FT4 Unit Conversion: ng/dL to pmol/L
To convert FT4 from ng/dL to pmol/L, multiply by 12.87. Your initial FT4 of 1.35 ng/dL equals approximately 17.4 pmol/L, which is notably higher than your most recent measurement of 15.4 pmol/L.
Conversion Formula and Calculation
- The standard conversion factor is 12.87 (multiply ng/dL by 12.87 to get pmol/L, or divide pmol/L by 12.87 to get ng/dL)
- Your initial value: 1.35 ng/dL × 12.87 = 17.37 pmol/L
- Your recent value: 15.4 pmol/L ÷ 12.87 = 1.20 ng/dL
Clinical Context of Your Values
Your FT4 has decreased from 17.4 pmol/L to 15.4 pmol/L, representing a decline of approximately 2 pmol/L. This change warrants clinical correlation with TSH levels and symptoms 1.
Reference Range Considerations
- Normal FT4 reference ranges typically span approximately 10-23 pmol/L (0.78-1.79 ng/dL), though this varies by laboratory 2, 3
- Both your values fall within typical normal ranges, though the recent value is trending toward the lower-middle portion of the reference range 1
- Values within 2 pmol/L of reference range limits may represent normal variation rather than true thyroid dysfunction 4
Important Clinical Caveats
- Always interpret FT4 in conjunction with TSH levels - isolated FT4 values without TSH provide incomplete thyroid function assessment 1, 4
- The 2 pmol/L decrease could represent:
- Normal biological variation
- Laboratory measurement variability between different assays
- Early thyroid dysfunction requiring TSH correlation 1
- If TSH is rising while FT4 is falling, this suggests developing hypothyroidism and warrants repeat testing in 3-4 weeks 5
When to Act on Changing FT4 Values
- Monitor for hypothyroid symptoms: fatigue, weight gain, cold intolerance, constipation, hair loss 5
- Recheck thyroid function (TSH and FT4) in 3-4 weeks if symptomatic or if TSH is abnormal 5
- A falling FT4 with normal or rising TSH may indicate progression toward hypothyroidism, particularly if thyroid antibodies are positive 5