A TSH with reflex to free T4 test is one of the most efficient ways to screen for thyroid problems. It starts with a standard TSH test, and if the result is abnormal, the lab automatically measures your free T4 level without requiring a second blood draw.
What Is "Reflex to Free T4"?
"Reflex" means the lab will reflexively (automatically) run an additional test based on your TSH result. If your TSH is normal, only TSH is reported. If your TSH is high or low, the lab adds free T4 to help pinpoint whether your thyroid is truly overactive or underactive.
Why Doctors Order TSH with Reflex to FT4
- Cost-effective: You only pay for Free T4 if it's medically indicated.
- Faster diagnosis: No need to return for a second blood draw.
- Less hassle: One visit, one order, complete screening.
What Results Look Like
| TSH Result | Reflex Action |
|---|---|
| Normal | No reflex — TSH report only |
| High TSH | Free T4 added to confirm hypothyroidism |
| Low TSH | Free T4 added to confirm hyperthyroidism |
TSH with Reflex vs. Full Thyroid Panel
TSH with reflex is an excellent screening tool. However, if you have known thyroid disease, a family history, or persistent symptoms, a full thyroid panel with T3, T4, and antibodies may be more appropriate.
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