Free T3:Free T4 Ratio
The Free T3:Free T4 ratio reflects the conversion of T4 to the active T3 hormone. A low ratio may suggest poor T4 to T3 conversion.
Category: Thyroid Panel
Also known as: free t3 : free t4
Reference range: 2–4.5 ratio (Source: ABIM)
Standard unit: ratio
High values may indicate
A high ratio may indicate excessive T3 production or hyperthyroidism.
Low values may indicate
A low ratio may suggest poor conversion of T4 to T3, possibly indicating selenium deficiency or thyroid dysfunction.
Frequently asked questions
- What is a normal Free T3:Free T4 Ratio level?
- A typical reference range for Free T3:Free T4 Ratio is 2–4.5 ratio (source: ABIM). Reference ranges vary by laboratory, age, and sex, so always compare against the range on your own lab report.
- What units is Free T3:Free T4 Ratio measured in?
- Free T3:Free T4 Ratio is most commonly reported in ratio. Labs in different countries may use other units — you can convert between them with BloodId's blood test unit converter.
- Where do Free T3:Free T4 Ratio reference ranges come from?
- BloodId uses ABIM standard reference ranges and educational information from MedlinePlus (see our methodology). Reference ranges still vary by lab, age, and sex, so always compare against your own report.
- Can I track Free T3:Free T4 Ratio over time?
- Yes. Upload results from any lab and BloodId charts your Free T3:Free T4 Ratio over time against its reference range, so you can see whether the trend is rising, falling, or stable.
Related biomarkers
Source: BloodId admin-reviewed
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