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Thyroid Stimulating Hormone (TSH)

Thyroid Function

5 minutesBlood draw

A blood test that measures TSH, the hormone that regulates thyroid function.

Duration
5 minutes
Sample Type
Blood draw ()
Results Timeline
1-2 business days
Morning draw may be more consistent

How to Prepare

Follow these instructions to ensure accurate test results

No fasting needed
You can eat normally before this test
Morning preferred
TSH levels are highest in early morning
Medication timing
If on thyroid medication, ask your doctor about timing
Things to Avoid
  • •Biotin supplements 2-3 days before (can interfere with results)

Day of Your Test

  • Schedule for the same time of day if retesting (for consistency)
  • If taking thyroid medication, take it after the test
  • Bring list of all current medications and supplements

What This Measures

To screen for thyroid disorders including hypothyroidism (underactive) and hyperthyroidism (overactive thyroid).

  • •TSH hormone level produced by pituitary gland
  • •How well your thyroid is responding to brain signals
  • •Overall thyroid function status

Why This Test Matters

Thyroid hormones affect metabolism, energy, weight, mood, and many body functions. Untreated thyroid disorders can cause fatigue, weight changes, heart problems, and other symptoms.

Normal Ranges

Normal Range
Varies slightly by lab
0.4 - 4.0 µIU/mL
Optimal Range
Many feel best in this range
1.0 - 2.5 µIU/mL
High TSH
May indicate hypothyroidism
Above 4.0
Low TSH
May indicate hyperthyroidism
Below 0.4

Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.

After the Test

  • No restrictions - resume all normal activities
  • Take thyroid medication if you skipped it before the test
  • Minor bruising at needle site is normal

Understanding Results

If High

High TSH usually means hypothyroidism (underactive thyroid). Symptoms may include fatigue, weight gain, cold sensitivity. Treatment is typically thyroid hormone replacement.

If Low

Low TSH usually means hyperthyroidism (overactive thyroid). Symptoms may include weight loss, anxiety, rapid heartbeat. Treatment depends on the cause.

Good to Know

  • TSH naturally fluctuates throughout the day
  • Stress, illness, and pregnancy can affect levels
  • Many factors including age affect what's "normal" for you
  • If you have symptoms but normal TSH, discuss with your doctor

Follow Up

  • •Discuss results with your doctor within 1-2 weeks
  • •If starting thyroid medication: retest in 6-8 weeks
  • •If stable on medication: retest every 6-12 months
  • •Additional tests (T3, T4, antibodies) may be needed if abnormal

Source: Test preparation information is based on standard clinical guidelines and laboratory best practices. This information is provided for reference purposes only and should not replace professional medical advice, diagnosis, or treatment. Always follow the specific instructions provided by your healthcare provider or laboratory.