To the Editor.—
In our clinic it has become routine to obtain radioimmunoassay (RIA) serum thyroid stimulating hormone (TSH) measurements in every thyroid profile ordered. Thus, with the serum thyroxine (T4), triiodothyronine (T3), T3 percent uptake, free T4 and cholesterol, a measurement of TSH is ordered. In these clinical data it has been found frequently that an abnormal TSH level above 7.5 μU/ml was present, even when the serum T4 level was within accepted normal range, (7.5 to 15 μg/dl). When this was true, there was good evidence of subclinical hypothyroidism: serum cholesterol level above 300 mg creatine phosphokinase (CPK) level above 50 units, occasional high lactic acid dehydrogenase (LDH) level, characteristic ECG changes, slow achilles reflex relaxation time, increased left ventricular ejection time (LVET), delayed ventricular relaxation time, and prolonged preejection period (PEP).1,2Thus, if the physician was depending on the RIA serum T
Starr P. Diagnostic Value of Thyroid Stimulating Hormone. JAMA. 1977;238(22):2367. doi:10.1001/jama.1977.03280230031011
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