A comparison between two commercial methods for determining carbohydrate deficient transferrin (CDT)

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.

Reflex Testing for Carbohydrate-Deficient Transferrin (CDT) in Insurance Applicants with Elevated High Density Lipoprotein Cholesterol (HDL)

Objectives .- Ascertain the utility of testing carbohydrate deficient transferrin (CDT) levels in insurance applicants with elevated high density lipoprotein cholesterol (HDL) levels. Background .- Chronic alcoholism is not uncommon and is a risk factor for health and longevity and thus of interest to providers of insurance. A number of tests serve as markers of alcohol use, eg, blood alcohol level, elevated liver enzymes, ethyl glucuronide in urine, whole blood associated aldehyde (WBAA), macrocytosis, elevated HDL, elevated CDT and others. WBAA and CDT are usually only done, if some other screening test suggests alcohol use. HDL testing is routinely done for assessing cardiac risk, however, chronic alcohol intake tends to raise HDL and some insurance providers reflex to CDT testing when HDL is elevated. Methods .- A number of the clients of Heritage Labs Inc. have rules in place to test for CDT levels in specimens showing elevated HDL levels. The commonest HDL level that serves as the trigger for reflex testing for CDT is 80mg/dL. The results of this practice were analyzed to assess the utility of reflex testing for CDT to identify chronic alcohol abusers among the applicants. Results .- In examining the results of CDT levels done as a reflex test due to elevated HDL levels, about 2% of the applicants, 0.7% of women and 3% of men, tested positive for elevated CDT levels. Conclusions .- The incidence of elevated CDT levels is high enough to warrant routinely testing for this analyte in applicants, especially men, with high HDL levels.

[Does carbohydrate-deficient transferrin have diagnostic value in non-alcoholic fatty liver disease?]

Non-alcoholic fatty liver disease (NAFLD) is an acquired metabolic liver disease in the consequence of triglyceride accumulation within liver cells. It is accompanied by necrobiotic inflammatory reaction, fibrosis and also by liver cirrhosis. Its distinction from alcoholic fatty liver disease (AFLD) can be difficult. Clear anamnesis may help, but if the patient does not inform us about the alcohol consumption, the differentiation is not easy.

AIM

Our aim was to determine the value of carbohydrate deficient transferrin (CDT) in patients with non-alcoholic fatty liver disease, as well as to analyze the background of high CDT values, according to the anamnesis.

PATIENTS AND METHODS

39 patients (21 female and 18 male) with ultrasound signs of fatty liver disease were studied. CDT, body mass index (BMI) and HOMA index were determined.

RESULTS

Mean value of CDT was: 2.39+/-0.52% (in male 2.51+/-0.61, in female 2.28+/-0.4). No significant difference was found among the two sexes. The diversity of CDT values was normal. The value of BMI belonged to the overweight area without any significant difference between the two sexes.

CONCLUSION

On the basis of the results, NAFLD and AFLD can be differentiated according to the CDT value, and this value could be a higher specific value than the activity of gammaglutamyl transpeptidase, however, anamnesis and other factors are as well very important in achieving the correct diagnosis.

Carbohydrate-deficient Transferrin as a Marker of Chronic Alcohol Abuse: A Critical Review of Preanalysis, Analysis, and Interpretation

Background: Carbohydrate-deficient transferrin (CDT) is used for diagnosis of chronic alcohol abuse. Some 200–300 reports on CDT have been published in impact factor-listed journals. The aims of this review were to condense the current knowledge and to resolve remaining issues on CDT.

Approach: The literature (1976–2000) was searched using MEDLINE and Knowledge Server with “alcohol and CDT” as the search items. The data were reviewed systematically, checked for redundancy, and organized in sequence based on the steps involved in CDT analysis.

