Adjusted total thyroxine (T4-Adj), also known as free thyroxine index, is the product of total serum thyroxine (Total T4) and T3 resin uptake ratio (T3 ratio). It was measured in 93 subjects comprising 6 groups with differing thyro-metabolic states. T4-Adj was found to have a highly significant positive correlation with a conventional method for measurement of free thyroxine (free T4) in all patients studied. T4-Adj is a relatively inexpensive determination which corrects for alterations in thyroxine binding proteins and is not influenced by iodine contamination.
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Stein et al. (1972) studied this question.