fT4 Meaning
fT4 stands for free thyroxine 4. Thyroxine 4 is the inactive variant of thyroid hormone. In technical jargon, this is called a precursor. With fT4, the part of Thyroxine 4 that is free (unbound) in the blood is measured. This is because most of thyroid hormone is bound to various proteins. Thyroxine 4 is converted by the body, particularly in the liver, into T3, Trijodothyronine. T3 is the biologically active variant of thyroid hormone.
To determine thyroid function, it is best to measure the biomarkers TSH and T4.
fT4 Values in Men and Women: Detailed Explanation
Here is an overview of fT4 levels in men and women so you can see when your fT4 level is normal, low or high.
Normal:
An fT4 level between 13.23 and 19.95 pmol/L is considered normal. This indicates healthy thyroid function in women.
Low:
An fT4 value below 12.6 pmol/L is considered abnormal and too low. This may indicate slow thyroid function (hypothyroidism). Interpretation along with the TSH value is recommended. Values between 12.6 and 13.23 pmol/L are considered “elevated,” meaning the fT4 level is at the lower limit of normal and may require further monitoring.
High:
An fT4 level above 19.95 pmol/L falls on the high side of normal. Values between 19.95 and 21 pmol/L are considered “elevated,” indicating that the fT4 level is at the upper limit of normal. If the value exceeds 21 pmol/L, it is considered abnormal and too high and may indicate an overactive thyroid gland (hyperthyroidism). Further interpretation is then required, in conjunction with the TSH value.
Invalid:
A value of 0 pmol/L is considered invalid, possibly due to insufficient material for the test. A new measurement is recommended.
fT4 Values in Men et Woman: Detailed Explanation
| Result | Unit | Value min-max | Age | Gender | Biomarker interpretation | |
|---|---|---|---|---|---|---|
| Deviant | pmol/L | 0 - 12.6 | 18 - 20 | Man & Woman | The fT4 falls outside the normal range and is too low. Interpretation depends on the TSH. | The cause is usually an underactive thyroid gland (hyperthyroidism). |
| Caution | pmol/L | 12.6 - 13.23 | 18 - 20 | Man & Woman | The fT4 is still within the normal range, but on the low side. | Too low a fT4 may indicate a thyroid gland that works too slowly. |
| Normal | pmol/L | 13.23 - 19.95 | 18 - 20 | Man & Woman | The fT4 is good. | |
| Caution | pmol/L | 19.95 - 21 | 18 - 20 | Man & Woman | The fT4 is still within the normal range, but on the high side. | An excessively high fT4 may indicate a thyroid gland that is working too fast. |
| Deviant | pmol/L | 21 - 100 | 18 - 20 | Man & Woman | The fT4 falls outside the normal range and is too high. Interpretation depends on the TSH. | The cause is usually a thyroid gland working too fast (hyperthyroidism). |
| Deviant | pmol/L | 0 - 11.6 | 20 - 100 | Man & Woman | The fT4 falls outside the normal range and is too low. Interpretation depends on the TSH. | The cause is usually a thyroid gland working too slowly (hyperthyroidism). |
| Caution | pmol/L | 11.6 - 12.18 | 20 - 100 | Man & Woman | The fT4 is still within the normal range, but on the low side. | Too low a fT4 may indicate a thyroid gland that works too slowly. |
| Normal | pmol/L | 12.18 - 20.81 | 20 - 100 | Man & Woman | The fT4 is good. | |
| Caution | pmol/L | 20.81 - 21.9 | 20 - 100 | Man & Woman | The fT4 is still within the normal range, but on the high side. | An excessively high fT4 may indicate a thyroid gland that is working too fast. |
| Deviant | pmol/L | 21.9 - 100 | 20 - 100 | Man & Woman | The fT4 falls outside the normal range and is too high. Interpretation depends on the TSH. | The cause is usually a thyroid gland working too fast (hyperthyroidism). |