Content: The review is divided into sections based on microheterogeneity of human serum transferrin (Tf), definition of CDT, structure of human serum CDT, pathomechanisms of ethanol-induced CDT increase, preanalysis, analysis, and medical interpretation (postanalysis). Test-specific cutoff values for serum CDT and causes of false positives and negatives for chronic alcohol abuse are discussed and summarized.

Summary: Asialo- and disialo-Fe2-Tf, which lack one or two complete N-glycans, and monosialo-Fe2-Tf (structure remains unclear) are collectively referred to as CDT. Diminished mRNA concentration and glycoprotein glycosyltransferase activities involved in Tf N-glycan synthesis and increased sialidase activity most likely account for alcohol-induced increases in CDT. Knowledge about in vivo and in vitro effects on serum CDT is poor. Reliable CDT and non-CDT fractionation is needed for CDT measurement. Analysis methods with different analytical specificities and recoveries decreased the comparability of values and statistical parameters of the diagnostic efficiency of CDT. CDT is the most specific marker of chronic alcohol abuse to date. Efforts should concentrate on the pathomechanisms (in vivo), preanalysis, and standardization of CDT analysis.

Carbohydrate-deficient transferrin is not a useful marker for the detection of chronic alcohol abuse

BACKGROUND

The role of carbohydrate-deficient transferrin (CDT) as a reliable marker for the detection of chronic alcohol abuse has been discussed controversially.

METHODS

Therefore, we investigated CDT in the sera from 405 subjects with different alcohol intake. Besides healthy control subjects (n = 42), inpatients and outpatients in a department of gastroenterology (n = 325) and patients admitted to a department of otorhinolaryngology (n = 38) were studied. A total of 213 patients suffered from various forms of liver diseases, and 89 patients had liver transplantation. CDT values were determined by a double-antibody radioimmunoassay.

RESULTS

In the 241 alcohol-abstinent subjects, CDT levels ranged from 3 to 90 units L-1 (median = 12); the 92 moderate drinkers (20-60 g of alcohol per day) showed values from 3 to 40 units L-1 (median = 12), and the 72 subjects with chronic alcohol abuse (> 60 g per day) revealed CDT levels from 3 to 100 units L-1 (median = 16). The diagnostic specificity for alcohol abuse was 86.8% for men (sensitivity 36.9%) and 95% for women (sensitivity 0%).

CONCLUSION

Our data indicate that measurement of CDT does not reach clinical use in the detection of chronic alcohol abuse in an unselected population because of its insufficient specificity and sensitivity.

Validation by isoelectric focusing of the anion-exchange isotransferrin fractionation step involved in determination of carbohydrate-deficient transferrin by the CDTect assay

Serum concentration of carbohydrate-deficient transferrin (CDT) is used for laboratory diagnosis of chronic alcohol abuse. Using isoelectric focusing for validation of the initial isotransferrin fractionation step involved in the determination of CDT by the CDTect assay, we found a complete in vitro iron saturation of transferrin and sufficient stability of the transferrin iron load during column passage; effective separation of non-CDT-isotransferrins and CDT-isotransferrins at the microcolumns; partial coelution of trisialo-Fe2-transferrin, which did not significantly affect CDT measurement; partial retention of CDT-isotransferrins, especially disialo-Fe2-transferrin, which may cause falsely negative results for CDT at the upper reference limits; good precision of the isotransferrin fractionation step; and no significant effects of low concentrations of serum protein and transferrin. We strongly urge standardization of CDT analysis and suggest isoelectric focusing for validation of CDT analysis methods and verification of odd results.

