Harmonization of Measurement Results of the Alcohol Biomarker Carbohydrate-Deficient Transferrin by Use of the Toolbox of Technical Procedures of the International Consortium for Harmonization of Clinical Laboratory Results

Brief history of the alcohol biomarkers CDT, EtG, EtS, 5-HTOL, and PEth

This article traces the historical development of various biomarkers of acute and/or chronic alcohol consumption. Much of the research in this domain of clinical and laboratory medicine arose from clinics and laboratories in Sweden, as exemplified by carbohydrate deficient transferrin (CDT) and phosphatidylethanol (PEth). Extensive studies of other alcohol biomarkers, such as ethyl glucuronide (EtG), ethyl sulfate (EtS), and 5-hydroxytryptophol (5-HTOL), also derive from Sweden. The most obvious test of recent drinking is identification of ethanol in a sample of the person's blood, breath, or urine. However, because of continuous metabolism in the liver, ethanol is eliminated from the blood at a rate of 0.15 g/L/h (range 0.1-0.3 g/L/h), so obtaining positive results is not always possible. The widow of detection is increased by analysis of ethanol's non-oxidative metabolites (EtG and EtS), which are more slowly eliminated from the bloodstream. Likewise, an elevated ratio of serotonin metabolites in urine (5-HTOL/5-HIAA) can help to disclose recent drinking after ethanol is no longer measurable in body fluids. A highly specific biomarker of hazardous drinking is CDT, a serum glycoprotein (transferrin), with a deficiency in its N-linked glycosylation. Another widely acclaimed biomarker is PEth, an abnormal phospholipid synthesized in cell membranes when people drink excessively, having a long elimination half-life (median ~6 days) during abstinence. Research on the subject of alcohol biomarkers has increased appreciably and is now an important area of drug testing and analysis.

Recommendations on the measurement and use of the alcohol consumption biomarker CDT. A position paper from the IFCC Working Group on CDT standardisation

BACKGROUND

Carbohydrate deficient transferrin (CDT) is a biomarker for excessive alcohol consumption utilized in clinical and forensic medicine and workplace testing. Previously, many different analytical methods for CDT were used and the measurand varied considerably, making direct comparison of test results difficult. To end this confusion, the IFCC established a working group on CDT standardisation (WG-CDT) which completed its tasks in 2017.

METHODS

This IFCC position paper by the WG-CDT summarizes state of the art information about the measurand and the analytical methods and gives concise recommendations for its utilization.

RESULTS

The results achieved by the CDT standardisation process led to accuracy improvements in national external quality assessment schemes over the years. A brief review of ROC based comparison studies with the traditional biomarkers (GGT, MCV, ALT and AST) discusses the bias resulting from inadequate study populations. In large groups of the general population the superior diagnostic performance of CDT is confirmed.

CONCLUSION

The relationship between alcohol intake versus resulting CDT is discussed as well as the cutoff and measurement uncertainty. Concerning the application in practice, potential pitfalls are considered and recommendations handling both analytical and preanalytical caveats are given. Finally, some examples of serious misunderstandings in publications about CDT are addressed.

A novel high-throughput liquid chromatography assay for Carbohydrate-Deficient transferrin (CDT) based on flow-modulated isocratic elution and terbium-induced fluorescence

Transferrin is a glycoprotein containing two bi- or tri-antennary carbohydrate chains ending with sialic acid. Its glycosylation is reduced in chronic alcohol abuse and in inborn glycosylation pathologies, where the carbohydrate-deficient fraction of the protein (CDT) increases significantly. The current methods require a gradient chromatographic separation and time-consuming sample preparation. In comparison, the proposed approach uses a novel flow-modulated liquid chromatography technique (fmLC) and a highly selective and sensitive fluorescence derivatization reaction with terbium ion. A fmLC-FLD method using isocratic anion exchange separation was optimized and validated to resolve disialo-transferrin and trisialo-transferrin from other transferrin glycoforms. Detection took place by recording fluorescence at 550 nm wavelength (excitation at 298 nm). The chromatographic separation needed 5 min, allowing seriate injection every 7.5 min. The method was validated according to the current guidelines of analytical chemistry showing adequate accuracy and precision for the quantitative determination of CDT. The proposed method proved also to be suitable to analyse haemolyzed sera which, because of interference by haemoglobin, fail the standard HPLC-Vis analysis. The method was tested in parallel with HPLC-Vis on 131 sera showing an excellent correlation of results proved by a correlation coefficient of 0.995 (Pearson's r). The proposed approach proved much simpler than the current methods and cheaper in terms of instrumental costs offering a ground-breaking analytical tool that could likely make available the characterization of CDT outside specialized laboratories, such as in occupational medicine centres, doctor's offices, small laboratories, alcohol rehabilitation centres, and in developing countries.

