Diagnostic Use
TSH is the first-line test for investigating thyroid dysfunction as it is the first to respond to change.
Increased in primary hypothyroidism. Other causes include autoimmune thyroiditis, poor compliance with thyroxine therapy, amiodarone, lithium, TSH resistance, TSH secreting pituitary adenoma or assay interference.
Decreased in primary hyperthyroidism. Other causes include non-thyroidal illness (see below), first trimester pregnancy, drugs (steroids, dopamine), thyroiditis, central hypothyroidism, isolated TSH deficiency or assay interference.
In secondary hypothyroidism due to pituitary disorders, TSH may “normal” or low, with a low free T4 .
Temporary hypothalamic/pituitary dysfunction (aka ‘sick euthyroid syndrome’) may occur with acute illness and can create a confusing thyroid function pattern. Therefore, it is generally NOT recommended to assess thyroid function when a patient is acutely unwell, unless it is believed that thyroid dysfunction is the basis of the illness.
Test Method
Principle: Electrochemiluminescence immunoassay - Sandwich principle
Analyser: Roche Diagnostics Cobas e801
Reagents: Elecsys TSH
Limitations / Interference
Interferences include TSH antibodies, heterophile antibodies and TSH molecular variants
Uncertainty of Measurement
13% at 0.07 mU/L
7.5% at >1 mU/L