Description

Patients with non-thyroidal illnesses (NTI) may show
abnormalities in thyroid function tests even though they are
clinically euthyroid (“sick euthyroid syndrome”). As a result
of abnormalities in the hypothalamic pituitary thyroid axis,
TSH concentrations may be suppressed in the acute phase
and on recovery TSH concentrations may rise transiently
into the hypothyroid range. Total T3 and free T3
concentrations usually fall as a result of impaired hepatic
uptake of T4 and impaired conversion of T4 to T3. Illness
modifies both the concentration and binding capacity of the
plasma thyroid hormone binding proteins which diminishes
the total thyroid hormone concentrations. Free T4
concentrations usually remain within the reference range or
may be modestly raised in the sick patient, however, many
routine methods for free T4 produce low values in the sick
patient due to assay artefacts. The pattern of thyroid
function tests may mimic the profile seen in primary or
secondary thyroid disorders. Thyroid function tests should
only be requested if there is clinical evidence for suspecting a
thyroid problem. Additional investigations, repeat testing
and clinical assessment by an endocrinologist may be required
to clarify the cause of abnormal thyroid function tests in
hospitalised patients. The consensus view at present is that
T4/T3 replacement is not advocated in NTI.