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Evaluation of Elecsys free triiodothyronine assay: relevance of age-related reference ranges
R Sapin1, J L Schlienger, B Goichot
1Laboratoire Universitaire de Biophysique, CNRS URA 1173, Faculté de Médecine, Strasbourg, France. sapin@alsace.u-strasbg.fr
Objective:
This study aimed at evaluating Elecsys free triiodothyronine (FT3) assay performed on an Elecsys 2010 system, while paying special attention to age relationship in euthyroid subjects.
Design And Methods:
FT3 levels were measured in 149 euthyroid control subjects aged between 2 and 92 years old, 33 hyperthyroid and particular euthyroid patients: female in the last 3 months of pregnancy (n = 30), nonthyroidal ill hospitalized in medical (NTlm, n = 31), or intensive care units (NTlc, n = 31) and amiodarone-treated (n = 27).
Results:
FT3 was inversely related to age in controls (r = -0.67). Three reference ranges were used: below 20 years 4.5-9.0 pmol/L, between 20 and 60 years 3.9-7.2, and over 60 years 2.4-6.5. Compared to age-matched controls, FT3 decreased in pregnancy, NTlm, NTlc, and amiodarone groups. Use of age-related reference ranges improved the specificity markedly in amiodarone patients and to a lesser extent in NTlm and TClc patients.
Conclusions:
The reliability of the Elecsys FT3 assay was found to be satisfactory for clinical use, when the age of patients was taken into account.