International collaborative study on the second EUROHEP HCV-RNA reference panel

Standardization of NAT for Blood-Borne Pathogens

Assays based on nucleic acid amplification technology (NAT) are increasingly used for screening of blood and for diagnosis or monitoring of patients. Both regulatory requirements for blood screening and international recommendations for the treatment of patients are based on common reference materials available globally for the standardization of NAT assays. World Health Organization International Standards (WHO ISs) and International Reference Panels (WHO IRPs) are primary reference materials. The characterization and manufacture of WHO reference materials as well as their evaluation is performed on behalf of the WHO by collaborating centers; their establishment is decided upon by the WHO Expert Committee on Biological Standardization (ECBS). The potency of the first WHO IS is defined by the 'international unit' (IU) which should be maintained upon replacement of the IS. The IU, unlike copy number or genome equivalent, is defined by the IS with a physical existence, is available worldwide, and allows traceability and comparability of results. The anticipated use of WHO ISs is the calibration of secondary standards or the validation of essential assay features, e.g. limit of detection.

Principles and applications of polymerase chain reaction in medical diagnostic fields: a review

Recent developments in molecular methods have revolutionized the detection and characterization of microorganisms in a broad range of medical diagnostic fields, including virology, mycology, parasitology, microbiology and dentistry. Among these methods, Polymerase Chain Reaction (PCR) has generated great benefits and allowed scientific advancements. PCR is an excellent technique for the rapid detection of pathogens, including those difficult to culture. Along with conventional PCR techniques, Real-Time PCR has emerged as a technological innovation and is playing an ever-increasing role in clinical diagnostics and research laboratories. Due to its capacity to generate both qualitative and quantitative results, Real-Time PCR is considered a fast and accurate platform. The aim of the present literature review is to explore the clinical usefulness and potential of both conventional PCR and Real-Time PCR assays in diverse medical fields, addressing its main uses and advances.

Interlaboratory comparison of cytomegalovirus viral load assays

To assess interlaboratory variability in qualitative and quantitative cytomegalovirus (CMV) viral load (VL) testing, we distributed a panel of samples to 33 laboratories in the USA, Canada and Europe who performed testing using commercial reagents (n = 17) or laboratory-developed assays (n = 18). The panel included two negatives, seven samples constructed from purified CMV nucleocapsids in plasma (2.0-6.0 log(10) copies/mL) and three clinical plasma samples. Interlaboratory variation was observed in both actual (range, 2.0-4.0 log(10) copies/mL) and self-reported lower limits of detection (range, 1.0-4.0 log(10) copies/mL). Variation observed in reported results for individual samples ranged from 2.0 log(10) (minimum) to 4.3 log(10) (maximum)(.) Variation was greatest at low VLs. Assuming +/- 0.5 log(10) relative to the expected result represents an acceptable result, 57.6% of results fell within this range. Use of commercially available reagents and procedures was associated with less variability compared with laboratory-developed assays. Interlaboratory variability on replicate samples was significantly greater than intralaboratory variability (p < 0.0001). The significant interlaboratory variability in CMV VL observed may be impacting patient care and limiting interinstitutional comparisons. The creation of an international reference standard for CMV VL assay calibration would be an important step in quality improvement of this laboratory tool.

External quality assessment for the molecular detection of Hepatitis C virus

BACKGROUND, OBJECTIVES AND STUDY DESIGN: External quality assessment (EQA) panels were distributed internationally by UK NEQAS for Microbiology to 159 participants for the detection, quantification and genotyping of Hepatitis C virus (HCV) in freeze-dried plasma from 2000 to 2004. The results were analysed to determine the level of standardisation of qualitative detection, quantitative detection and genotyping.

RESULTS

The accurate detection of HCV in the panels varied from 86.9% to 100%. Four genotypes were distributed with the panels and there was no significant difference in the detection of different genotypes of HCV by participants. Further analysis indicated most variation occurred in quantification of HCV at lower concentrations and from 0% to 14.8% reported quantitative values outside 0.5 log(10) of the median value. In addition, three negative specimens were distributed and false positives were found to be rare (0.9-2.2%) with all methods included in the study.

CONCLUSION

The laboratory detection of HCV in plasma EQA specimens was varied, with decreasing parity of quantification at lower concentrations of HCV. False positives and negatives were rare, irrespective of the genotype under test.

Compartmentalization of hepatitis C virus genotypes between plasma and peripheral blood mononuclear cells

Differences in hepatitis C virus (HCV) variants of the highly conserved 5' untranslated region (UTR) have been observed between plasma and peripheral blood mononuclear cells (PBMC). The prevalence and the mechanisms of this compartmentalization are unknown. Plasma and PBMC HCV variants were compared by single-strand conformation polymorphism (SSCP) and by cloning or by genotyping with a line probe assay (LiPA) in 116 chronically infected patients, including 44 liver transplant recipients. SSCP patterns differed between compartments in 43/109 analyzable patients (39%). Differences were significantly more frequent in patients with transplants (21/38 [55%] versus 22/71 [31%]; P < 0.01) and in those who acquired HCV through multiple transfusions before 1991 (15/20; 75%) or through drug injection (16/31; 52%) than in those infected through an unknown route (7/29; 24%) or through a single transfusion (5/29; 17%; P < 0.001). Cloning of the 5' UTR, LiPA analysis, and nonstructural region 5B sequencing revealed different genotypes in the two compartments from 10 patients (9%). In nine patients, the genotype detected in PBMC was not detected in plasma and was weak or undetectable in the liver in three cases. This genotypic compartmentalization persisted for years in three patients and after liver transplantation in two. The present study shows that a significant proportion of HCV-infected subjects harbor in their PBMC highly divergent variants which were likely acquired through superinfections.

Cost effectiveness of testing strategies for chronic hepatitis C

OBJECTIVE

This paper compares nine strategies for determining hepatitis C antibody and viral status. They combine two tests for antibodies (enzyme immunoassays (EIA), recombinant immunoblot assays (RIBA)) and one for viremia (reverse transcription polymerase chain reaction (PCR)). Using optical density to divide EIA results into three categories (high positive, low positive, negative) was also considered.

METHODS

Decision analysis compared strategies on cost as well as sensitivity and specificity with regard to antibody and viral status. Parameters in the decision tree included antibody prevalence, proportion viremic, sensitivity, specificity, and cost of individual tests.

RESULTS

The two best strategies are EIA followed by PCR (EIA-->PCR); and EIA with three levels of optical density (EIA-OD), followed by RIBA for EIA-OD low positives, and then PCR for all positives (EIA-OD-->RIBA-->PCR). EIA-->PCR has equal viral sensitivity, slightly lower cost, slightly higher antibody sensitivity, but lower antibody specificity compared to EIA-OD-->RIBA-->PCR. The cost per false antibody positive avoided using EIA-OD-->RIBA-->PCR rather than EIA-->PCR is $36 when prevalence is 5%, and $193 when prevalence is 50%. Using EIA-OD-->RIBA-->PCR rather than EIA-->PCR results in 112 false antibody positives avoided for every true antibody positive missed when prevalence is 5%; this ratio is 18:1 when prevalence is 25%; and 6:1 when prevalence is 50%.

