Thyroid Function Tests
Last modified: 10 March 2022, 2:12:32 PM AEDT
Technique1 / 5
- TSH = Thyroid stimulating hormine
- Free thyroxine = T4
- Free T3
- Thyroperoxidase autoAb
- Thyroglobuin autoAB
Interpretation2 / 5
- TSH = 0.5-5.0 miu/L
- thyroxine replacement
- aim TSH 2 miu/L
- aim low TSH < 0.1 miu/L if history of thyroid cancer
- normal T4
- takes 6 weeks for a stable change in T4
- sick euthyroid
- normal TSH
- low T3
- hig reverse T3
Periop3 / 5
- Subclinical hypothyroidism
- High TSH, Normal T4
- Proceed
- Moderate (overt) hypothyroidism
- Elective surgery = postpone until euthyroid
- Urgent surgery = proceed
- Start on T4 1.6 mcg/kg
- Severe hypothyroidism
- Elective = postpone
- Urgent = treat ASAP
- T4 loading dose 200-300 mcg IV then 50 mcg daily
- T3 loading dose 5-20 mcg IV then 2.5 - 10 mcg/kg Q8H
Serious ill patients4 / 5
- Most inpatients have low T3
- Some 15-50% have low T4
- TSH may be low
- Previously = "euthyroid sick syndrome" "sick euthyroid"
- now, "nonthyroidal illness"