T3-T4-TSH-normal-levels

T3 70 to 200 ng/dl
T4 4.5 to 13 ug/dl
TSH 0.6 to 6.0 uIU/ml

Why TSH is the best test?
TSH along with free T4 is best for Thyroid screening as the first test.
Reasons
  • TSH is more sensitive and specific for Thyroid disease than any other Thyroid parameter including Free T4
  • The TSH test is a log test sch that a 2 fold change of free T4 causes 100 fold change in TSH. Thus TSH changes far in advance of changes in free T4
  • In case of thyroid swelling TSH also helps us to decide what test is required next.
    • If TSH is less than 0.3 uIU/ml then a a Thyroid scan is necessary.
    • If TSH is more than 0.3 uIU/ml then FNAC is necessary

Is a single TSH test adequate?
A single TSH value is helpful only if TSH is extremely below or above normal.
  • Example TSH less than 0.01 uIU/ml or greater than 10 uIU/ml

If TSH is minimally abnormal we should retest TSH after
4-6 weeks.
What is the best time to measure TSH?
The best time is between 08:00 and 22:00 hours.(8 am to 10 pm)

When is Thyroid anitbodies test done?
Thyroid antibodies (anti-TPO) test should be done as part of primary screening with TSH and Free T4.

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