CONCLUSIONS

EIA-OD-->RIBA-->PCR is the best choice when prevalence in the tested group is below 20%. As prevalence increases, the choice of EIA-OD-->RIBA-->PCR versus EIA-->PCR will depend on the relative importance of avoiding false antibody positives versus missing true antibody positives. Our analysis makes explicit the magnitude of this trade-off.

Variable ratio of hepatitis C virus RNA to viral core antigen in patient sera

Quantification of hepatitis C virus (HCV) core antigen and RNA in serum samples leads to a highly variable ratio of both. It is not clear whether this is due to the inaccuracy of RNA quantification or whether both are independent parameters in a certain range. We established a real-time reverse transcription (RT)-PCR for HCV RNA that combines very high sensitivity with a large dynamic range and minimal standard deviations. The assay was calibrated with the first international standard, 96/790, and the international genotype panel for HCV from the National Institute of Biological Standardisation and Control. A linear readout was obtained between 200 and 5 x 10(7) IU/ml. The detection limit was 80 IU/ml, the reproducibility was <0.05 log, and the standard error within one run was <0.01. Comparison of the method with the Roche Monitor competitive RT-PCR revealed its high accuracy. The core protein concentration was determined within a range from 1.5 to 400 pg/ml by using the preliminary trak-C assay from Ortho Clinical Diagnostics. Correlating the HCV RNA levels with core antigen concentrations in 197 serum samples from 23 interferon-treated patients, a average ratio of 7,900 IU of HCV RNA per pg of core antigen was estimated, but the variability of this ratio exceeded largely the variability of the two assays, ranging from 50 to 20,000 IU/pg. Theoretically, HCV should contain ca. 43,000 IU of RNA/pg core. In conclusion, the core antigen assay seems to detect, in addition to complete virions, RNA-free core protein structures, which enhances its sensitivity (98% in this group). The variable ratio of RNA and core protein is not mainly due to standard deviations of quantification but could be an additional parameter for treatment follow-up and state of viral replication.

Inter-laboratory comparison of qualitative and quantitative detection of hepatitis C (HCV) virus RNA in diagnostic virology: a multicentre study (MS) in Italy

BACKGROUND

The importance of the standardisation of nucleic acid amplification technology (NAT) assays for the detection of hepatitis C virus RNA is well known today, as many studies carried out in different European countries attest. The results of a previous study performed in Italy (J. Clin. Virol. 1 (2003) 83) by the Italian Society of Clinical Microbiology (AMCLI) showed that the use of external reference standards and of multicentre collaborative studies significantly improves laboratory performance for the qualitative evaluation of HCV RNA.

OBJECTIVES

the AMCLI organised a new study on the standardisation of both the qualitative and the quantitative evaluation of HCV RNA with NAT in order to improve the implementation of the diagnostic methods for HCV RNA detection.

STUDY DESIGN

seventeen diagnostic centres of major Italian Hospitals participated in this quality control study. The study consisted of testing three panels, each made up of 10 coded samples including negative and positive samples. Positive samples contained four levels of HCV RNA (genotype 1).

RESULTS AND CONCLUSION

Seven out of 510 qualitative results obtained were incorrect (1.4%), two false negative and five false positive. The results gave a sensitivity of 99.5% and a specificity of 95.8%. Regarding quantitative tests, the geometric mean (GM) and standard deviation (S.D.) could be calculated only for the three highest HCV RNA levels. The percentage of results within the range of GM +/- 0.5 log(10) varied from 91% to 100%. Some laboratories had some difficulty in the exact quantification of the lowest (3.00 log IU/ml) as well as of the highest viral levels (6.35 log IU/ml) values, very near to the limits of the dynamic range of the assays. The comparison of the results of this study with that previously carried out one confirms that a regular participation in external quality assessment (EQA) assures the achievement of a high proficiency level in the diagnosis of HCV infection.

Molecular and diagnostic clinical virology in real time

During the last decade, the application of both qualitative and quantitative nucleic acid detection techniques has had a major impact on diagnostics in clinical virology. Both signal and target amplification-based systems are currently used routinely in most if not all virology laboratories. However, commercial assays are only available for a very limited number of targets, and this has resulted in the development and introduction of assays developed in-house for most viral targets. With improved and automated nucleic acid sample isolation techniques, as well as real-time detection methods, a new generation of assays for most clinically important viruses is being developed. These technological improvements also make it possible to generate results with a very short turnaround time. As an example of a more individual-patient disease-management concept, we have introduced in our clinical setting the quantitative detection of Epstein-Barr virus (EBV) in T-cell-depleted allogeneic stem cell transplant patients. This has enabled us to develop models for pre-emptive anti-B-cell immunotherapy for EBV reactivation, and for reducing not only the incidence of EBV lymphoproliferative disease (EBV-LPD), but the virus-related mortality. It is now also feasible to introduce molecular testing for those viruses that can easily be detected using classical virological methods, such as culture techniques or antigen detection. Prospective studies are needed to evaluate the clinical importance of the additional positive samples detected. It should, however, be clear that a complete exchange of technology is unlikely to occur, and that complementary methods should stay operational, making possible the discovery of new viruses. Furthermore, the ability to characterise viruses more easily by sequencing opens new possibilities for epidemiological studies. There is also an urgent need, with regard to molecular diagnostic methods, for the introduction and use of standardised materials and participation in international quality control programmes. Finally, with the introduction of a universal internal control throughout the whole procedure, the accuracy of the results generated is warranted.

Reliability of nucleic acid amplification methods for detection of Chlamydia trachomatis in urine: results of the first international collaborative quality control study among 96 laboratories

The first European Quality Control Concerted Action study was organized to assess the ability of laboratories to detect Chlamydia trachomatis in a panel of urine samples by nucleic acid amplification tests (NATs). The panel consisted of lyophilized urine samples, including three negative, two strongly positive, and five weakly positive samples. Ninety-six laboratories in 22 countries participated with a total of 102 data sets. Of 204 strongly positive samples 199 (97.5%) were correctly reported, and of 506 weakly positive samples 466 (92.1%) were correctly reported. In 74 (72.5%) data sets correct results were reported on all samples, and 17 data sets (16.7%) showed either one false-negative or one false-positive result. In another 11 data sets, two or more incorrect results were reported, and two data sets reported a false-positive result on one negative sample. The Roche COBAS Amplicor test was performed in 44 (43%) data sets, the Abbott LCx assay was performed in 31 (30%) data sets, the Roche Amplicor manual assay was performed in 9 (9%) data sets, an in-house PCR was performed in 9 (9%) data sets, the Becton Dickinson ProbeTec ET assay was performed in 5 (4.9%) data sets, and the GenProbe TMA assay was performed in 4 (3.9%) data sets. The results of the Roche Amplicor manual (95.6% correct), COBAS Amplicor (97.0%), and Abbott LCx (94.8%) tests were comparable (P = 0.48). The results with the in-house PCR, BD ProbeTec ET, and GenProbe TMA tests were reported correctly in 88.6, 98, and 92.5% of the tests, respectively. Freeze-drying of clinical urine specimens proved to be a successful method for generating standardized, stable, and easy-to-transport samples for the detection of C. trachomatis by using NATs. Although the results, especially the specificity, for this proficiency panel were better than most quality control studies, sensitivity problems occurred frequently, underlining the need for good laboratory practice and reference reagents to monitor the performance of these assays.

