Thyroid hormone reference intervals in an ambulatory Arab population on the Abbott Architect i2000 immunoassay...

Considerable differences in reference intervals for FT4 and TSH have been reported between countries. Method related differences in the distribution of free thyroxine (FT4) have also been reported. The aim of this study was to establish reference intervals for thyrotrophin (TSH) and FT4 in an ambulatory adult (16-75 y) Arab population attending a general practice clinic using the Abbott Architect i2000 immunoassay analyzer.

TSH and FT4 results from 959 consecutive ambulatory Arab subjects were available. After excluding data sets from pregnant women, patients with known and newly diagnosed thyroid disease, individuals taking medication that may affect TSH and FT4 and individuals with acute illness, 742 data sets were available for analysis. A 2-way between-groups ANOVA was conducted to explore the impact of age and gender on TSH and FT4.

TSH showed a non-Gaussian distribution, FT4 showed a near normal distribution. There was no significant main effect on FT4 and TSH for age and gender. The interaction effect of age and gender also did not reach significance. The 95% reference intervals were: TSH 0.30-4.32 mU/l and FT4 9.8-18.6 pmol/l. The reference intervals for TSH and FT4 determined in this study differed from those reported from other countries using the same analytical platform and from the 99% reference intervals, provided by the manufacturer.

These differences in reference intervals in different populations may affect patient management. The data reported reemphasize that each laboratory should determine population and method-specific reference intervals.