Psychiatrische Klinik der Ludwig-Maximilian-Universität, München, Germany,
1 Zentrallabor, Otto-Wagner-Spital, Wien, Austria,
2 Roche Diagnostics GmbH, Mannheim, Germany,
3 Department of Clinical Neuroscience and Clinical Chemistry, Karolinska Institute, Stockholm, Sweden,
4 Department of Clinical Chemistry, Ziekenhuis Rijnstate, Arnhem and
5 Department of Clinical Chemistry, Ziekenhuizen Noord-Limburg, Venlo, The Netherlands
Received 30 July 2002; in revised form 12 December 2002; accepted 6 January 2003
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ABSTRACT |
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INTRODUCTION |
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CDT can be measured by various commercial immunoassays (Hackler et al., 2000; Anton et al., 2001
; Arndt, 2001
; Myrick et al., 2001
; Schellenberg et al., 2001
; Turpeinen et al., 2001
; Helander, 2002
). International consensus has been reached that these tests should be calibrated against a sensitive high-performance liquid chromatography (HPLC) method separating the a-, mono-, and di-sialo transferrin isoforms (Helander et al., 2001a
; Arndt et al., 2002
). The results should be expressed as a percentage of total transferrin. The recently developed Tina-quant
%CDT 2nd generation assay (Roche Diagnostics GmbH) fulfils these criteriain contrast with the previous Tina-quant
%CDT assay which additionally detects about 50% of tri-sialotransferrin. Aside from adaptation of the new test to an internationally acknowledged standardization procedure, the Tina-quant
%CDT 2nd generation test assay is adapted for runs on high-throughput Roche/Hitachi systems in combination with clinical chemistry and drug testing.
It was the goal of the present multicentre study to test the technical performance characteristics of this new assay under routine conditions. The study was performed in five laboratories (Table 1) according to a standardized protocol.
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MATERIALS AND METHODS |
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The main difference between the Tina-quant %CDT 2nd generation assay and the previous Tina-quant
%CDT test is that tri-sialotransferrin is not included in the CDT fraction. This is achieved by modification of the column separation step. Acceleration of column separation is an additional benefit of this modification. In order to overcome the frequently discussed lack of standardization for CDT immunoassays, the Tina-quant
%CDT 2nd generation assay uses the same standardization procedure as the new Axis-Shield %CDT test (microtitre version) and its different instrument applications (Helander, 2002
). In agreement with this method, the upper limit of the reference range is claimed to be 2.6% by Roche Diagnostics GmbH. The recommended cut-off of the previous Tina-quant
%CDT test is 6.0%.
The Axis-Shield %CDT test (microtitre version) was used as immunochemical comparison method in four laboratories. CDT detection has to be performed manually in this assay. In contrast, the Tina-quant %CDT 2nd generation assay is applied to fully automated Roche/Hitachi systems, which allow a high throughput of CDT measurements in combination with routine clinical chemistry.
In the method comparison studies described here, two HPLC methods (Clin-Rep HPLC, RECIPE plc.; modified Jeppsons HPLC) were included, each of which was employed in one laboratory. Statistical validation of the method comparison studies was performed by PassingBablok regression analysis (Passing and Bablok, 1983).
Studies on the analytical range and on interferences of the new test were performed in the laboratory of the manufacturer. The limit of detection was estimated by 21-fold measurements of 0.9% saline using the CDT application and reported as the mean + 3 SD of these measurements. Linearity was verified for the CDT and the total transferrin application by serial dilutions of samples with approximately 24 mg/l transferrin with 0.9% saline according to a published procedure (Bablok, 1993).
Endogenous interferences according to the Glick model (Glick et al., 1986), as well as drug interferences, were tested on Roche/Hitachi 911. Potential interfering drugs were spiked into a human serum pool at 510-fold concentrations of the maximum daily dosage.
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RESULTS AND DISCUSSION |
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Interferences
No effect of endogenous interferences was found up to approximately 1000 mg/dl of haemoglobin (H index of 1000), 60 mg/dl conjugated and unconjugated bilirubin (I index of 60), highly lipaemic samples (L index of 750, which corresponds to turbidity), and rheumatoid factors up to 1000 IU/ml (data not shown).
Seventeen frequently used drugs were spiked at high concentrations into a human serum pool. As shown in Table 4, the recovery of the CDT target values in the spiked samples was in the range from 92 to 108%. This demonstrates a high resistance of the test against endogenous and drug interferences. However, as with other immunochemical CDT assays, the Tina-quant
%CDT 2nd generation assay bears the risk of erroneous results in cases of rare genetic transferrin variants, which can be identified by HPLC or isoelectric focusing (Helander et al., 2001b
).
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ACKNOWLEDGEMENTS |
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FOOTNOTES |
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Tina-quant is a trademark of a member of the Roche group.
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REFERENCES |
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