Correlation between detection of antibodies against hepatitis C virus in oral fluid and hepatitis C virus RNA in serum

Reported here are the results of a study designed to determine the correlation between hepatitis C virus (HCV) RNA positivity in serum and the detection of antibodies against HCV in oral fluid by testing paired serum/oral fluid samples. For the 85 serum samples found positive for antibodies against HCV, using a screening assay and a confirmation assay, 70 of the corresponding oral fluid samples tested positive for HCV antibodies using a previously modified screening assay. For 52 of the 59 serum samples found positive for HCV RNA, the corresponding oral fluid samples also tested seropositive for HCV, while 18 of the 26 serum samples that were negative for HCV RNA had corresponding oral fluid samples that tested seropositive for HCV. For the control group of 54 serum samples that were negative for HCV antibodies, all of the corresponding oral fluid samples were also negative for HCV antibodies, while 53 of the serum samples tested negative for HCV RNA. These results suggest that HCV antibody detection in oral fluid has a slightly higher sensitivity when used to test patients whose serum samples are positive for HCV RNA (chi-square test, p=0.035; Mid-P exact, p=0.049).     

A cost-effective algorithm for the diagnosis of Hepatitis C virus infection and prediction of HCV viremia in Cameroon

Conventional tests for antibody to Hepatitis C virus (HCV) and HCV RNA require considerable time before results are available, remain very expensive and are not adapted to many sub-Saharan African countries where HCV is endemic. The aim of this study was to evaluate the accuracy of an algorithm consisting of two HCV rapid tests to diagnose and predict HCV viremia in patients in Cameroon. Three hundred and twenty nine plasma samples were screened by two HCV rapid tests (ImmunoComb II HCV, PBS Orgenics and Hexagon HCV, Human). Previous evaluation of these samples for HCV antibodies (anti-HCV) by conventional third generation ELISA, considered as a reference test, indicated that 168 were anti-HCV negative and 161 positive. Among the 161 anti-HCV positive plasma, 114 (71%) were HCV RNA-positive by RT-PCR assay. The ImmunoComb II HCV test provided the more sensitive detection of anti-HCV (sensitivity: 99.4% with a 95% CI = 96-100%). Surprisingly, the second HCV rapid test, Hexagon HCV, showed a high capacity to identify non-viremic subjects amongst anti-HCV positive cases (93.6% [95% CI: 82-99%]). These results suggest an algorithm using ImmunoComb II HCV as a first test to screen anti-HCV positive subjects, and Hexagon HCV as a second test to discriminate between viremic and non-viremic HCV seropositive subjects.     

Sensitivity of a modified version of the ARCHITECT Anti-HCV test in detecting samples with immunoblot-confirmed, low-level antibody to hepatitis C virus.

BACKGROUND AND OBJECTIVES: Compliance with current regulations regarding the prevention of hepatitis C virus (HCV) transmission in the blood transfusion setting requires the use of sensitive assays for HCV antibody (anti-HCV) detection, which should, ideally, identify any donor having had prior contact with the virus. Therefore, low-level anti-HCV positive blood units should be detected by the screening assays, even those reflecting a past and resolved infection. To assess the sensitivity of two versions of an automated chemiluminescent microparticle immunoassay (CMIA) for anti-HCV screening (ARCHITECT Anti-HCV), 113 single serum samples containing low levels of anti-HCV, assessed by two immunoblot tests, were selected from 3686 samples received for confirmation of HCV infection by a reference laboratory over a 2-year period. MATERIALS AND METHODS: The panel included 17 samples with HCV RNA detected by the polymerase chain reaction (PCR) and 96 PCR negative samples with either positive or indeterminate (anti-Core and anti-NS3 alone) results by immunoblot. RESULTS: All but 13 specimens (100/113, 88.5%) were detected by the current version of the ARCHITECT Anti-HCV assay and 10 additional samples (110/113, 97.3%) tested positive in a modified version of the test. CONCLUSION: The results showed that the modification introduced in the ARCHITECT Anti-HCV assay achieves a significant sensitivity improvement including samples with low-level anti-HCV which are either PCR positive or negative.     

