Serum thyroid hormone concentrations fall
in thyroxine-treated patients during acute nonthyroidal illness
(November 2004)
The background of the study. Serum thyroxine (T4)
concentrations fall during nonthyroidal illness in some patients,
a change that could indicate a decrease in T4 secretion, a decrease
in serum protein binding of T4, or an increase in uptake of T4 into
tissue. Serum T4 and other thyroid hormones and thyrotropin (TSH)
were measured repeatedly during a nonthyroidal illness and after
recovery in patients with hypothyroidism who were treated with T4.
How the study was done. The study subjects were
six men with hypothyroidism taking 0.1 to 0.15 mg of T4 daily who
had an acute illness and were hospitalized on an intensive-care
unit. All had normal serum T4, triiodothyronine (T3), and thyrotropin
(TSH) concentrations before the onset of their illness. They were
given their usual dose of T4 while hospitalized. Serum total T4,
total T3, and TSH were measured at the time of admission (day 1);
on days 3, 5, and 7; and 7 days after discharge.
The results of the study. The average serum T4
and T3 concentrations were lower on day 1 than at the time of pre-illness
testing (Table). The values were even lower on day 3, and then gradually
increased. The average serum TSH concentration was lower on day
1 than at the time of pre-illness testing, decreased further on
day 3, then increased to above both the pre- and post-illness values
on day 7.
The conclusions of the study. Serum T4 and T3
concentrations fall transiently during acute illness in patients
with hypothyroidism being treated with T4. Since the patients were
taking T4, the changes were probably due to decreased serum protein
binding of T3 and T3.
The original article. Wadwekar D, Kabadi UM. Thyroid
hormone indices during illness in six hypothyroid subjects rendered
euthyroid with levothyroxine therapy. Exp Clin Endocrinol Diabetes
2004;112:373-7.
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