Multicentre Italian Study Group (MISG) for the standardisation of hepatitis C virus (HCV) PCR

BACKGROUND

Several studies on standardisation of NAT assays for diagnosis of hepatitis C virus (HCV) infection have been carried out in European countries. In fact the widespreading use of nucleic acid amplification technology (NAT) in diagnostic centres for the evaluation of the HCV infection, requires the application of reference external standards to control laboratory performance; but up to date they are not routinely used.

OBJECTIVES

Fifteen diagnostic centres of major Italian Hospitals participated to a quality control study for the standardisation of polymerase chain reaction (PCR)-based HCV-RNA detection, organised by the Committee for the Study of Biotechnology (CoSBio) of the Italian Society of Clinical Microbiology (AMCLI). All the participant centres (PC) used commercial assays, automated or semi-automated.

STUDY DESIGN

The study was performed in four rounds. Altogether each centre received 14 reference negative and 22 reference positive sera. The range of copies number per ml of the reference positive sera was 10(4)-10(7).

RESULTS AND CONCLUSIONS

Considering the 540 samples tested, 4.54% of false negative (FN) and 4.28% of false positive (FP) results were reported. Thereafter the sensitivity and the specificity were 95.65 and 95.89%, respectively. The errors were distributed among seven out of the 15 PCs. The percentage of FP results was uniformly distributed in each shipment, whereas FN results emerged with the sera at lower HCV genome copies number. The analysis of the data obtained suggests that FP as well as FN results may be attributable to errors or to others problems of laboratories. To improve the performance of Italian, as well as of laboratories throughout the world, the use of external reference standards in multicentre collaborative studies will be required.

Progression of fibrosis in chronic hepatitis C

BACKGROUND & AIMS

Fibrosis is the hallmark of hepatic cirrhosis, worsening of which is probably the best surrogate marker for progression of chronic liver disease. We evaluated a large cohort of patients with chronic hepatitis C (CHC) using liver histology to assess the rate and predictors of progression of fibrosis.

METHODS

The cohort consisted of 123 patients with CHC who underwent 2 liver biopsies 4-212 months (mean, 44 months) apart without intervening treatment. Liver histology was graded using the histology activity index (score, 0-18) and fibrosis staged using a scoring system of 0 (no fibrosis) to 6 (cirrhosis).

RESULTS

Among 123 patients, 48 (39%) showed progression in fibrosis scores, 46 (37%) showed no change, and 29 (24%) showed improvement. Of those with worsening fibrosis, 75% had a 1-point increase and 25% a 2-point or greater increase in scores, and 9% showed progression to cirrhosis. The overall rate of progression was 0.12 fibrosis units per year, a rate that predicts progression to cirrhosis in 50 years if progression was linear. The rate of fibrosis progression was variable, and it was higher among older patients, those with higher serum alanine and aspartate aminotransferase levels, and those with the most extensive periportal necrosis on initial liver biopsy.

CONCLUSIONS

The best predictors of fibrosis progression in CHC are the extent of serum aminotransferase elevations and the degree of hepatocellular necrosis and inflammation on liver biopsy. These findings support the recommendation that patients with normal aminotransferase levels and mild liver histology can safely defer treatment.

Molecular diagnostics of viral hemorrhagic fevers

This review addresses the diagnostics of viral hemorrhagic fevers (VHFs). In the first part, an overview is given on classical methods of VHF diagnostics as well as novel molecular diagnostic tools. Currently available polymerase chain reaction (PCR) assays for diagnosis of VHF are summarized and discussed. In the second part, VHF diagnostics are described in particular for Lassa fever, yellow fever, and Crimean-Congo hemorrhagic fever, based on cases that were imported into or occurred within Europe. The third part is focussed on important differential diagnoses of VHF.

Quality control in nucleic acid testing--where do we stand?

Quality control has been playing an increasingly important role in the implementation of nucleic acid amplification techniques (NATs) for clinical diagnosis since the introduction of these methods in the early 1990s. Initial multicenter studies involving hepatitis B virus (HBV), hepatitis C virus (HCV), Mycobacterium tuberculosis, and human immunodeficiency virus type 1 (HIV-1) revealed serious problems in specificity (false-positive rates of ca. 40%) and sensitivity, large variations in quantitative results, and a plethora of units (largely not comparable between assays). The problem areas identified included the need for standardized reagents and common units, contamination control mechanisms, inhibition control mechanisms, genotype-independent detection and quantitation, facilitated nucleic acid isolation procedures, clinically relevant dynamic ranges, and internal run controls. Progress made in each of these areas will be discussed. In addition to the above-mentioned problem areas, the value of external quality control of existing and evolving NATs was recognized. To this end, the European Union Quality Control Concerted Action for Nucleic Acid Amplification in Diagnostic Virology was established in May 1998. During its three-and-a-half years of existence, a total of 14 proficiency panels containing 8-13 well-characterized, simulated clinical samples of various viral loads and genotypes were prepared for herpesviruses (herpes simplex virus, human cytomegalovirus), blood-borne viruses (HBV, HCV, HIV-1), enteroviruses, and Chlamydia trachomatis, distributed to up to 20 different countries, and tested by up to 97 different laboratories. The results show dramatic improvement in specificity (false-positive rates <3% for most panels), presumably due to a generally greater expertise of participating laboratories, more frequent use of enzymatic or mechanical contamination control mechanisms, and increased utilization of standardized reagents (commercial kits). However, considerable problems with sensitivity remain (false-negative rates up to 50%), reflecting the high detection limits of some commercial viral load kits still on the market as well as inadequate standardization of quantitation controls between assay systems. In conclusion, although considerable progress has been made, quality control of NATs in clinical diagnosis remains an ongoing challenge.

Clinical virology in real time

The ability to detect nucleic acids has had and still has a major impact on diagnostics in clinical virology. Both quantitative and qualitative techniques, whether signal or target amplification based systems, are currently used routinely in most if not all virology laboratories. Technological improvements, from automated sample isolation to real time amplification technology, have given the ability to develop and introduce systems for most viruses of clinical interest, and to obtain clinical relevant information needed for optimal antiviral treatment options. Both polymerase chain reaction (PCR) and nucleic acid sequence-based amplification (NASBA) can currently be used together with real time detection to generate results in a short turn-around time and to determine whether variants relevant for antiviral resistance are present. These new technologies enable the introduction of an individual patient disease management concept. Within our clinical setting, we have introduced this e.g. for quantitative detection of Epstein-Barr Virus (EBV) in T-dell depleted allogeneic stem cell transplant patients. This enabled us to develop models for pre-emptive anti B-cell immunotherapy for EBV reactivation, thereby effectively reducing not the incidence of EBV-lymphoproliferative disease but the virus related mortality. Furthermore, additional clinically relevant viruses can now easily be detected simultaneously. It also becomes more feasible to introduce molecular testing for those viruses that can easily be detected using classical virological methods, like culture techniques or antigen detection. Prospective studies are needed to evaluate the clinical importance of the additional positive samples detected. It should however be made clear that a complete exchange of technologies is unlikely to occur, and that some complementary technologies should stay operational enabling the discovery of new viruses. The implementation of these molecular diagnostic technologies furthermore warrants the use and introduction of standardized materials as well as participation in international quality control programs. Finally, the use of an internal control throughout the whole procedure not only ensures the accuracy of the results generated, but also is necessary to enable precise quantification of these results and to determine detection thresholds more accurately. Since so many targets do have clinical implications, laboratories might prefer to use universal internal controls before the in-house developed assays should be introduced in clinical virology.

