Performance characteristics of six third-generation assays for thyroid-stimulating hormone.

Background: Thyroid-stimulating hormone (TSH) is used to detect primary hypo- and hyperthyroidism. Current guidelines for TSH assays recommend a functional sensitivity of < or =0.02 mIU/L. The protocol for determining the functional sensitivity of TSH assays specifies analyses of serum samples with two reagent lots over a 6- to 8-week period.

Methods: We determined the functional sensitivities of the Access 2, ADVIA Centaur, ARCHITECT i2000, E170, IMMULITE 2000, and Vitros ECi automated methods, using seven serum pools and two reagent lots for each method.

Results: The observed functional sensitivities were as follows: Access 2, <0.020 mIU/L; ADVIA Centaur, 0.039 mIU/L; ARCHITECT i2000, <0.005 mIU/L; Elecsys E170, 0.011 mIU/L; IMMULITE 2000, 0.014 mIU/L; Vitros ECi, 0.004 mIU/L. However, there were large differences between some method means for the seven serum pools. For the pool with the lowest TSH concentration, mean results were as follows: Access 2, 0.0203 mIU/L; ADVIA Centaur, 0.0085 mIU/L; ARCHITECT i2000, 0.0049 mIU/L; E170, 0.0098 mIU/L; IMMULITE 2000, 0.0077 mIU/L; Vitros ECi, 0.0014 mIU/L. Method-comparison studies using samples with TSH concentrations >0.2 mIU/L also showed method differences. The ARCHITECT i2000 method was the most precise at low TSH concentrations.

Conclusions: TSH methods do not provide comparable results for serum pools with TSH concentrations <0.2 mIU/L or for patient results across the analytic measurement range. Further investigation into the cause of these differences and additional harmonization efforts are required.