Assessment of alcohol consumption in depression follow-up using self-reports and blood measures including inflammatory biomarkers

AIMS

Alcohol consumption has been suggested a major role in the pathogenesis and prognosis of depression. However, reliable identification of hazardous drinking continues to be problematic. We compared the accuracy of different biomarkers and self-reports of alcohol consumption in the follow-up study of depression.

METHODS

Data from 202 patients with major depressive disorder were obtained through self-reports, AUDIT and AUDIT-C questionnaires and biomarker analyses. The clinical assessments and measurements of biomarkers (GT, CDT, GT-CDT-combination, MCV, ALT, AST, hs-CRP, IL-6) were performed at baseline and after six months of treatment. Based on self-reported alcohol intake at baseline the patients were classified to three subgroups.

RESULTS

About 27.2% of patients were categorized to high-risk drinkers, 26.3% low-risk drinkers and 46.5% abstainers. High-risk drinkers showed significantly higher mean values of GT, CDT, GT-CDT-combination and IL-6 than abstainers, diagnostic accuracy being highest with the combined marker of GT-CDT. The accuracy of AUDIT and AUDIT-C to detect high-risk drinking was also significant. During follow-up, the differences observed in the biomarkers at baseline disappeared together with recovery from depression.

CONCLUSIONS

Our data suggest the combined use of GT-CDT and AUDIT questionnaires to improve the identification of drinking of patients with depression. This approach could be useful for improving treatment adherence and outcome in depressed patients.

Carbohydrate-deficient transferrin: utility of HPLC in handling atypical samples uninterpretable by capillary electrophoresis

HPLC retesting allowed to resolve about half of the most common CDT patterns uninterpretable by CE. The usefulness of this approach should be evaluated in the specific context of each laboratory.

The roadmap for harmonization: status of the International Consortium for Harmonization of Clinical Laboratory Results

The International Consortium for Harmonization of Clinical Laboratory Results (ICHCLR) was established to fulfill recommendations identified by an international conference convened to review the available infrastructure and challenges in achieving harmonization of results among different measurement procedures. The specific objectives of the ICHCLR are to: prioritize measurands by medical importance, coordinate the work of different organizations, and stimulate development of technical and regulatory processes to achieve harmonization. Central to these objectives is the website “www.harmonization.net” developed by the ICHCLR as an information portal designed to provide a resource center for global activities to harmonize and standardize results from clinical laboratory measurement procedures. Priorities based on medical impact are provided for measurands for which harmonization is needed or work to implement harmonization is incomplete or inactive. By making information available regarding harmonization activities in progress or planned, coordination of work to harmonize laboratory measurement procedures will minimize duplication of effort and optimize the use of limited resources. A toolbox of technical procedures developed by ICHCLR to be considered when developing a process to achieve harmonization for a measurand is presented. The ICHCLR initiated a proposal to ISO Technical Committee 212 for a harmonization protocol as the basis for calibration traceability when there are no other higher order reference system components available. The ICHCLR offers a unique service to prioritize measurands in need of harmonization and to provide a centralized approach to organize global efforts to achieve harmonization of clinical laboratory test results.