Quantification of carbohydrate-deficient transferrin by ion-exchange chromatography with an enzymatically prepared calibrator

The current HPLC method for the determination of carbohydrate-deficient transferrin (CDT) yields ratios of CDT isoforms in relation to total transferrin, whereas the use of absolute concentrations obtainable in routine analysis by RIA and the reference ranges based hereupon is more convenient. We describe a modified HPLC method that likewise gives absolute CDT concentrations by using a calibrator prepared by treatment of transferrin with neuraminidase. Separation of isoforms could be improved and analysis time reduced to ∼2 h. Iron saturation proved stable during chromatography. In contrast to a commercial RIA, the cheaper and more time-saving HPLC method excludes erroneous results caused by aged samples or genetic transferrin variants and enables the determination of asialo- and disialotransferrin. Both methods showed comparable precision and correlated with each other (y = 1.76 + 0.27x; Sy|x = 5.38); for the HPLC method precision was 1.3–9.8% (within assay) and 6.2–10.6% (between assay). The clinical evaluation with a cutoff concentration of 80 mg/L resulted in a diagnostic specificity of 100% and a sensitivity of 82.5%.

Increased serum concentration of carbohydrate-deficient transferrin in patients with combined pancreas and kidney transplantation

Serum concentration of carbohydrate-deficient transferrin (cCDT) is used for laboratory diagnosis and follow-up of chronic alcohol abuse. In analyzing by CDTect-RIA (Pharmacia) sera from outpatients with combined pancreas and kidney transplantation and no excessive alcohol consumption, we found above-normal values for cCDT and CDT/transferrin ratios (CDT/Tf) in more than half of the samples. Isoelectric focusing of these samples showed distinct bands of carbohydrate-deficient isotransferrins, supporting the abnormal findings from the CDTect assay. In contrast, diabetics and outpatients who had received only kidney transplants showed normal values for cCDT, CDT/Tf, and isotransferrin patterns. Increased serum Tf, sialidase-producing microorganisms, and immunosuppressive medication were eliminated as causes of these abnormal cCDT and CDT/Tf results. Successful pancreas transplantation leads to hyperinsulinemia and normoglycemia, in contrast to hypoinsulinemia and hyperglycemia in the patients who receive kidney transplants alone. These factors may have pathogenic importance for CDT increase, yielding results falsely interpreted as positive with respect to alcohol abuse in patients with combined pancreas and kidney transplantation.

Biological markers of alcohol consumption and effect of calcitonin in nonalcoholic men: a prospective, double-blind study

The objective of this study was to study the ability of biological markers of alcohol consumption in differentiating subjects below weekly consumption of 400 or 600 g of absolute ethanol from those above, and to study the effect of intranasal calcitonin on alcohol drinking. A prospective 12-week double-blind study that used anonymous data collection with drinking diaries was done. The drug that was studied (calcitonin or placebo) was used during study weeks 5-8. This study was performed at the research unit of a university hospital. The subjects consisted of 59-nine men aged 26 to 57 years who considered themselves as regular but modest drinkers and were recruited by advertisements. The measurements were obtained from monthly questionnaires and daily anonymous diaries for alcohol drinking data, and biological markers of alcohol consumption (aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transpeptidase, beta hexosaminidase, and carbohydrate deficient transferrin). The results indicated intranasal calcitonin with a dose of 200 IU three times a week had no effect on alcohol use. All biological markers studied had only a modest ability to differentiate those with weekly alcohol consumption of 400 or 600 g or over from those below these limits. The areas under receiver operating characteristic (ROC) curve with the limit 400 g/week were 0.71 for aspartate aminotransferase, 0.61 for alanine aminotransferase, 0.74 for gamma-glutamyl transpeptidase, 0.68 for beta-hexosaminidase, and 0.78 for carbohydrate deficient transferrin. Respective numbers for the 600-g limit were more uniform. As evaluated by ROC analysis, carbohydrate deficient transferrin was the best biological marker to find men with weekly alcohol consumption over 400 g. Intranasal salmon calcitonin had no affect on alcohol drinking.

