Toward standardization of carbohydrate-deficient transferrin (CDT) measurements: II. Performance of a laboratory network running the HPLC candidate reference measurement procedure and evaluation of a candidate reference material

Abstract

Carbohydrate-deficient transferrin (CDT) is a descriptive term used for a temporary change in the transferrin glycosylation profile caused by alcohol, and used as a biomarker of chronic high alcohol consumption. The use of an array of methods for measurement of CDT in various absolute or relative amounts, and sometimes covering different transferrin glycoforms, has complicated the comparability of results and caused confusion among medical staff. This situation prompted initiation of an IFCC Working Group on CDT standardization. This second publication of the WG-CDT covers the establishment of a network of reference laboratories running a high-performance liquid chromatography (HPLC) candidate reference measurement procedure, and evaluation of candidate secondary reference materials. The network laboratories demonstrated good and reproducible performance and thus can be used to assign target values for calibrators and controls. A candidate secondary reference material based on native human serum lyophilized with a cryo-/lyoprotectant to prevent protein denaturation was found to be commutable and stable during storage. A proposed strategy for calibration of different CDT methods is also presented. In an external quality assurance study involving 66 laboratories and covering the current routine CDT assays (HPLC, capillary electrophoresis and immunoassay), recalculation of observed results based on the nominal values for the candidate calibrator reduced the overall coefficient of variation from 18.9% to 5.5%. The logistics for distribution of reference materials and review of results were found to be functional, indicating that a full reference system for CDT may soon be available.

Toward standardization of carbohydrate-deficient transferrin (CDT) measurements: III. Performance of native serum and serum spiked with disialotransferrin proves that harmonization of CDT assays is possible

“…All samples were distributed into aliquots and lyophilized using the procedure described in a previous study [ 9 ]. It was found in preliminary experiments that these samples were stable for at least 2 years when stored frozen at -20 ° C (Weykamp and Wielders, unpublished).…”

“…The imprecision of CDT determination for both six-level panels was evaluated in five laboratories of the reference laboratories network [ 9 ]. Each sample was measured in duplicate and the inter-laboratory imprecision was calculated for all levels of both panels.…”

“…In a previous WG-CDT study [ 9 ], matrix effects due to 1) and 2) were excluded; the present study therefore focused on the nature of the measurand.…”

“…In its first publication [ 7 ], disialotransferrin (disialylated monoglycan transferrin) was defined as the measurand for a reference method and the target analyte for the standardization work, and high-performance liquid chromatography (HPLC) [ 8 ] with photometric detection was proposed as the candidate reference method. A network of reference laboratories running this method was formed demonstrating good intra-and inter-laboratory performance [ 9 ].…”

Disialo–trisialo bridging of transferrin is due to increased branching and fucosylation of the carbohydrate moiety

“…High performance liquid chromatography (HPLC) of transferrin glycoforms was recommended as the interim reference method to be applied in CDT confirmatory analysis [13]. To overcome the lack of standardization affecting CDT analysis, the Working Group on Standardization of CDT measurement (IFCC-WG-CDT) suggested to use disialotransferrin as the primary target molecule for CDT measurement, expressed as relative amount of total transferrin concentration [13,14]. Although there are great advantages of this method, in particular regarding analytical and clinical specificity, a number of atypical separation patterns, not reflecting alcohol abuse, have been identified.…”