T4 loaded uptake - serum

Last updated: Tuesday, 30, March, 2004

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5 mL blood in plain tube.


Radiometric assay: T3 uptake after 'loading' serum with T4.

Reference Interval
Method dependent.

The test is only performed when 'hyperthyroxinaemia' is anomalous, usually with raised total T4 and FTI but normal TSH. It identifies those with euthyroid hyperthyroxinaemia due to abnormal binding proteins eg, dysalbuminaemic hyper­thyroxinaemia.


T4 loaded uptake is abnormal if hyperthyroxinaemia is due to an abnormal plasma thyroxine-binding protein.

Euthyroid hyperthyroxinaemia is of no clinical significance.


Stockigt JR. J Clin Endo Metab 1986; 62: 230-233.