Marked method differences in the measurement of thyroid function tests support the need for standardisation

Background: Thyroid function tests (TFT) are used to diagnose and monitor thyroid dysfunction disease. Though method differences recognised in the euthyroid range, variation across biochemical spectrum of disease is under-appreciated. Aim: This study compared TFT measurement euthyroid, hypothyroid hyperthyroid patients using five automated methods. Methods: TSH, free T4 T3 were measured on Roche Cobas, Abbott Architect, Siemens Atellica, Beckman DxI Ortho Vitros platforms. Method comparison was by Passing & Bablok linear regression concordance analysis performed manufacturer’s reference intervals. Results: Five-way available for 94 samples. Differences TFT, particularly T4, subtle range most marked range. specific intervals did not fully accommodate differences, leading discordance diagnosis hypothyroidism, hyperthyroidism, sub-clinical states Discussion: Correlation between methods differs dynamic For correlation closest has important implications monitoring, as can masquerade worsening or improvement Our data supports IFCC call standardisation TFT.