THE SERUM TYROSINE LEVEL AS AN INDEX OF THYROID FUNCTION

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Abstract
SUMMARY: Serum tyrosine was measured in 22 normal subjects, 17 patients with non-toxic goitre, ten patients with hypothyroidism, 37 patients with thyrotoxicosis and eight geriatric patients. Low values were obtained in hypothyroidism and high values in thyrotoxicosis. In thyrotoxicosis there was only a small overlap with the euthyroid subjects. Thus, measurements of serum tyrosine appear to be a useful test for the diagnosis of hyperthyroidism, not invalidated by previous iodine administration and not involving the use of radio-isotopes. Administration of vitamin C reduced the increased values of tyrosine in thyrotoxicosis to normal levels. It is suggested that a latent vitamin C deficiency may partly explain the increase in the serum tyrosine values in thyrotoxicosis.