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Thyroid Function Panel (with Free T4 and TSH)

Published: August 9, 2026Updated: August 16, 2026

This test measures key thyroid hormones to assess your thyroid health, including thyroid-stimulating hormone (TSH) and free thyroxine (T4).

Quick summary

["Your thyroid hormones help regulate metabolism, energy, and overall health—this test helps check if they’re working properly."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
38031-1
Short code
Deprecated US Thyroid Bx needle guide
Synonyms
Deprecated US Thyroid Bx needle guide
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us
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 Is Done

Doctors may order this panel to diagnose or monitor thyroid disorders, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It can also be used during pregnancy, before surgery, or if you have symptoms like fatigue, weight changes, or unexplained mood swings.

What to Expect Before the Test

No special preparation is needed for most thyroid tests. If you’re taking thyroid medication, your doctor may ask you to stop temporarily or adjust timing. Blood is drawn from a vein in your arm, similar to other blood tests.

What the Results Mean

TSH measures how well your pituitary gland signals your thyroid to produce hormones. Free T4 reflects the active form of thyroxine circulating in your blood. Abnormal results may indicate thyroid imbalances that need medical attention.

Common Symptoms to Watch For

Symptoms like unexplained weight changes, fatigue, hair loss, or changes in heart rate can signal thyroid issues. If you experience these, discuss them with your doctor—this test may help identify the cause.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Frequently asked questions

What does a thyroid function panel help detect?
This panel helps diagnose conditions like hypothyroidism (low thyroid hormone levels), hyperthyroidism (high hormone levels), or subclinical thyroid dysfunction. It’s also useful for monitoring treatment progress if you’re on thyroid medication.
How often should I get this test?
Your doctor will determine how often you need retests based on your health status, symptoms, and treatment plan. Some patients may need annual checks, while others may need more frequent monitoring.
Can I eat or drink before this test?
Most thyroid tests don’t require fasting, but if your doctor specifies otherwise (e.g., for certain thyroid antibodies), follow their instructions. Avoid caffeine or alcohol before blood draw if advised.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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