Imagine this is a thyroid function test (TFT) result that you trace from the lab information system (LIS):
– TSH 100 mIU/L (normal range 0.350 – 0.490)
– Free T4 <5.41 pmol/L (normal range 9.0 – 19.1)
What is the diagnosis based on the TFT result? [answer]

Interpretation

🔼TSH 🔽FT4: hypothyroidism
🔼TSH ↔️FT4: subclinical hypothyroidism
🔼TSH 🔼FT4: TSH secreting tumour / thyroid hormone resistance

🔽TSH 🔼FT4 or FT3: Hyperthyroidism
🔽TSH ↔️FT4: subclinical hyperthyroidism
🔽TSH 🔽FT4: central hypothyroidism (i.e. due to pituitary / hypothalamic disorders) / ‘sick euthyroid’ syndrome

↔️TSH 🔼/🔽FT4: amiodarone treatment / non-thyroidal Illness / pituitary or hypothalamic dysfunction / assay interference

Keys:
🔼: high
🔽: low
↔️: normal