Laboratory Testing for Endocrine Abnormalities

内分泌异常要么是自我定义的疾病，要么是作为其他疾病的一部分发生的。许多历史上被认为是非内分泌的疾病越来越多地被发现与内分泌异常有关。合理使用有效的实验室测试和正确诊断内分泌疾病或非内分泌疾病的内分泌成分显然在医学和经济上都很重要。两种形式的维生素D(麦角钙化醇或D2和胆钙化醇或D3)现在都被认为是激素原。在过去的一年里，我们识别并研究了具有生物活性的25-羟基维生素D(25OH-VitD)的高效液相色谱(HPLC)测试中与药物相关的重要分析干扰，并完成了对其中一种干扰的评估。尽管带有紫外检测的高效液相色谱通常被认为是金标准，但这种方法也会受到干扰。对于25OH-VitD的定量，我们使用了最近描述的、选择性验证的高效液相色谱方法(Clin Chem 2006；52：1120-6)和Waters高效液相色谱系统。该方法使用月桂酚作为内标，能够分离和检测25OH-VitD的两种形式(D2和D3)。在18个月的时间里分析了2500多个血清样本，我们观察到8名患者的9个样本异常高(任意定义为高于运行平均值5个标准差)和通常不对称的内标峰。除一个样品外，对样品的重复测试重现了异常高和扭曲的内标峰。在一种情况下，重复得到一个分裂的内标峰：第一个峰对应于月桂酚的预期保留时间，而第二个较后的峰显然代表干扰物质。患者的用药史显示只有一种常见的药物：抗真菌药物伊曲康唑。在血清样品中加入伊曲康唑(1 mg/ml)，确实模拟了观察到的干扰，并且在内标的通常色谱位置出现了增强的高效液相色谱峰，以前证明对内标月桂酚没有干扰。由于假高的内标峰产生假低的25OH-VitD结果，并且重复测试不能消除这个问题，我们试图通过使用高效液相色谱运行的平均内标峰高或两个相邻的高效液相色谱图进行计算来纠正干扰。这两种方法给出了几乎相同的结果，通过在明尼苏达州罗切斯特市的梅奥医学实验室对样品进行LC-MS/MS(LC-MS/MS)测试，证实了这两种方法的有效性。因此，即使在没有相关用药史的情况下，本文描述的内标干扰也可以通过高效液相色谱中异常高和/或扭曲的内标峰识别，并通过我们提出的两种方法中的任何一种进行校正。

Endocrine abnormalities are either self-defined disorders or occur as part of other diseases. Many diseases that were historically considered as non-endocrine are increasingly being found to be associated with endocrine abnormalities. Optimal use of valid laboratory tests and correct diagnosis of endocrine diseases or the endocrine components of non-endocrine diseases obviously are important both medically and economically. Both forms of vitamin D (ergocalciferol or D2 and cholecalciferol or D3) are now considered prohormones. During the past year, we recognized and studied important medication-related analytical interferences with high-performance liquid chromatography (HPLC) testing for the biologically active 25-hydroxyvitamin D (25OH-vitD) and completed evaluation of one such interference. Although HPLC with UV detection generally is considered the gold standard, this methodology also is subject to interference. For 25OH-vitD quantification we are using a recently described, selective validated HPLC method (Clin Chem 2006;52:1120-6) with a Waters HPLC system. This method involves the use of laurophenone as internal standard and is able to separate and detect both forms (D2 and D3) of 25OH-vitD. Analyzing more than 2,500 serum specimens over an 18-month period, we observed unusually high (arbitrarily defined as greater than 5 standard deviations above run mean) and usually asymmetric internal standard peaks in 9 specimens of 8 patients. Except for one specimen, repeat testing of the specimens reproduced the abnormally high and distorted internal standard peaks. In one case, a split internal standard peak was obtained on repeat: the first peak corresponded to the expected retention time of laurophenone, while the second later peak apparently represented an interfering substance. Medication history of the patients revealed only one common drug: the anti-fungal itraconazole. Addition of itraconazole (1 mg/ml) to a serum specimen, previously shown to be free of interference for the internal standard laurophenone, indeed mimicked the observed interference and a heightened HPLC peak appeared at the usual chromatographic position of the internal standard. Since falsely high internal standard peaks produce falsely low 25OH-vitD results and repeat testing does not eliminate the problem, we attempted to correct the interference by using the mean internal standard peak height of the HPLC run or the two neighbouring HPLC chromatograms for calculations. The two approaches gave virtually identical results that were confirmed to be valid by testing the specimens by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) at Mayo Medical Laboratories in Rochester, MN. Thus even in the absence of relevant medication history, the internal standard interference described here can be recognized by an unusually high and/or distorted internal standard peak in the HPLC chromatogram and corrected for by either of our two proposed approaches.