T4 by equilibrium dialysis

Clinical use:
Measurement of serum free thyroxine when assay interference suspected in fT4 immunoassay.

Equilibrium dialysis uses a physical method to separated protein bound thyroxine from free thyroxine. The method is resilient to anti-thyroid antibodies and other immunoglobulin interferences. The method is also unaffected by most serum thyroxine binding protein abnormalities such as familial dysalbuminaemic hyperthyroxinaemia.

Patient Preparation
None. Not applicable in heparin treated patients. Please inform laboratory of any relevant medications.

Sample preparation
Transfer the blood to a plain tube. Separate the serum, preferably within 30 min of collection and store at 4°C. 500µL of serum is required.

Reference Ranges
Provided on reports. Please contact SAS laboratory.

Quality Assessment
No EQAS is available. Strict internal QC procedures are followed.

Centre offering this assay
Cambridge Addenbrooke’s Hospital Endocrine Laboratory.


Nelson JC, Tomei RT. Direct determination of free thyroxin in undiluted serum by equilibrium dialysis/ radioimmunoassay. Clin Chem. 1988 Sep;34 (9):1737-44.

Taylor KP Chatterjee VK Halsall DJ. Comparison of one-step, two-step and equilibrium dialysis methods for serum free thyroxine measurement. Ann Clin Biochem 2009 Sup 1 T55

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