TSH with Reflex to Free T4 Test
This test measures thyroid-stimulating hormone (TSH) in a blood sample. If the TSH result is abnormal, the same sample is automatically tested for free T4 as part of evaluating thyroid function.
About this test
TSH is the pituitary hormone that signals the thyroid gland to produce T3 and T4. TSH rises when thyroid hormone levels are low and falls when they are high, reflecting a feedback loop between the pituitary and the thyroid.
When the TSH result falls outside the expected range for a person's age and gender, the same serum sample is automatically tested for free T4 rather than requiring a second collection. A clinician reads TSH together with free T4, alongside clinical and family history and exam findings, since a normal TSH result excludes most cases of primary, overt thyroid disease on its own.
Test details
| Collection | Quest patient service center |
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Quest resources
Additional details
How it's often used alongside other tests
Because the reflex to free T4 happens automatically on the same sample when TSH is abnormal, this product already combines the two results a clinician typically wants when starting a thyroid function evaluation, rather than requiring a separate free T4 order.
This test isn't part of the Celio Health store at the moment, so it can't be ordered or requested here. The test menu lists everything that can.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does this test measure?
It measures TSH, and automatically tests the same sample for free T4 if the TSH result is abnormal for a person's age and gender.
How is the sample collected?
The test uses a serum sample from a routine blood draw.
Do I need to prepare for this test?
Quest lists preparation for this test related to recent fluorescein angiography and hemodialysis; preparation details appear with the test details.
Why is free T4 only sometimes reported?
The free T4 reflex runs automatically on the same sample only when the TSH result is abnormal for a person's age and gender, so a normal TSH result is reported without a separate free T4 value.
Does a normal TSH rule out thyroid disease?
A normal TSH result excludes most cases of primary, overt thyroid disease, but a clinician still reads it alongside clinical and family history and exam findings.