Serum thyroglobulin stability for immunoassay

Background: Serum thyroglobulin (Tg) measurements may be affected by preanalytical factors, such as sample handling and processing, which is not quite clear at present. Methods: The authors measured Tg in sera left on the clot (4 degrees C), or timely pipetted off the clot (RT), or= subjected to 5 cycles of freezing (-80 degrees C, 3 months at cycle 4 and 24 h at the other cycles) and thawing (RT 1,h). Result: Sample storage for,4 to 24 h yielded Tg concentrations of 102.4 % to 104.5% (P=0.484) for unseparated, and 98.4 %: to 102.1% (P=0.202) for timely separated sera relative to baseline samples (1 h). Freezing-thawing resulted in significant decreases in Tg concentrations (P < 0.001) by mean 30.7% after the last cycle, with the greatest single cycle decrease by mean 18.1 % at cycle 4. Conclusion: Thyroglobulin. is stable for at least 24 h in unseparated sera at 4 C or separated sera at room temperature, but not in sera undergoing even a short period of frozen storage.