Stability of serum thyroid hormones following 8-11 years of cold storage

Ethnic differences necessitate a need for local reference intervals (RI), but establishing these can be challenging in some cultures that are reluctant to donate blood. Frozen sera are an alternative, but results can be questionable. Between 1998 and 2001, we collected blood samples from 343 healthy pregnant Chinese women (5-41 weeks' gestation), and in 2001 published gestational RI for thyrotropin thyroid stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3) using the ACS180, now obsolete. As a pilot to re-establishing RI, TSH, FT4 and FT3 were re-assayed in archived specimens using contemporary assays.

Thirty archived specimens (-80 degrees C) with ACS180 TSH concentrations ranging from 0.25 to 3.7 mIU/L were measured using the Roche E170, Advia Centaur and Architect i2000 TSH, FT4 and FT3 assays, along with 10 newer contemporary samples. Results were compared to the original, and examined in context of past and present methodological performances in an external quality assurance (EQA) program.

All contemporary assays detected significantly lower TSH and increased FT4 and FT3 concentrations in the stored samples.

With reference to methodological performances in EQA, the results obtained with contemporary assays suggest analyte deterioration in specimens and thus their unsuitability for re-establishing RI.