The differential diagnosis of a low serum total thyroxine (T4) includes a low serum thyroxine binding globulin (thyroid binding globulin).
Clinical and laboratory features:
(1) The patient has a low serum total T4 (thyroxine).
(2) The serum TSH is normal.
(3) The patient has no signs of hypothyroidism.
(4) The serum free thyroxine is normal.
Problems that may arise:
(1) The patient is misdiagnosed as hypothyroidism and started on increasing doses of thyroxine.
(2) The patient is clinically hyperthyroid but has a normal serum thyroxine.
(3) Misdiagnosis of congenital hypothyroidism.
Conditions associated with low serum thyroxine binding globulin:
(1) congenital thyroxine-binding globulin deficiency
(2) hypoproteinemia (nephrotic syndrome, end-stage cirrhosis)
(3) drugs
(4) intensive care
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Specialty: Clinical Laboratory, Obstetrics & Gynecology, Cardiology, Emergency Medicine, Critical Care