External quality assessment program for qualitative and quantitative detection of hepatitis C virus RNA in diagnostic virology

To assess the performance of laboratories in detecting and quantifying hepatitis C virus (HCV) RNA levels in HCV-infected patients, we distributed two proficiency panels for qualitative and quantitative HCV RNA testing. The panels were designed by the European Union Quality Control Concerted Action, prepared by Boston Biomedica Inc., and distributed in May 1999 (panel 1) and February 2000 (panel 2). Each panel consisted of two negative samples and six positive samples, with HCV RNA target levels from 200 to 500,000 copies/ml. Panel 1 had four samples with at least 50,000 copies/ml, and panel 2 had two samples with at least 50,000 copies/ml. Fifty-seven laboratories submitted 45 qualitative and 35 quantitative data sets on panel 1, and 81 laboratories submitted 75 qualitative and 48 quantitative data sets on panel 2. In both panels, about two-thirds of the qualitative data sets and >90% of the quantitative data sets were obtained with commercial assays. With each panel, two data sets gave one false-positive result, corresponding to false-positivity rates of 1.3% and 0.8% for panel 1 and panel 2, respectively. Samples containing at least 50,000 copies/ml were found positive in 97% and 99% of the cases with panel 1 and panel 2, respectively. In contrast, the positive samples containing < or =5,000 copies/ml were reported positive in only 71% and 77% of the cases with panel 1 and panel 2, respectively. Adequate or better scores on qualitative results (all results correct or only the low-positive samples missed) were obtained in 84% (panel 1) and 80% (panel 2) of the data sets. In the analysis of quantitative results, 60% (panel 1) and 73% (panel 2) of the data sets obtained an adequate or better score (> or =80% of the positive results within the range of the geometric mean +/- 0.5 log(10)). Our results indicate that considerable improvements in molecular detection and quantitation of HCV have been achieved, particularly through the use of commercial assays. However, the lowest detection levels of many assays are still too high, and further standardization is still needed. Finally, this study underlines the importance of proficiency panels for monitoring the quality of diagnostic laboratories.

Sensitivity of HCV RNA and HIV RNA blood screening assays

BACKGROUND

The FDA requirement for sensitivity of viral NAT methods used in blood screening is a 95-percent detection limit of 100 copies per mL, whereas the NAT screening system should have a sensitivity of at least 5000 copies per mL per individual donation. According to the Common Technical Specifications of the European Directive 98/79/EC for in vitro diagnostics, viral standard dilutions (calibrated against the WHO standard) should be tested at least 24 times for a statistically valid assessment of the 95-percent detection limit.

STUDY DESIGN AND METHODS

Viral standard dilution panels (PeliCheck, VQC-CLB) were prepared for HCV RNA genotypes 1 and 3 and for HIV RNA genotypes B and E. In a multicenter study, 23 laboratories tested the panels all together in 8 to 91 test runs per NAT method.

RESULTS

The following 95-percent detection limits (and 95% CIs) were found on the HCV RNA genotype 1 reference panels (shown as geq/mL): Gen-Probe TMA, 85 (64-118); AmpliScreen, 126 (83-225); AmpliScreen with NucliSens Extractor, 21 (13-44); Amplicor with NucliSens Extractor, 69 (50-102), and Amplicor with Qiagen extraction technology, 144 (74-102). On HIV RNA genotype B dilution panels, the following 95-percent detection limits were found (shown as geq/mL): Gen-Probe TMA, 31 (20-52); AmpliScreen, 126 (67-311); AmpliScreen with NucliSens Extractor, 37 (23-69), and NucliSens QL assay, 123 (51-566). HIV RNA genotype E panels were detected with equal sensitivity as HIV RNA genotype B panels. In the Gen-Probe TMA assay, the 50-percent detection limits on HIV RNA type B and type E were 3.6 (2.6-5.0) and 3.9 (2.4-5.8) geq per mL, respectively. The HCV RNA genotype 1 and 3 standards were detected with equal sensitivity.

CONCLUSION

The differences in sensitivity between NAT assays can be explained by the input of isolated viral nucleic acid in the amplification reactions. The FDA requirements for sensitivity of NAT blood screening assays can be met by the Gen-probe TMA, as well as by the AmpliScreen assays, particularly when combined with the NucliSens Extractor.

European proficiency testing program for molecular detection and quantitation of hepatitis B virus DNA

External quality control of hepatitis B virus (HBV) DNA detection remains an important issue. This study reports and compares the results obtained from two different proficiency panels for both the qualitative and quantitative assessment of HBV DNA. The panels were designed by the European Union Quality Control Concerted Action, prepared by Boston Biomedica, Inc., and distributed in May 1999 (panel 1) and February 2000 (panel 2). Each contained two negative samples and six positive samples with 10(3) to 10(7) copies/ml (panel 1) or 10(3) to 2 x 10(6) copies of HBV DNA per ml (panel 2). For panel 1, 42 laboratories submitted 20 qualitative (all in-house PCRs) and 37 quantitative (87% commercial assays) data sets. For panel 2, 51 laboratories submitted 25 qualitative (all in-house PCRs) and 47 quantitative (94% commercial assays) data sets. Five data sets (8.8%) in panel 1 and two data sets (2.8%) in panel 2 contained totals of six and two false-positives, respectively, corresponding to false-positive result rates of 5.3% for panel 1 and 1.4% for panel 2. The false-negative result rates of 10.5% for panel 1 and 17.4% for panel 2 were dependent on the detection levels of the assays employed as well as panel composition. In the qualitative analysis of all data sets, 47.4% (panel 1) and 51.4% (panel 2) had all samples correct. An adequate or better score (all correct or only the weak-positive sample missed) was obtained with 77.2% of the panel 1 samples and 68.1% of the panel 2 samples. In the quantitative analysis, 57.1% (panel 1) and 42.6% (panel 2) of the data sets achieved an adequate or better score (positive results within the acceptable range of the geometric mean +/- 0.5 log(10) of all positive results). These results demonstrate that while the qualitative performance of HBV detection has considerably improved compared to that of a previously published HBV proficiency study, the detection levels of many commercial quantitative assays are still too high to allow adequate quantitation of all relevant clinical samples.

Quantitation of viral load using real-time amplification techniques

Real-time PCR amplification techniques are currently used to determine the viral load in clinical samples for an increasing number of targets. Real-time PCR reduces the time necessary to generate results after amplification. In-house developed PCR and nucleic acid sequence-based amplification (NASBA)-based systems combined with several detection strategies are being employed in a clinical diagnostic setting. The importance of these assays in disease management is still in an exploration phase. Although these technologies have the implicit capability of accurately measuring DNA and RNA in clinical samples, issues related to standardization and quality control must be resolved to enable routine implementation of these technologies in molecular diagnostics.