Detection of hepatitis C virus antibodies in oral fluid specimens for prevalence studies

Within the framework of hepatitis C virus (HCV) prevalence monitoring, we evaluated oral fluid (OF), which is richer in IgG than whole saliva, as a possible alternative to serum for the detection of HCV antibodies. Paired OF and serum samples were collected from 90 individuals, including 45 HCV-positives and 45 HCV-negatives. The detection of HCV antibodies in both serum and OF was performed using the Ortho HCV 3.0 SAVe enzyme-linked immunosorbent assay (ELISA) (Ortho-Clinical Diagnostics, Inc., Raritan, NJ), but a modified, more sensitive protocol was used to process OF. The sensitivity and specificity of this assay were 86.67% (95% confidence interval (CI): 72.51–94.46%) and 100% (95% CI: 90.20–99.80%) in OF and 100% in serum. The correlation obtained between both types of clinical specimens was excellent (k: 0.87, 95% CI: 0.66–1.07). However, the negative predictive value (NPV) of the assay in OF decreased with the prevalence of HCV infection in the population studied. Our results suggest that the modified Ortho HCV 3.0 SAVe ELISA is suitable for the detection of HCV antibodies in OF for epidemiological studies. Using this assay, we observed an unadjusted anti-HCV prevalence of 78.6% among a population of intravenous drug users; when adjusted to account for assay sensitivity, this prevalence may be closer to 90%.     

Hepatitis C virus infection among pregnant women in Yaounde,Cameroon: prevalence,viremia, and genotypes

Central Africa is considered to be an area of high endemic hepatitis C infection. To determine the prevalence of anti-HCV antibodies, HCV RNA, and the genotype distribution in Cameroon, 1,494 pregnant women attending antenatal care units in Yaounde, Cameroon were screened for HCV infection. Anti-HCV antibodies were detected with a 3rd generation ELISA (Monolisa anti-HCV plus version 2, BioRad, Richmond, CA). All anti-HCV antibody-positive sera were then tested with another 3rd generation ELISA (AxSYM) HCV version 3, Abbott Laboratories, Abbott Park, IL) and subsequently for HCV RNA (Amplicor HCV, Roche Diagnostics, Basel, Switzerland). Genotype was determined by phylogenetic analysis of the NS5b gene. Seventy-three pregnant women were found to be anti-HCV antibody positive by the first ELISA, but only 28 were anti-HCV positive by both ELISA. The prevalence of anti-HCV antibodies was thus 1.9% (28/1,494) (95% CI: 1.3-2.7%). 21/28 (75%) of the positive samples by both ELISA were HCV RNA positive. The 45 samples that were HCV antibody negative by the second ELISA were also HCV RNA negative. The HCV subtypes identified were 1a (24%), 2f (38%) and 4f (38%). In contrast to previous studies, anti-HCV antibodies were rare among pregnant women in Cameroon. The percentage of HCV seropositive pregnant women who had circulating HCV RNA was similar to that observed in Europe. Several HCV genotypes were found in Cameroon.     

Twenty-four mini-pool HCV RNA screening in a routine clinical virology laboratory setting: a six-year prospective study

The usefulness of combined anti-HCV and 24 mini-pool HCV RNA screening strategy was re-evaluated after a six-year continuous routine use in a clinical virology laboratory, at which more than half of newly diagnosed hepatitis C patients are intravenous drug users. Pools of 24 samples were prepared from 20,448 anti-HCV negative serum samples and tested using an automated commercial PCR assay with a lower limit of detection of 50 IU/ml. After detection of anti-HCV negative/HCV RNA positive patients, responsible physicians provided follow-up samples. Thirty-eight (0.19%) anti-HCV negative/HCV RNA positive samples from 30 patients (28 intravenous drug users) were detected. Follow-up samples were available for 27/30 patients. Twenty, six and one patient seroconverted in the second, third and fourth available samples, respectively. The interval between the first HCV RNA positive and the first available anti-HCV positive sample was 17-517 days. The costs of detecting a single anti-HCV negative/HCV RNA positive patient were 1227 Euros. Combined anti-HCV and 24 mini-pool HCV RNA screening is a useful and cost effective strategy, not only in blood-transfusion settings but also in a routine clinical virology laboratory, at which a significant proportion of the tested population belongs to a high-risk population.     

Use of combined detection of hepatitis C virus core antigen and antibodies to reduce the serological window-phase

OBJECTIVES: In this study, we aimed at evaluating the performances of a combined assay for the detection of hepatitis C virus core antigen and antibodies and comparing this test with conventional third generation Elisa. MATERIAL AND METHODS: Two hundred forty-one samples were included in this study and tested by Monolisa HCV Ag-Ab ULTRA, Biorad and compared to Monolisa Anti-HCV Plus. A comparative study was performed on a HCV seroconversion panel (Monolisa anti-HCV Plus, Biorad; Innotest HCV Ab IV, Innogenetics and Murex anti-HCV, Abbott). False positive samples were detected with western blot assay (INNO-LIA HCV Ab III, Innogenetics). Two anti-HCV negative haemodialysis patients with rise in ALT have been tested for RNA detection (Amplicor v2.0, Roche). RESULTS: Results obtained with Biorad Ag-Ab were in agreement with third generation ELISA on HCV seroconversion panel. From anti-HCV negative patients, four samples were found low positive with HCV Ag-Ab. Two anti-HCV negative haemodialysis patients/HCV RNA positive were also negative with HCV Ag-Ab and 13 low positive samples with Biorad Ab were found negative with Ag-Ab. CONCLUSION: The HCV Ag-Ab assay has a high specificity and sensitivity comparatively to conventional ELISA; but in our study we don't prove the reduction of the "serologic window" for detection of anti-HCV antibodies.     