The quest for equivalence of test results: the pilgrimage of the Dutch Calibration 2.000 program for metrological traceability

Calibration 2.000 was initiated 20 years ago for standardization and harmonization of medical tests. The program also intended to evaluate adequate implementation of the In Vitro Diagnostics (IVD) 98/79/EC directive, in order to ensure that medical tests are fit-for-clinical purpose. The Calibration 2.000 initiative led to ongoing verification of test standardization and harmonization in the Netherlands using commutable external quality assessment (EQA)-tools and a type 1 EQA-design, where feasible. National support was guaranteed by involving all laboratory professionals as well as laboratory technicians responsible for EQA and quality officers. A category 1 EQA-system for general chemistry analytes, harmonizers for specific analytes like hGH and IGF-1, and commutable materials for other EQA-sections have been developed and structurally introduced in the EQA-schemes. The type 1 EQA-design facilitates the dialogue between individual specialists in laboratory medicine and the IVD-industry to reduce lot-to-lot variation and to improve standardization. In such a way, Calibration 2.000 sheds light on the metrological traceability challenges that we are facing and helps the laboratory community to get the issues on the table and resolved. The need for commutable trueness verifiers and/or harmonizers for other medical tests is now seen as paramount. Much knowledge is present in the Netherlands and for general chemistry, humoral immunology and protein chemistry, a few endocrinology tests, and various therapeutic drug monitoring (TDM) tests, commutable materials are available. Also the multi sample evaluation scoring system (MUSE) and the category 1 EQA-design offer many possibilities for permanent education of laboratory professionals to further improve the between and within laboratory variation and the test equivalence.

Monitoring of transferrin isoforms in biological samples by capillary electrophoresis

Work dealing with the monitoring of transferrin isoforms in human serum and other body fluids by capillary electrophoresis is reviewed. It comprises capillary zone electrophoresis and capillary isoelectric focusing efforts that led to the exploration and use of assays for the determination of carbohydrate-deficient transferrin as a marker for excessive alcohol intake, genetic variants of transferrin, congenital disorders of glycosylation and β-2-transferrin, which is a marker for cerebrospinal fluid leakage. This paper provides insight into the development, specifications, strengths, weaknesses, and routine use of the currently known capillary electrophoresis based assays suitable to detect transferrin isoforms in body fluids. The achievements reached so far indicate that capillary zone electrophoresis is an attractive technology to monitor the molecular forms of transferrin in biological specimens as the assays do not require an elaborate sample pretreatment and thus can be fully automated for high-throughput analyses on multicapillary instruments. Assays based on capillary isoelectric focusing are less attractive. They require immunoextraction of transferrin from the biological matrix and mobilization after focusing if instrumentation with a whole-column imaging detector is not available. Interactions of the carrier ampholytes with the iron of transferrin may prevent iron saturation and thus provide more complicated isoform patterns.

Why measure carbohydrate deficient transferrin?

The acute or chronic harmful use of alcohol is among the top five risk factors for disease, disability and death worldwide.1 Monitoring alcohol consumption is an important aspect of the management of alcohol-use disorders and may include subjective self-reported questionnaires or objective tests.1,2-6 Such tests include measuring alcohol or alcohol metabolite levels or biomarkers such as liver enzymes or red cell indices.2-6 Carbohydrate deficient transferrin (CDT) is a biomarker used for assessing chronic alcohol misuse.6 Here, we review CDT and its place in the assessment of chronic alcohol use.

Assays of Gamma-Glutamyl Transferase and Carbohydrate-Deficient Transferrin Combination from Maternal Serum Improve the Detection of Prenatal Alcohol Exposure

BACKGROUND

Alcohol use during pregnancy leads to detrimental effects on fetal development. As self-reports by mothers are known to be unreliable for assessing prenatal alcohol exposure, there is a need for sensitive and specific biomarkers for identifying those at risk for alcohol-affected offspring.

METHODS

We measured serum gamma-glutamyl transferase (GGT), carbohydrate-deficient transferrin (CDT), a mathematically formulated combination of GGT and CDT (GGT-CDT), and ethylglucuronide (EtG) concentrations from 1,936 mothers with a positive (n = 480) or negative (n = 1,456) history of alcohol use at the time of pregnancy. The material included 385 alcohol-abusing mothers who subsequently gave birth to children with fetal alcohol syndrome (FAS) and 1,551 mothers without FAS children including 95 women who reported a median of 1.0 standard drinks of alcohol per day during pregnancy and 1,456 nondrinking controls. Among those without FAS outcome, there were 405 mothers with gestational diabetes mellitus (GDM) and 745 mothers representing lifelong abstainers.