Prospective multicenter clinical evaluation of AMPLICOR and COBAS AMPLICOR hepatitis C virus tests

We conducted a multicenter clinical evaluation of the second versions of the manual AMPLICOR and the semiautomated COBAS AMPLICOR tests for hepatitis C virus (HCV) RNA (Roche Molecular Systems, Inc., Pleasanton, Calif.). The performance characteristics of these HCV RNA tests for diagnosis of active viral infection were determined by comparison to anti-HCV serological test results, alanine aminotransferase levels, and liver biopsy histology results. A total of 878 patients with clinical or biochemical evidence of liver disease were enrolled at four hepatology clinics. A total of 1,089 specimens (901 serum and 188 plasma) were tested with the AMPLICOR test. Sensitivity compared to serology was 93.1% for serum and 90.6% for plasma. The specificity was 97% for serum and 93.1% for plasma. A total of 1,084 specimens (896 serum and 188 plasma) were tested with the COBAS test. Sensitivities for serum and plasma were the same as with the AMPLICOR test. The specificity was 97.8% for serum and 96.6% for plasma. Of the 69 specimens with false-positive and false-negative AMPLICOR test results relative to those of serology, alternative primer set (APS) reverse transcription (RT)-PCR analysis showed that the AMPLICOR test provided the correct result relative to the specimens containing HCV RNA in 64 (92.7%) specimens. Similarly, 66 of 67 (98.5%) false-positive and false-negative COBAS test results were determined to be correct by APS RT-PCR analysis. There were no substantive differences in clinical performances between study sites, patient groups, specimen types, storage conditions (-20 to -80 degrees C versus 2 to 8 degrees C), or anticoagulants (EDTA versus acid citrate dextrose) for either test. Both tests showed >99% reproducibility within runs, within sites, and overall. We conclude that these tests can reliably detect the presence of HCV RNA, as evidence of active infection, in patients with clinical or biochemical evidence of liver disease.

Hepatitis C virus testing of plasma pools by nucleic acid amplification technology: external quality assessment

BACKGROUND AND OBJECTIVES

Since 1 July 1999, in accordance with European regulations, only batches of blood products obtained from plasma pools tested and found to be non-reactive for hepatitis C virus (HCV) RNA are being released. As monitoring the performance of manufacturers involved in plasma pool testing is important to ensure reliable amplification techniques, the Istituto Superiore di Sanità, as the Italian regulatory authority, organized an external quality assessment study.

MATERIALS AND METHODS

A reference HCV RNA panel calibrated in international units (IU) was sent to each participant to be tested according to the validated procedure they routinely used in plasma pool testing. The panel consisted of 20 coded samples, four of which were obtained from a negative plasma pool. The remaining 16 samples, prepared by diluting the national reference preparation (ISS HCV RNA 0498), represented four half-log dilution series, each consisting of four samples containing 100, 32, 10 and 3.2 IU/ml of HCV RNA.

RESULTS

The overall performance of the laboratories was very satisfactory. All laboratories correctly identified the negative samples. The 100- and 32-IU/ml samples were both detected in 98.4% of the assays, while the 10- and 3.2-IU/ml samples were detected in 73.4 and 50.0% of the assays, respectively. No substantial differences were observed between in-house procedures and commercial kits.

CONCLUSION

This external quality assessment study showed that manufacturers of blood products have reached a high level of proficiency that fully complies with the European Pharmacopoeia requirements. This finding is reassuring in the context of the safety of blood products.

Multicenter proficiency testing of nucleic acid amplification methods for the detection of enteroviruses

A multicenter study of molecular detection of enteroviruses was conducted using a proficiency panel. Of 70 data sets, 46 (66%) reported correct results for samples containing at least 1 50% infective dose per ml and for negative samples. Variation in performance between laboratories demonstrates the need for ongoing quality control.

Novel approach to reduce the hepatitis C virus (HCV) window period: clinical evaluation of a new enzyme-linked immunosorbent assay for HCV core antigen

The window period in hepatitis C virus (HCV) infection is still a major problem in ensuring blood safety. HCV RNA detection by nucleic acid amplification technology-based tests has contributed to reduce the infectivity of blood products, but it is expensive, time-consuming and affected by a high prevalence of false-positive results. The aim of this study was to assess the performance of a newly developed enzyme immunoassay for the detection of HCV core antigen and its suitability for use in the screening of blood units in order to identify infecting samples that do not contain specific antibodies. For evaluation of laboratory performance, different samples were selected: to evaluate specificity, we tested 2,586 sera from blood donors, 500 general population samples, and 58 "difficult sera". All samples were tested by two screening assays, and results were negative. To estimate clinical sensitivity, 103 HCV RNA-positive, anti-HCV-negative samples, 6 natural seroconversion panels, and 9 commercial seroconversion panels were tested. Intra- and interassay precision were determined on two HCV-RNA-positive, anti-HCV-negative sera. Seventeen (0.66%) blood donor samples, 2 (0.4%) general population samples, and 2 (3.44%) difficult sera were initially reactive; 3 sera were positive on repetition. These 21 samples tested by reverse transcription-PCR were negative. The clinical sensitivity calculated with seroconversion panels and seroconverted patient samples was very similar to PCR sensitivity: 95% of PCR-positive, antibody-negative samples contained detectable HCV antigen. Data on intra- and interassay precision showed dispersion indices with values of less than 10%. In conclusion, the HCV antigen assay showed high sensitivity and specificity and could become a useful means of improving the safety of blood and blood products.

Timing and interpretation of tests for diagnosing perinatally acquired hepatitis C virus infection

The diagnosis of hepatitis C virus (HCV) infection in children born to HCV-infected women is based on serologic assays and HCV RNA measurement by PCR. Interpretation of the results of these tests is hampered by uncertainty about the age distribution of loss of maternal antibody and the sensitivity and specificity of PCR at different ages. On the basis of findings from a recent vertical transmission study, we estimated the posttest probability of a child's being infected or uninfected under several test result scenarios. These estimates may assist clinicians in assessing the likelihood of infection in an individual child and in using the currently available assays cost effectively.

Clinical utility of viral quantification as a tool for disease monitoring

The possibility to detect viral DNA or RNA in a quantitative manner has already contributed significantly to the management and diagnosis of viral infections, as well as to the understanding of virus-host interactions. New developments in amplification techniques based on real-time detection, as well as automation of the whole process, will soon be introduced in a diagnostic laboratory setting, thereby enabling a rapid turnaround time to generate both quantitative and qualitative results. New guidelines for disease management, as well as extensive quality control and standardization programs must be introduced.

Incidence of hepatitis C virus RNA in anti-HCV negative plasma pools in Croatia

The risks of transmitting viral infection by blood and products derived from plasma have long been known and still remain an area of concern. Blood banks and transfusion centres are faced with the imminent introduction of nucleic acid amplification testing (NAT) of plasma pools as used by the plasma industry. In this paper, we show a part of our results of a validation study of an in-house method for routine polymerase chain reaction (PCR) screening for hepatitis C virus (HCV) RNA in plasma pools and the results of testing 2,718 anti-HCV negative plasma pools for the presence of HCV RNA. The European Committee for Proprietary Medical Products (CPMP) recommended that from 1 July 1999, only batches derived from plasma pools tested and found non-reactive for HCV RNA, using validated test methods of suitable sensitivity and specificity, should be batch released by authorities. The quality and efficiency of NAT detection of HCV RNA is among others influenced by the efficacy of RNA isolation, the primer selection and the use of control samples. Using modern molecular biology techniques (sensitive and specific in-house amplification methods for detection of HCV RNA and automated sequencing), we analysed samples of plasma pools from different Croatian transfusion centres. By detection of HCV RNA in an NIBSC working reagent (genotype 3) and a Pelispy HCV RNA run control (genotype 1) we determined a high reproducibility and sensitivity (below 100 International Units (IU)/ml) for our in-house method. By direct sequencing PCR cDNAs we proved the specificity of the test system and the possibility of determining the HCV genotype when the method was used for PCR screening of HCV RNA in single donations. Of 2,718 anti-HCV negative plasma pools we have found that 2.1$ were HCV RNA positive. Results of our investigation confirm the necessity of testing HCV RNA in plasma pools to further increase the safety of human plasma-derived drugs.

