Interpretation Of TFT's

Question 1

T3 or T4

Answer 1

T4 is better to measure, specifically T4

Produced in a ratio of 20:1 respectively and 99% of T4 is bound to TBG

Half life is 1 week so have to wait several weeks before repeating TFTS to see a change

Question 2

Primary hyperthyroidism

Answer 2

Excessive production of T3/4 from the gland due to an intrinsic glandular problem

Raised T3/4
Low TSH

Causes;
Graves
TMG
Toxic adenoma

Question 3

Secondary hyperthyroidism

Answer 3

Stimulation of the thyroid gland caused by excessive TSH

Raised TSH
Raised T3/4

Causes;
TSH secreting tumour

Question 4

Primary hypothyroidism

Answer 4

Reduced secretion of thyroid hormone due to an intrinsic glandular problem

Raised TSH
Low T3/4

NB- normal T4 and raised TSH can suggest sub clinical hypothyroidism (underlying autoimmune disease)

Causes;
Hashimoto’s thyroiditis 
Thyroidectomy 
De Quervains thyroiditis 
Radioactive iodine treatment 
Amiodarone

Question 5

Secondary hypothyroidism

Answer 5

Reduction in hormones that stimulate the thyroid gland to produce thyroxine

Low T3/4
Low TSH

Causes;
Pituitary adenoma (non-functioning)
Brain surgery/ radiotherapy (pituitary or hypothalamus)
Hypothalamic tumour

NB- TRH (hypothalamus) isn’t measured on a blood test as not much in the circulation. Linked with TSH in the secondary causes