OBJECTIVES Thyroid dysfunction is a common medical condition affecting an estimated 30 million people in the US alone. Employing gold standard Liquid chromatography-tandem mass spectrometry (LC-MSMS) methods we have examined the extent of inaccuracy of immunoassay (IA) measurement for total T3 (TT3) at low, normal and high concentrations. DESIGN AND METHODS 268 TT3 Roche Cobas 6000 immunoassay TT3 values (covering the low, normal, and high ranges) were compared with LC-MSMS results. RESULTS At TT3 concentrations between 50 and 113ng/dL (conversion factor for TT3 to SI Units is ng/dL×0.0154=nmol/L), n=122, LC-MSMS values were lower than immunoassay with 72% found to be below the 2.5th percentile by LC-MSMS compared to 27% for immunoassay. Strikingly 45% of the patients classified as normal TT3 by immunoassay were defined as lower than the 2.5th percentile by LC-MSMS. Only 38 of the 122 patients with low T3's were not receiving T4. In this latter group all of whom had TSH's>3.7mIU/L, 74% of results by LC-MSMS were below the 2.5th percentile while only 21% were below the 2.5th percentile by IA. The clinical consequences of these inaccuracies may affect whether dosing with T4 or combination of T4 with T3 is selected for treatment. Finally the correlation of TT3 with TSH was far superior when TT3 was measured by LC-MSMS. A typical case which demonstrates our message is included. CONCLUSION T3 being the active hormone needs to be reliably measured and if the patient has low TT3 and hypothyroid symptoms persist; treatment with T3 should be considered. A typical case report is included to illustrate the problems of inaccurate immunoassay results for TT3. Measurement of TT3 by immunoassay at low concentrations is less than optimal and often provides the clinician with a normal result when the LC-MSMS method and the patient's clinical condition suggests that supplementation with T3 (as in combination therapy) may be required to optimize patient care.

中文翻译：

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在低浓度下通过免疫测定测量TT3是否可靠？罗氏Cobas 6000与LC-MSMS的比较。

目的甲状腺功能障碍是一种常见的医学疾病，仅在美国就估计有3000万人受到影响。我们使用金标准液相色谱-串联质谱（LC-MSMS）方法检查了低，正常和高浓度下总T3（TT3）免疫测定（IA）测量的不准确程度。设计与方法268 TT3 Roche Cobas 6000免疫测定TT3值（包括低，正常和高范围）与LC-MSMS结果进行了比较。结果在TT3浓度在50到113ng / dL之间（TT3到SI单位的转换因子为ng / dL×0.0154 = nmol / L），n = 122时，LC-MSMS值低于免疫分析，发现72％低于LC-MSMS检测结果为2.5％，而免疫检测结果为27％。令人惊讶的是，通过免疫测定被分类为正常TT3的患者中有45％被定义为低于2。LC-MSMS排名第五。122例T3低的患者中只有38例没有接受T4。在后一组中，所有患者的TSH均> 3.7mIU / L，LC-MSMS结果的74％低于2.5％，而IA仅为21％低于2.5％。这些不准确的临床后果可能会影响是否选择使用T4剂量或T4与T3的组合进行治疗。最终，当通过LC-MSMS测量TT3时，TT3与TSH的相关性要好得多。其中包括一个典型的案例来说明我们的信息。结论T3是一种活性激素，需要进行可靠的测定，并且如果患者的TT3较低且甲状腺功能减退症状持续存在，则应予以确定。应该考虑用T3治疗。其中包括一个典型病例报告，以说明TT3免疫测定结果不准确的问题。