ordering hormone or cardiac panels that use biotin-streptavidin technology 4

Critical Pitfall to Avoid

The FDA warns that biotin levels higher than the recommended daily allowance may cause interference with cardiovascular diagnostic tests (e.g., troponin) and hormone tests, leading to incorrect results. 6 Always ask patients about over-the-counter biotin supplements, as doses of 10 mg/day or higher commonly cause clinically significant interference. 5

Practical Algorithm

1. Ask every patient: "Are you taking biotin supplements?" 6
2. If yes and ordering iron studies only: Proceed without delay—no interference expected 1
3. If yes and ordering thyroid, cardiac, or hormone panels: Instruct patient to stop biotin for 48-72 hours before blood draw 4
4. If biotin cannot be stopped (e.g., high-dose therapy for multiple sclerosis): Use alternative testing methods not based on biotin-streptavidin chemistry, or interpret results with extreme caution 4
5. If unexpected results occur: Consider biotin interference and retest after biotin washout period 3, 4