Sensitivity and specificity of carbohydrate-deficient transferrin as a marker of alcohol abuse are significantly influenced by alterations in serum transferrin: comparison of two methods

Despite a number of investigations suggesting the value of carbohydrate-deficient transferrin (CDT) as a marker of alcohol abuse, a variety of issues on the applicability of CDT measurements in clinical settings have remained unexplored. Earlier studies in this field have focused on the relationship of CDT and the amount of alcohol consumption or presence of liver disease, whereas the influence of alterations in serum transferrin concentrations on CDT has received less attention. In this study, we compared two different methods for measuring CDT (CDTect and %CDT) and total transferrin concentrations in a sample of 83 alcohol abusers (20 patients with alcoholic liver disease and 63 heavy drinkers who were devoid of liver disease, despite excessive alcohol consumption) and 89 controls, who were social drinkers or abstainers. The control population included 53 hospitalized patients with expected abnormalities in serum transferrin concentrations caused by conditions such as negative iron balance, pregnancy, or nonalcoholic liver disease. Both methods gave significantly higher values in alcohol abusers than in controls (p < 0.01), but the overall sensitivity for detecting alcohol abuse was clearly higher for CDTect (59%) than for %CDT (34%). The correlation between the results obtained by the two methods (r = 0.629) significantly improved, when the CDTect values were replaced by the ratio of CDTect/total transferrin (r = 0.770) (p < 0.05). There was a positive correlation between the CDTect and serum transferrin (r = 0.201, p < 0.01), which was significant both in the alcoholics (r = 0.240, p < 0.05), and especially in the controls (r = 0.727, p < 0.001). A significant inverse correlation emerged between %CDT and total transferrin (r = -0.302, p < 0.01). The sensitivities of CDTect and %CDT for correctly classifying alcohol abusers in the subgroup of alcoholic liver disease patients were 90% and 70% and in the subgroup of heavy drinkers without liver disease (49% and 22%), respectively. Specificities for CDTect and %CDT in this sample were 81% and 100%, respectively. However, in the subgroup of hospitalized control patients with abnormal serum transferrin, the specificity of CDTect was only 48%. According to present data, CDTect seems to be more sensitive than %CDT for detecting alcohol abuse. However, any alteration in serum total transferrin concentration markedly decreases the assay specificity. This should be considered when interpreting the assay results in patients with elevated serum transferrin, such as iron deficiency, pregnancy, or liver diseases.

Carbohydrate-deficient transferrin as a marker of alcohol abuse: relationship to alcohol consumption, severity of liver disease, and fibrogenesis

Carbohydrate-deficient transferrin (CDT) measurements have been widely examined as a marker of excessive alcohol consumption, yet the information on the sensitivity of this method has remained controversial. In addition, little is known of the relationship of this marker and the severity of alcoholic liver disease (ALD). To clarify these issues, we analyzed serum samples from 373 alcohol abusers, including 200 problem drinkers with no apparent liver pathology, 173 patients with clinical or morphological evidence of ALD, and 42 healthy controls. CDT was analyzed by anion-exchange chromatography followed by radioimmunoassay. At a specificity of 100%, the sensitivity of CDT was 36% in problem drinkers reporting a mean of 710 +/- 80 (mean +/- 2SE) g of ethanol/week, as compared with the sensitivities of 44% and 35% for gamma-glutamyltranspeptidase (GGT) and mean corpuscular volume (MCV), respectively. In a subgroup of problem drinkers (n = 51) with the highest ethanol intakes (1160 +/- 180 g of ethanol/week) and severe dependence, the sensitivity of CDT increased to 64%, compared with 55% for GGT and 39% for MCV. In ALD, the CDT values were significantly higher than in the alcoholics with nonliver pathology. However, when such patients were classified according to the clinical, laboratory, and morphological severity of liver disease, CDT was found to be primarily elevated in those with the early stage of ALD, such that there was a significant negative correlation between CDT and the combined morphological index of disease severity (rs = -0.315, p < 0.05). ALD markers of fibrogenesis were elevated more frequently than CDT, showing significant positive correlations with the indices of disease severity.(ABSTRACT TRUNCATED AT 250 WORDS)