Validation and standardisation of nucleic acid amplification technology (NAT) assays for the detection of viral contamination of blood and blood products

Standardisation of NAT assays is necessary before the introduction of such assays for routine screening of blood and blood products for viral contaminants such as HBV, HCV, and HIV-1. Standardisation can be achieved by the use of well-characterised reference materials (working reagents) to validate each assay run. Working reagents for HCV, HIV-1, HBV, HAV, and human parvovirus B19 have been established by the NIBSC. Such reagents and reference panels are also available from other official medicinal control laboratories and commercial organisations. However, the nucleic acid content of these reagents are expressed in many different units, e. g. genome equivalents/ml, copies/ml, PCR detectable units/ml, making comparisons of results from laboratories using different reagents difficult. The establishment of internationally accepted standards against which all working reagents could be calibrated, using a common standard unit of measurement, IU, would overcome this major problem. The first International Standard for HCV RNA assays was established in 1997. This reagent, 96/790, is a lyophilised preparation of a genotype 1 isolate and the concentration of the standard is 10(5) IU/ml. Two further International Standards have since been established; for HIV-1 and HBV, containing 10(5) IU/ml and 10(6) IU/ml respectively. The establishment of the HCV International Standard has been critical in the introduction of mandatory testing. Since 1st July 1999, all batches of blood products marketed in Europe have to be prepared from plasma pools tested and found non-reactive for HCV RNA using a validated assay which can detect a sample containing 100 IU/ml of HCV RNA. In Germany, screening of blood donations for HCV RNA by NAT has been mandatory since 1st April 1999. The minimum sensitivity of assays should be 5000 IU/ml for a single donation.

Testing of individual blood donations for HCV RNA reduces the residual risk of transfusion-transmitted HCV infection

BACKGROUND

To allow cost-effective RNA testing with NAT techniques, the national authorities of several countries have planned or already introduced tests of mixed specimens, that is, plasma pools.

STUDY DESIGN AND METHODS

High-throughput extraction, amplification, and detection of HCV RNA from individual blood donations were optimized and validated. The feasibility of the method and the frequency of anti-HCV-negative, HCV RNA-positive donations were determined in a prospective study of 27,745 allogeneic and 792 autologous individual donations.

RESULTS

The 50- and 95-percent detection limits of the method were determined at 44 IU per mL and 162 IU per mL, respectively (World Health Organization HCV reference material). When 201 HCV RNA-positive sera were taken as a reference, the sensitivity was 97.5 percent. The assay specificity was determined at 99.77 percent. During a 20-month period, two seronegative blood donors tested positive in HCV PCR. The viral load of these donations was 6 x 10(6) and 3 x 10(7) copies per mL, respectively. Thus, the yield of HCV RNA testing in this study was 7. 63 per 100,000 screened donations (95% CI, 1.25-22.07). In both PCR-positive donors, seroconversion was found in subsequent blood samples.

CONCLUSION

This study compares the feasibility of single-donation HCV RNA screening, with the detection of a relatively high percentage of window-phase donations, to data reported from groups using HCV RNA testing of plasma pools. The relative yield of NAT of individual donations versus minipools should be directly investigated in the near future.

Quantification of viral load: clinical relevance for human immunodeficiency virus, hepatitis B virus and hepatitis C virus infection

Quantitative determination of viral load using nucleic acid amplification techniques represents the most accurate prognostic marker for human immunodeficiency virus type 1 (HIV-1) infection, independently of CD4+ cell count. Overall, the different methods for HIV-1 RNA determination (RT-PCR, nucleic acid sequence-based amplification, branched DNA) show a good reproducibility (0.5 log), however for low copy numbers and in HIV-1-infected children the variability may exceed 0.7 log. In non-HIV-1 subtype B infections the copy number is underestimated. While serology permits an accurate follow-up of hepatitis B virus (HBV) infection, HBV DNA quantification is used for monitoring of antiviral therapy, determination of infectiosity and in combination with serological markers for the resolution of unusual profiles, i.e. isolated anti-HBc reactivity. The prognostic relevance of hepatitis C virus (HCV) RNA determination is of limited value for the long-term prognosis of chronic hepatitis C, however the viral load may predict the outcome of antiviral therapy. Genetic diversity represents a challenge for HCV RNA quantification.

Evaluation of automated nucleic acid extraction devices for application in HCV NAT

BACKGROUND

To further improve the safety of the blood supply, various national blood transfusion organizations presently use or are in the process of implementing routine HCV NAT in minipools. According to the Committee for Proprietary Medicinal Products (CPMP) of the European Union, the HCV NAT detection limit of the assay should be 100 IU per mL (270 geq/mL) for testing initial plasma pools. Paul Ehrlich Institute (PEI) regulations stipulate that 5000 IU per mL (13,500 geq/mL) must be detected to calculate the amount contributed by individual donations composing the minipool. The sensitivity for HCV RNA extraction achieved by three commercially available laboratory kits was compared.

STUDY DESIGN AND METHODS

Nucleic acids from 1-in-3 serial dilutions of an HCV RNA run control (Pelispy, CLB) were extracted with three kits (Cobas Amplicor, Roche Diagnostic Systems; BioRobot 9604, Qiagen; and NucliSens Extractor, Organon Teknika). HCV PCR of all extracts was performed using a second-generation Cobas Amplicor HCV test and the Cobas Amplicor analyzer.

RESULTS

The manual Cobas Amplicor, the BioRobot 9604, and the NucliSens Extractor setups allow a 95-percent HCV RNA detection limit of 129, 82, and 12 geq per mL, respectively. The maximal pool size for the manual Cobas Amplicor, the BioRobot 9604, and the NucliSens Extractor kits that would still meet the PEI criteria for HCV NAT in minipools was calculated at 104, 164, and 1125 donations, respectively.

CONCLUSION

All three HCV NAT kits evaluated meet the criteria set by CPMP and PEI. The highest sensitivity for HCV NAT screening can be achieved with the high-volume NucliSens Extractor method in combination with the Cobas Amplicor HCV v2.0 test on the Cobas Amplicor analyzer.

