3,5-Diiodotyrosine excretion in human urine in individuals of differing thyroidal status

The urinary excretion of 3,5-diiodotyrosine was determined in euthyroid, hypothyroid and hyperthyroid individuals using a sensitive gas chromatographic mass spectrometric assay. This involved a multi-step extraction of the amino acid from urine (mean efficiency 28 +/- 5.7%) then conversion to the N,O-diheptafluorobutyryl methyl ester. The fragmentation of the derivative is discussed. Although the mean excretions in the two pathological states were significantly different from that of euthyroid individuals (P less than 0.01 in both instances) there was considerable overlap with the normal range.