T4 loaded uptake - serum

Last updated: Tuesday, 30, March, 2004

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Item Process
Specimen

5 mL blood in plain tube.

Method

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

Reference Interval
Method dependent.
Application

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.

Interpretation

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

Euthyroid hyperthyroxinaemia is of no clinical significance.

Reference

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