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Predicting viremia in anti-HCV positive individuals by using a third generation assay
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Silvia C Sookoian, MD Hospital Argerich. Liver Unit., Gustavo Castaño, MD.
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ssookoian{at}intramed.net Silvia C Sookoian, et al.
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Dear Sir, We read with great interest the article recently published in Clinical Chemical, by Dufour and co-workers (1) regarding low-positive anti- hepatitis C virus enzyme immunoassay results as predictor of low likehood of hepatitis C infection. In this paper, the authors conclude that the S/C ratio is important even in high-risk individuals and laboratories should report the S/C ratio along with anti-HCV EIA results. The most practical screening tests for hepatitis C virus antibodies are second and third- generation enzyme immunoassays (2), but a positive result does not differentiate between viremic and non-viremic patients. To further asses the potential role of the enzyme tests in predicting HCV viremia, we evaluated the performance of different microparticle enzyme immunoassay (MEIA) ratio of the sample rate to the cut-off rate (S/CO) values in the identification of viremic from non viremic anti-HCV positive patients. We studied 106 serum samples of patients seen at the Liver Unit of the Argerich County Hospital during 2000/2001, (57 male and 49 female, mean age 43 years, range 21 to 68) with positive anti-HCV confirmed by a third- generation line immunoassay. The assay 3.0 automatically calculates a result based on the ratio of the sample rate to the cut-off rate for each sample and control (S/CO). In the anti-HCV test, an S/CO equal to or grader than 1.00 was considered reactive. Detection of serum HCV-RNA was performed by a home made reverse- transcription polymerase chain reaction (RT-PCR) in all the samples in at least two different samples using primers from the 5’non coding region of the HCV genome. To evaluate the diagnostic value of the MEIA test in predicting HCV viraemia, anti-HCV positive patients were categorised in two groups according to presence or absence of serum HCV-RNA. S/CO values were analysed in each group; sensitivity, specificity, positive and negative predictive values of different S/CO values in detecting viremic patients were calculated. Receiver-operating characteristic curves, in which the sensitivity is plotted against the false-positive rate (1 – the value of specificity) was generated to evaluate the best cut-off point of the S/CO value of the assay (3). Among the 106 patients, 26 had non detectable serum HCV-RNA and 80 had detectable HCV-RNA by PCR. When the means of S/CO values for patients with detectable and non detectable HCV-RNA were analysed, a statistically significant difference was found, (79.3 SD 22.2 vs. 8.2 SD 6.4, respectively) (p 0.0001). An S/CO value of 26 showed a sensitivity of 99 % and a specificity of 96 % in discriminating both categories of HCV infected patients. In agreement with Dufour and col., our data demonstrate that viremic HCV patients had higher S/CO values in the MEIA test in comparison with non viremic patients. Hence, this assay may be used to predict viraemia in anti-HCV positive individuals. In conclusion, by establishing 26 as cut-off value of the S/CO in the third generation anti-HCV assay, it is possible to differentiate viremic form non viremic patients. This assay has the the advantages of the enzyme immunoassay - is simple to use, allows to process a variety of immune diagnostic tests simultaneously at conventionally settings, has low variability and relatively low expense (2)-, and subsequently, may predict HCV viraemia. In this regard, clinicians may be informed not only about the antibody existence against HCV, but also they may infer that patients having a high S/CO value in the MEIA test may be viremic. REFERENCES 1) Dufour DR, Talastas M, Fernandez MD, Harris B, Straser DB, Seef L. Low-positive anti-Hepatitis C virus enzyme immunoassay results: An important predictor of low likelihood of hepatitis C infection.Clin Chem 2003, 49(3):479-486. 2) Gretch D. National Institutes of Health Consensus Development Conference Panel Statement: Diagnostic test for Hepatitis C. Hepatology 1997;26:43S-47S. 3) Hanley JA, McNeil BJ. The meaning and use of the area under a receiver operating characteristic (ROC) curve. Radiology 1982;143:29-36. |
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