Performance of the COBAS AMPLICOR HCV MONITOR test, version 2.0, an automated reverse transcription-PCR quantitative system for hepatitis C virus load determination

A clinical evaluation of an automated quantitative PCR assay, the COBAS AMPLICOR HCV MONITOR test, version 2.0 (v2.0), was carried out to assess the performance of this test in comparison with that of the previous, manual version, the AMPLICOR HCV MONITOR test, and with that of nested PCR. Serial dilutions of serum samples infected with genotype 1b, 2a, or 3, as well as synthetic RNA transcripts and serum samples derived from 87 patients with chronic hepatitis C and infected with genotype 1a, 1b, 2a, 2b, 3a, 3b, 4, or 5, were analyzed to determine the ability of the system to efficiently quantify various hepatitis C virus (HCV) genotypes. These experiments showed that the COBAS AMPLICOR HCV MONITOR test, v2.0, has mean intra-assay, interassay, and interoperator coefficients of variation that range from 22 to 34.5% and a 3-logarithm dynamic range, which spans from 10(3) to 10(6) copies/ml. Compared to the previous, manual version of the test, the COBAS AMPLICOR HCV MONITOR test, v2.0, showed an improved efficacy for all genotypes, especially genotypes 2, 3, and 4, whose estimated concentrations were on average 1 logarithm higher. When used to monitor patients under treatment, however, both versions showed the same patterns of viremia, indicating that the COBAS AMPLICOR HCV MONITOR test, v2.0, and the AMPLICOR HCV MONITOR test were equally effective at detecting relative viremia changes in serial samples. As expected, the automated test was less sensitive than nested PCR; among specimens from a cohort of patients treated with interferon, nested PCR identified three more viremic specimens, which probably contained very low concentrations of HCV RNA.

A multicenter study evaluation of the digene hybrid capture II signal amplification technique for detection of hepatitis B virus DNA in serum samples and testing of EUROHEP standards

We have evaluated the new Digene Hybrid Capture II HBV DNA Test (HCII HBV), which is a 96-well microtiter plate-based signal amplification assay. This test uses hybrid capture technology that specifically detects RNA-DNA hybrids. HCII HBV is able to quantify hepatitis B virus (HBV) DNA at between 1.4 x 10(5) and 1.7 x 10(9) HBV copies per ml in a standard format. By using a modified sample preparation method, which allows the input of 30-fold more serum for an ultrasensitive format, the sensitivity of the assay can be increased reproducibly to approximately 8,000 copies of HBV per ml. By using a combination of these two formats, the assay can quantify over a total range of 6 logs. In our multicenter evaluation study, the mean laboratory-to-laboratory coefficients of variation were 22, 7, and 12% at the three sites, respectively, with a combined specificity of 98.4%. The linearities of both the standard test and the ultrasensitive test were excellent, with Spearman correlation coefficients of 0.997 and 0.999, respectively. Furthermore, the intra-assay reproducibility for the standard assay gave coefficients of variation of from 13 to 33, 9 to 21, and 3 to 8% at the three sites, respectively. HCII HBV was shown to be genotype independent when the EUROHEP standards for genotypes A and D were used. This assay allows the accurate measurement of HBV DNA levels in serum and can be clinically used for the monitoring of responses to antiviral agents for patients chronically infected with HBV.

Evaluation of automated RNA-extraction technology and a qualitative HCV assay for sensitivity and detection of HCV RNA in pool-screening systems

BACKGROUND

The objective of this study was the evaluation of NAT technology for the detection of HCV RNA in plasma pools according to the recommendations of the Paul Ehrlich Institute (5000 IU/mL/donation) and the Committee for Proprietary Medical Products (100 IU/mL/manufacturing pool).

STUDY DESIGN AND METHODS

Serial dilutions of both the EUROHEP standard (3,800 genome equivalents [geq]/mL; HCV genotype 1) and the World Health Organization (WHO) international standard (100,000 IU/mL; HCV genotype 1) were made in S/D plasma (ESPEP plasma, OctaPharma), which was nonreactive in serologic tests. Serial dilutions of plasma (2 mL) were used for extraction of HCV RNA with an automated version of a nucleic acid isolation method (NucliSens Extractor, Organon Teknika). HCV RNA was co-extracted from 2 mL of plasma, together with 84 copies of an in vitro-synthesized single-strand RNA serving as internal extraction control (IC) to monitor the efficiency of extraction and PCR. Amplification and detection of both HCV RNA and IC RNA were performed with an automated PCR system and a qualitative HCV assay (COBAS Amplicor 2.0 HCV, Roche Diagnostics).

RESULTS

A cutoff value of 16 geq per mL (10/10 runs [100% hit rate]) was found by using the EUROHEP standard, whereas the WHO international standard had a cutoff value of approximately 12 IU per mL (10/10 runs [100% hit rate]). The IC had a cutoff value of approximately 17.5 copies per mL (6/6 runs [100% hit rate]). Forty-two copies per mL of IC RNA were found in 282 of 284 runs (99% hit rate). The negative controls (ESDEP plasma) were negative in all experiments. Experiments with pool sizes of 12, 24, 48, and 96 using serial dilutions of the WHO international standard revealed a cutoff value of 8 IU per mL (100% hit rate). The EUROHEP standard and the WHO international standard were detected with a 50 percent detection endpoint of 5.2 geq per mL and 1.5 IU per mL, respectively.

CONCLUSION

This test system (NucliSens Extractor, and the COBAS Amplicor 2.0 HCV assay) revealed a high sensitivity for HCV RNA; considering the proposed requirements for sensitivity of NAT assays for the detection of HCV RNA in donor plasma, pool sizes of about 400 donors are possible. These endpoint results indicated that 1 IU is equal to about 3.4 geq.

Classical swine fever virus: a ring test to evaluate RT-PCR detection methods

Six laboratories participated in an exercise to compare the sensitivity and specificity of RT-PCR tests for the detection of classical swine fever virus (CSFV). Two sets of coded samples were prepared by serial dilution of positive samples and then distributed to each of the laboratories. One set comprised 34 samples of random primed cDNA. These had been synthesised from viral RNA representative of seven different genetic subtypes of CSFV. The other set comprised 40 clinical samples containing tonsil, spleen, whole blood or serum from a pig that had been experimentally infected with CSFV. Each laboratory tested the samples using one or more PCR/RT-PCR tests that they were accustomed to using. The methods and results of the laboratories were compared with one another. The RT-PCR results obtained from testing the clinical samples were also compared with those obtained by virus isolation and antigen ELISA.ELISA. Both RT-PCR and RT-nested PCR appeared to give some false positive results. Several of the PCR tests appear suitable in terms of specificity and sensitivity. Further trials are necessary to compare results when the same test is performed by different laboratories, and to show that improved control procedures can eliminate problems due to false positive reactions.A limited comparison of extraction and reverse transcription procedures showed similar results in each of three participating laboratories, even though the methods were not standardised.

Performance of an automated system for quantification of hepatitis C virus RNA

The Amplicor HCV Monitor test for quantitative determination of serum or plasma hepatitis C virus (HCV) RNA was modified recently and introduced onto the Cobas Amplicor instrument to automate fully amplification, detection and calculation of results. This new version (v2.0) was evaluated in a routine diagnostic laboratory. The sensitivity and reproducibility were assessed on well-characterized panels (Eurohep) and clinical samples. HCV RNA levels measured by the v2.0 Monitor test were about 1log(10) higher than those detected by the previous version test, and genotypes 1 and 3 were quantified with equal sensitivity. Within the linear dynamic range of 10(3) to 10(6) copies/ml, the coefficients of variation for both intra- and inter-assay reproducibility ranged from 1.9 to 2.95%. This test system was found to be a reliable and labor saving assay for the quantification of HCV RNA.

Diagnostic tests for hepatitis C

Two categories of virological assays are in practice used for the diagnosis and management of hepatitis C virus (HCV) infection, including serological and molecular biology-based assays. Serological assays include: screening tests based on enzyme immunoassays (EIAs); supplemental "analytical" assays based on immunoblot testing; and serological assays detecting genotype-specific antibodies for the serological determination of HCV genotype, so-called "serotyping" assays. Molecular assays include: qualitative assays, detecting HCV RNA in body fluids; quantitative assays measuring HCV viral load, a parameter that estimates the level of HCV replication in the liver; and tests analyzing the sequence of HCV genomes (genotyping assays).

