Lipkowski M, Dibbelt L, Seyfarth M
Institute for Clinical Chemistry, Medical University of Luebeck, D 23538 Luebeck, Germany.
Clin Biochem. 2000 Nov;33(8):635-41. doi: 10.1016/s0009-9120(00)00189-2.
Carbohydrate-deficient transferrin CDT has originally been defined as the sum of isotransferrins exhibiting isoelectric point values > or = 5.7 asialo, monosialo, and disialo transferrin but may also include at least in part trisialo transferrin when measured by modern commercial immunoassays. To examine the effects of divergently defining the analyte CDT, we compared two commercial assays yielding differently composed CDT fractions with a high-performance liquid chromatography HPLC assay commonly regarded as a reference method of CDT determination.
Relative CDT levels (CDT concentrations expressed as percent of total transferrin) were determined in 142 sera by (i) a turbidimetric immunoassay (ChronAlco I.D.) reportedly detecting asialo to disialo transferrin as CDT, (ii) an analogous assay (CDT Turbidimetric ImmunoAssay [TIA]) said to additionally include part of trisialo transferrin into the CDT fraction measured, and (iii) an anion-exchange HPLC method. Isotransferrins separated by the two commercial assays were also investigated by isoelectric focusing.
Data from HPLC and isoelectric focusing indicate that the ChronAlco assay detects major parts of asialo, monosialo, and disialo transferrin as CDT while the CDT TIA yields CDT as the total of asialo, monosialo, disialo, and trisialo transferrin. When relative CDT concentrations obtained by both assays were classified as either normal or elevated according to reference ranges cited by the manufacturer and then were compared to analogously classified HPLC data, there were clearly more discrepancies between corresponding results from CDT TIA and HPLC (22%) than between ChronAlco and HPLC results (9%).
Including trisialo transferrin into the CDT fraction enlarges the analytical signal and therefore slightly improves assay precision but also results in a significant number of pathologic results in samples exhibiting physiologic levels of the classical CDT components asialo to disialo transferrin. As long as the diagnostic information of the trisialo transferrin concentration is largely unknown, we strongly recommend not to include this isotransferrin into the determination of CDT.
碳水化合物缺乏转铁蛋白（CDT）最初被定义为等电点值≥5.7的去唾液酸转铁蛋白、单唾液酸转铁蛋白和双唾液酸转铁蛋白等同种转铁蛋白的总和，但通过现代商业免疫测定法测量时，至少部分三唾液酸转铁蛋白也可能包含在内。为了研究对分析物CDT进行不同定义的影响，我们将两种产生不同组成的CDT组分的商业检测方法与通常被视为CDT测定参考方法的高效液相色谱（HPLC）检测方法进行了比较。
通过以下方法测定了142份血清中的相对CDT水平（CDT浓度以总转铁蛋白的百分比表示）：（i）一种比浊免疫测定法（ChronAlco I.D.），据报道该方法将去唾液酸至双唾液酸转铁蛋白检测为CDT；（ii）一种类似的检测方法（CDT比浊免疫测定法[TIA]），据说该方法还将部分三唾液酸转铁蛋白纳入所测量的CDT组分中；（iii）一种阴离子交换HPLC方法。还通过等电聚焦研究了两种商业检测方法分离出的同种转铁蛋白。
HPLC和等电聚焦的数据表明，ChronAlco检测法将去唾液酸转铁蛋白、单唾液酸转铁蛋白和双唾液酸转铁蛋白的主要部分检测为CDT，而CDT TIA产生的CDT为去唾液酸转铁蛋白、单唾液酸转铁蛋白、双唾液酸转铁蛋白和三唾液酸转铁蛋白的总和。当根据制造商引用的参考范围将两种检测方法获得的相对CDT浓度分类为正常或升高，然后将其与类似分类的HPLC数据进行比较时，CDT TIA与HPLC的相应结果之间的差异（22%）明显多于ChronAlco与HPLC结果之间的差异（9%）。
将三唾液酸转铁蛋白纳入CDT组分中会扩大分析信号，因此略微提高了检测精度，但也会导致大量样本出现病理结果，这些样本中经典CDT组分去唾液酸至双唾液酸转铁蛋白的水平处于生理水平。只要三唾液酸转铁蛋白浓度的诊断信息在很大程度上未知，我们强烈建议在CDT测定中不要纳入这种同种转铁蛋白。
