Laboratory Testing for Endocrine Abnormalities

内分泌异常是自我定义的疾病或作为其他疾病的一部分发生。许多过去被认为是非内分泌疾病的疾病越来越多地被发现与内分泌异常有关。有效的实验室检查的最佳使用和内分泌疾病或非内分泌疾病的内分泌成分的正确诊断显然在医学和经济上都是重要的。维生素D的两种形式（麦角钙化醇或D2和胆钙化醇或D3）现在被认为是激素原。在过去的一年中，我们认识到并研究了重要的药物相关的分析干扰与高效液相色谱法（HPLC）检测的生物活性25-羟基维生素D（25 OH-vitD），并完成了这样的干扰的评价。虽然HPLC和UV检测通常被认为是金标准，但该方法也会受到干扰。对于25 OH-vitD定量，我们使用最近描述的、选择性验证的HPLC方法（Clin Chem 2006;52：1120-6）和沃茨HPLC系统。该方法涉及使用月桂苯作为内标，并且能够分离和检测25 OH-vitD的两种形式（D2和D3）。在18个月的时间内分析了超过2，500份血清标本，我们在8名患者的9份标本中观察到异常高（任意定义为高于运行平均值5个标准差）且通常不对称的内标峰。除一份样本外，样本的重复检测重现了异常高且扭曲的内标峰。在一种情况下，重复获得分裂的内标物峰：第一个峰对应于月桂酚酮的预期保留时间，而第二个较晚的峰显然代表干扰物质。患者的用药史仅显示一种常见药物：抗真菌药伊曲康唑。向血清样品中加入伊曲康唑（1 mg/ml），先前显示不干扰内标物月桂酰苯，实际上模拟了观察到的干扰，并且在内标物的通常色谱位置出现了升高的HPLC峰。由于假性高内标物峰产生假性低25 OH-vitD结果，重复检测并不能消除该问题，因此我们尝试通过使用HPLC运行的平均内标物峰高或两个相邻HPLC色谱图进行计算来校正干扰。这两种方法得到了几乎相同的结果，通过在罗切斯特，MN的马约医学实验室采用液相色谱-质谱/质谱（LC-MS/MS）检测标本，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，本文所述的内标物干扰也可以通过HPLC色谱图中异常高和/或失真的内标物峰识别，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.