Hepatitis C virus transmission by a blood donation negative in nucleic acid amplification tests for viral RNA

Hepatitis C virus (HCV) was transmitted by transfusion of a platelet concentrate made from an anti-HCV and HCV-PCR-negative blood donation. Even a negative nucleic acid amplification test cannot completely prevent transmission of HCV.

Standardization: a progress report

The introduction of nucleic acid amplification technology (NAT) assays for the detection of viral contamination of blood and blood products requires the availability of well-characterized reference reagents. Working reagents for hepatitis C virus RNA, hepatitis B virus DNA, HIV-1 RNA and human parvovirus B19 DNA have been established at NIBSC and at many other laboratories (both official medicinal control laboratories and commercial laboratories). However, as these reagents have been characterised independently, it is difficult to compare results from assays using different working reagents. Recently, a WHO International Standard was established for HCV RNA NAT assays. This standard has been calibrated in International Units (IU) and provides a common standard against which all working reagents can be calibrated. Collaborative studies to characterise two further candidate International Standards for HBV DNA and HIV-1 RNA NAT assays have been completed.

Characterization of the quantitative HCV NASBA assay

A quantitative nucleic acid sequence-based amplification assay (NASBA-QT) for detection of hepatitis C virus RNA (HCV-RNA) was evaluated and compared with the HCV branched-DNA (bDNA) assay (Chiron Corporation) and the HCV MONITOR assay (Roche Diagnostic Systems). For this evaluation five panels were designed: (1) serial dilutions of genotype 1b in-vitro HCV-RNA; (2) standards of in-vitro HCV-RNA genotypes 1a, 1b, 2, 3, 4, and 5; (3) a proficiency panel consisting of 12 HCV-RNA positive plasma samples of different genotypes and HCV-RNA concentrations and a genotype 1a and 1b 3-fold dilution series; (4) a panel of 67 HCV-RNA positive plasma samples obtained from patients with HCV infection and (5) an HCV-RNA positive control sample, diluted 50-fold in 25 different HCV-RNA negative plasma samples. The quantitative detection limit was found to be 10(3) copies per 100 microl and the qualitative detection limit 10(2.3) per 100 microl. The amplification efficiency was independent of the plasma matrix, but dependent on the HCV genotype. The HCV NASBA-QT assay was more than 10 times as sensitive as the bDNA assay while the quantitative results of both assays were highly concordant. The HCV NASBA-QT assay was comparable in sensitivity with the HCV MONITOR assay, but the HCV MONITOR assay yielded consistently lower values. It is concluded that the HCV NASBA-QT assay is a reliable assay for quantitative HCV-RNA detection in various settings.

Introduction of the gene amplification technique to decrease the risk of hepatitis C virus transmission by plasma products

The viral safety of plasma-derived products with respect to hepatitis C virus (HCV) is assured by selection of donors, screening of individual donations for antibodies to HCV and the incorporation of effective viral inactivation-removal steps into manufacturing processes. As antibody screening of single donations is not sufficient to completely eliminate HCV RNA positive plasmas from plasma pools, testing for HCV RNA by gene amplification techniques may be necessary to identify positive donations. Using modern molecular biology techniques, we developed a specific, sensitive and reproducible method for routine PCR screening for HCV RNA in plasma pools.

Establishment of the first international standard for nucleic acid amplification technology (NAT) assays for HCV RNA. WHO Collaborative Study Group

BACKGROUND AND OBJECTIVES

The aims of this study were the establishment of a WHO International standard for HCV RNA for nucleic acid amplification technology (NAT) assays and the determination of the HCV RNA content of the candidate standard.

MATERIALS AND METHODS

Twenty-two laboratories evaluated three candidate materials (two lyophilised, AA and BB, which were derived from the same source and one a liquid preparation, CC). All samples were HCV genotype 1 with a concentration of approximately 10(5) genome equivalents/ml. The methods used included the Roche Amplicor assay (version 1), Chiron Quantiplex (bDNA) assay, Organon Teknika NASBA assay, Transcription Mediated assay and various in-house assays, using single or nested primers.

RESULTS

There was reasonable agreement between the overall mean NAT detectable units/ml obtained by the different assays except for some of the in-house assays using single primers which gave substantially lower estimates. These titres were 5.0 log10 for samples AA and BB and 4.6 log10 for sample CC.

CONCLUSIONS

Sample AA was accepted as the candidate standard and assigned a titre of 10(5) international units (IU)/ml. The International Standard consists of a batch of vials each containing 50,000 IU/vial. Preliminary studies indicated that the material is stable at +4 degrees C and +20 degrees C for up to 200 days.

Hepatitis viruses and the safety of blood donations

Since the beginning of blood transfusions concomitant transmission of viral hepatitis has been a frequent and serious side-effect. A first measure to reduce the frequency of transmission was the screening of blood donors for elevated levels of liver enzymes in the blood, which was introduced in Germany in the 1960s, but not in most other countries. After the discovery of hepatitis B virus (HBV), donors in all countries have been screened since the 1970s for its surface antigen (HBsAg). When it was realized that there was at least one other type of virus that was even more frequently transmitted, screening for liver enzymes and HBV antibodies (anti-HBc) was introduced as a surrogate marker in most, but not all, countries in the 1980s. Furthermore, donors at risk for parenterally transmitted viruses were excluded. The discovery of the hepatitis C virus (HCV) genome and the development of sensitive anti-HCV assays has meant that reliable detection of persistently infected HCV carriers has been possible since 1991. Recently infected donors, however, are infectious for several weeks or months before anti-HCV is detectable. Therefore, starting in April 1999 all donations in Germany have to be tested, by nucleic acid amplification tests, for the presence of HCV RNA, although preliminary experience shows that such recent HCV infections are very rare. Newly detected viruses, named GBV-C or HGV and TTV, have been detected in patients with non-A-E post-transfusion hepatitis, but their association with the disease seems to be coincidental. These viruses cause persistent viraemia and are quite prevalent world-wide, but do not cause any known disease. At present, transfusion-transmitted hepatitis has been virtually eliminated, and any improvement in safety will be very small and will require huge costs.

Multicenter quality assessment of PCR methods for detection of enteroviruses

We conducted a multicenter evaluation of commercial and in-house PCR methods for the detection of enteroviruses. Three coded panels of test and control RNA samples, artificial clinical specimens, and representative enterovirus serotypes were used to assess amplification methods, RNA extraction methods, and reactivities with different enterovirus serotypes. Despite several differences between PCR methods, there was good agreement, although some variation in sensitivity was observed. Most PCR methods were able to detect enterovirus RNA derived from 0.01 50% tissue culture infective dose (TCID50) and were able to detect at least 1 TCID50 of enterovirus in cerebrospinal fluid, stool, or throat swab specimens. Most were also able to detect a wide range of enterovirus serotypes, although serotypic identification was not possible. Some laboratories experienced false-positive results due to PCR contamination, which appeared to result mainly from cross-contamination of specimens during RNA extraction. Provided that this problem is overcome, these PCR methods will prove to be a sensitive and rapid alternative to cell culture for the diagnosis of enterovirus infection.