Thyroid Stimulating Hormone (TSH) with Free Thyroxine (FT4) Ratio
This test measures your thyroid-stimulating hormone (TSH) and evaluates how your thyroid hormone levels are functioning together to regulate your metabolism.
["Assesses thyroid function by linking TSH and free thyroxine (FT4) for balanced metabolic health."]
Key facts at a glance
- LOINC
- 29316-7
- Short code
- TSH 30M p chal SerPl-aCnc
- Synonyms
- TSH 30M p chal SerPl-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 0.4
- Ref high
- 4
- Critical range
- 0.1 N/A – 20 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 84443
- SNOMED
- 301343003
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Matters
Your thyroid gland produces hormones that control many important functions in your body, such as metabolism, energy levels, and mood. This test helps doctors check if your thyroid is working properly by examining the relationship between TSH and FT4. TSH is a hormone from your pituitary gland that signals the thyroid to produce more or less thyroid hormone. FT4 is the active form of thyroxine, the main thyroid hormone in your blood. Together, they provide a clearer picture of whether your thyroid is underactive (hypothyroidism), overactive (hyperthyroidism), or functioning normally.
What to Expect Before the Test
No special preparation is needed for this test. You may have a blood sample drawn from a vein in your arm, similar to other blood tests. If you are on thyroid medication, let your healthcare provider know before the test, as it may affect your results.
What the Results Mean
Results are interpreted as a ratio of TSH to FT4. A normal ratio suggests balanced thyroid function, while an abnormal ratio may indicate thyroid dysfunction. Your healthcare provider will discuss the results with you and may recommend further testing if needed.
Common Causes of Abnormal Results
Abnormal TSH-FT4 ratios can be caused by conditions such as thyroid nodules, autoimmune thyroid disease (like Hashimoto’s or Graves’ disease), thyroid cancer, or other hormonal imbalances. This test helps identify these issues early, allowing for timely treatment.
Reference range
Adult: 0.4-4.0 mIU/LN/A
Take your thyroid medication after the blood draw if applicable. No fasting required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
TSH-FT4 Ratio Test
Frequently asked questions
How often should I get this test?
Can I eat or drink before this test?
What are the typical symptoms of thyroid issues that might lead to this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy