The T7 Index is the product of T4 x T3 Uptake, divided by 100. it is also known as the Free Thyroxine Index.
T7= (T4 x T3-Uptake)/100
This calculation is an attempt to correct for variations in thyroxine binding proteins.
HIGH RESULTS:
T7 will usually be elevated in patients with hyperthyroidism.
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LOW RESULTS:
T7 will usually be decreased in patients with hypothyroidism. It may also be low in patients with non-thyroid illness.
Result interpretation:
| Disorder | Total T4 | T3 Uptake | T7 |
| Primary hypothyroid | Decreased | Decreased | Decreased |
| Secondary hypothyroid | Decreased | Decreased | Decreased |
| Hyperthyroid | Increased | Increased | Increased |
| T3 Toxicosis | Normal | Normal | Normal |
Reference ranges:
- males: 1.22 – 4.86
- females: 0.99 – 4.71