RESULTS

Mothers of FAS children had higher mean GGT, CDT, GGT-CDT, and EtG levels than abstainers (p < 0.001 for all comparisons) or mothers reporting some alcohol consumption but whose children were not diagnosed with FAS (p < 0.001 for all comparisons). In receiver operating characteristic analyses using cutoffs based on abstainers, the area under the curves (AUCs) for GGT-CDT (0.873) were higher than those of GGT (0.824), CDT (0.776), or EtG (0.584) for differentiating the mothers of FAS children and abstainers. Unlike CDT, this combination marker also differed significantly between drinking mothers without FAS outcome and abstainers (AUC = 0.730, p < 0.001). In comparisons adjusted for GDM and body mass index, the group of mothers who had reported a median of 1.0 standard drinks of alcohol per day during pregnancy also differed from the group reporting no current alcohol intake in GGT (p < 0.02) and GGT-CDT (p < 0.01) levels.

CONCLUSIONS

Combination of GGT and CDT improves the identification of prenatal alcohol exposure and associated high-risk pregnancies. A more systematic use of biomarkers may help intervention efforts to prevent alcohol-induced adverse effects on fetal development.

Affinity Capillary Electrophoresis for Selective Control of Electrophoretic Mobility of Sialic Acid Using Lanthanide-Hexadentate Macrocyclic Polyazacarboxylate Complexes

It is difficult to control the electrophoretic mobility in order to obtain high resolution among saccharides in complex samples. We report herein on a new affinity capillary electrophoresis (ACE) method for an anionic monosaccharide, N-acetylneuraminic acid (Neu5Ac), which is important in terms of pathological diagnosis, using lanthanide-hexadentate macrocyclic polyazacarboxylate complexes (Ln-NOTA) as affinity reagents. It was shown that Ln-NOTA complexes increased the anionic mobility of Neu5Ac by approximately 40% through selective complexation with Neu5Ac. The extent of change in the mobility strongly depended on the type of central metal ion of Ln-NOTA. The stability constant (K) of Lu-NOTA with Neu5Ac was determined by ACE to be log Kb = 3.62 ± 0.04, which is the highest value among artificial receptors for Neu5Ac reported so far. Using this ACE, the Neu5Ac content in a glycoprotein sample, α1-acid glycoprotein (AGP), was determined after acid hydrolysis. Complete separation between Neu5Ac and hydrolysis products was successful by controlling the mobility to determine the concentration of Neu5Ac.

Carbohydrate-Deficient Transferrin Determination in a Clinical Setting: Consistency Between Capillary Electrophoresis Assays and Utility of HPLC as a Confirmatory Test

BACKGROUND

Carbohydrate-deficient transferrin (CDT) is used to assess chronic alcohol consumption in administrative and forensic context. The aim of the present study was the optimization of the diagnostic strategy for CDT determination in a clinical laboratory setting.

METHODS

Two capillary zone electrophoresis (CZE) assays, the CEofix CDT (Analis, Suarlée, Belgium) run on single capillary MDQ instrument and the muticapillary (Sebia, Lisses, France), were compared as screening methods and a commercial high-performance liquid chromatography (HPLC) assay (Recipe, Munich, Germany) was used for confirmation.

RESULTS

In total, 367 serum samples were analyzed by both CZE assays with concordant classification in 92% of cases. All discordant samples were classified as negative by HPLC, as did 2/3 of those that could not be classified by either CZE assay. Classification of samples with CDT values close to cut-off by CZE was confirmed by HPLC in 95-100% of negative samples but only in 28.6-33.3% of positive samples.

CONCLUSIONS

Both CZE assays proved suitable for CDT screening. HPLC was useful for discriminating CDT value in most of samples that could not be interpreted by CZE due to analytical interferences. Considering the implication of CDT testing, HPLC assay may also be helpful for the confirmation of positive results close to the cut-off value of CZE assays.