Comparison of FT4 with log TSH on the Abbott Architect ci8200: Pediatric reference intervals for free thyroxine and thyroid-stimulating hormone

Abstract

Background We evaluated the clinical validity of serum FT4 measurements by assessing its correlation with log TSH. To provide pediatric reference intervals (representative ranges) for FT4, and TSH on the Architect ci8200 integrated system. Methods This population-based study encompassed 6023 children (3369 females and 2654 males). The percentile and Hoffmann approaches for obtaining reference intervals on these analytes were also compared. Results FT4 correlation with log TSH was poor ( r = 0.010 for males and 0.050 for females). Reference intervals were established. TSH and FT4 did not show a significant sex difference; moreover, the intervals decreased with age for FT4 and TSH. Conclusions Whereas in a previous study ultrafiltration tandem mass spectrometry yielded a correlation of r = 0.90 for FT4 vs. log TSH this present study reveals a poor FT4 vs. log TSH correlation in the pediatric population studied and indicates the FT4 immunoassay conducted on the Abbott Architect ci8200 is less useful clinically than might have been expected. Reference intervals using the Hoffmann approach for pediatric in- and out-patients compare well with previously published results utilizing the percentile approach.