“Free Thyroxine Index”: A Reliable Substitute for “Free” Thyroxine Concentration
Open Access
- 1 January 1974
- journal article
- research article
- Published by Oxford University Press (OUP) in American Journal of Clinical Pathology
- Vol. 61 (1) , 118-121
- https://doi.org/10.1093/ajcp/61.1.118
Abstract
“Free thyroxine index,” determined as the product of thyroxine-I (T4-I) by competitive protein-binding and T3 uptake of 125I-triiodothyronine by surface adsorption on inorganic silicate particles, is compared with “free” thyroxine concentration. The normal range of index resulting from use of the Tri-Tab T3 uptake method is 0.9-2.9, and coincides very well with that for “free” thyroxine (1.0-2.3 ng. per dl.). Eighty-nine of 102 specimens (87.2%) showed agreement between the two. The coefficient of correlation (r) is 0.929, and the linear regression equation is y = 1.01x + 0.15. Of the 13 specimens that did not show agreement, three missed by only 0.1 unit of index.Keywords
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