Yue Bingfang, Rockwood Alan L, Sandrock Tanya, La'ulu Sonia L, Kushnir Mark M, Meikle A Wayne
ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, UT 84108-1221, USA.
Clin Chem. 2008 Apr;54(4):642-51. doi: 10.1373/clinchem.2007.098293. Epub 2008 Feb 7.
Measurements of free thyroxine (FT4) and free triiodothyronine (FT3) are important for the diagnosis and monitoring of thyroid diseases. Considerable differences among methods limit their clinical utility, however, and accurate methods are needed for various clinical specimens. We describe a direct equilibrium dialysis (ED)-liquid chromatography (LC)/tandem mass spectrometry (MS/MS) method for FT4 and FT3.
ED was selected as the separation step. Serum samples were dialyzed 1:1 against a simple protein-free buffer for 20 h at 37 degrees C. Thyroid hormones in dialysates were purified by online solid-phase extraction (SPE), then chromatographically separated and quantified in positive ion and multiple reaction monitoring modes.
For FT4 and FT3, the lower and upper limits of quantification were 1 ng/L (pg/mL) and 400 ng/L with total imprecision <10%. The method correlated well with an ED-RIA, 2 direct immunoassay methods for FT4, and 1 direct immunoassay and 1 tracer dialysis method for FT3. The adult reference intervals were 12.8-22.2 ng/L for FT4 and 3.62-6.75 ng/L for FT3. Reference intervals for the second trimester of pregnancy (14-20 weeks of gestation) were also established.
We developed a simple protein-free buffer and ED procedure. The performance characteristics and high throughput of the LC-MS/MS method with online SPE for FT4 and FT3 (also reverse T3) are sufficient for the intended clinical use.
游离甲状腺素（FT4）和游离三碘甲状腺原氨酸（FT3）的测定对于甲状腺疾病的诊断和监测至关重要。然而，不同方法之间存在显著差异，限制了它们的临床应用，因此各种临床标本需要准确的检测方法。我们描述了一种用于FT4和FT3的直接平衡透析（ED）-液相色谱（LC）/串联质谱（MS/MS）方法。
选择ED作为分离步骤。血清样本在37℃下与简单的无蛋白缓冲液按1:1进行透析20小时。透析液中的甲状腺激素通过在线固相萃取（SPE）进行纯化，然后在正离子和多反应监测模式下进行色谱分离和定量。
对于FT4和FT3，定量下限和上限分别为1 ng/L（pg/mL）和400 ng/L，总不精密度<10%。该方法与ED-RIA、两种FT4直接免疫测定方法以及一种FT3直接免疫测定方法和一种示踪剂透析方法相关性良好。成人FT4的参考区间为12.8 - 22.2 ng/L，FT3为3.62 - 6.75 ng/L。还建立了妊娠中期（妊娠14 - 20周）的参考区间。
我们开发了一种简单的无蛋白缓冲液和ED程序。用于FT4和FT3（以及反T3）的在线SPE的LC-MS/MS方法的性能特征和高通量足以满足预期的临床应用。