Evaluation of a commercial rubella IgM assay for use on oral fluid samples for diagnosis and surveillance of congenital rubella syndrome and postnatal rubella.

BACKGROUND: Clinical diagnosis (surveillance) of rubella is unreliable and laboratory confirmation is essential. Detection of virus specific IgM in serum is the most commonly used method. However, the use of serum necessitates the drawing of blood, either through venipuncture or finger/heel prick, which can be difficult in young babies. Oral fluid samples have proved useful as an alternative, less invasive sample for virus specific IgM detection however until recently no commercial rubella IgM tests were available, restricting the usefulness of this approach. OBJECTIVES: To evaluate the performance of the Microimmune Rubella IgM capture EIA using oral fluid samples from outbreaks as well as in cases of suspected congenital rubella syndrome (CRS). STUDY DESIGN: Paired serum and oral fluids were collected from cases during a rubella outbreak in three provinces in Turkey. Matched serum and oral fluid samples were collected from children with suspected CRS in an active surveillance programme at the Aravind Eye Hospital in South India. Serum samples were collected as part of the measles surveillance programme in Ethiopia. RESULTS: On serum samples the sensitivity and specificity of the Microimmune Rubella IgM capture EIA compared to Behring Enzygnost rubella IgM test was 96.9% (62/64; 95% CI 94.2-100%) and 100% (53/53; 95% CI 93.2-100%). On oral fluids compared to matched Behring results on serum the sensitivity was 95.5% (42/44; 95% CI 84.5-99.4%). The sensitivity and specificity of Microimmune Rubella IgM capture EIA on oral fluids from suspected CRS cases compared to serum results using Behring Enzygnost IgM assay was 100% (95% CI 84.5-100%) and 100% (95% CI 95.8-100.0%) respectively. CONCLUSION: Microimmune Rubella IgM capture EIA has adequate performance for diagnosis and surveillance of rubella in outbreak using either serum or oral fluid specimens.     

Evaluation of a new, rapid test for detecting HCV infection, suitable for use with blood or oral fluid

The availability of a highly accurate, rapid, point-of-care test for hepatitis C virus (HCV) may be useful in addressing the problem of under-diagnosis of HCV, by increasing opportunities for testing outside of traditional clinical settings. A new HCV rapid test device (OraQuick? HCV Rapid Antibody Test), approved recently in Europe for use with venous blood, fingerstick blood, serum, plasma, or oral fluid was evaluated in a multi-center study and performance compared to established laboratory-based tests for detection of HCV. The HCV rapid test was evaluated in prospective testing of subjects with signs and/or symptoms of hepatitis, or who were at risk for hepatitis C using all 5 specimen types. Performance was assessed relative to HCV serostatus established by laboratory methods (EIA, RIBA and PCR) approved in Europe for diagnosis of hepatitis C infection. Sensitivity to antibody in early infection was also compared to EIA in 27 seroconversion panels. In addition, the reliability of the oral fluid sample for accurate detection of anti-HCV was assessed by studying the impact of various potentially interfering conditions of oral health, use of oral care products and consumption of food and drink. In this large study of at-risk and symptomatic persons, the overall specificities of the OraQuick? HCV Rapid Antibody Test were equivalent (99.6-99.9%) for all 5 specimen types and the 95% CIs substantially overlapped. Overall sensitivities were virtually identical for venous blood, fingerstick blood, serum and plasma (99.7-99.9%). Observed sensitivity was slightly lower for oral fluid at 98.1% though the upper CI (99.0%) was equal to the lower CI for venous blood and fingerstick blood. Most of the HCV positive subjects which gave nonreactive results in oral fluid had serological and virological results consistent with resolved infection. Sensitivity for anti-HCV in early seroconversion was virtually identical between the HCV rapid test and EIA. Detection of anti-HCV in oral fluid appeared generally robust to conditions of oral health, consumption of food and drink and use of oral care products. The OraQuick? HCV Rapid Antibody Test demonstrated clinical performance that was equivalent to current laboratory-based EIA. This new, HCV rapid test appears suitable as an aid in the diagnosis of HCV infection and may increase testing opportunities due to its simplicity and flexibility to use multiple specimen types, including fingerstick blood and oral fluid.     

Evaluation of a modified commercial assay in detecting antibody to hepatitis C virus in oral fluids and dried blood spots

Oral fluid testing is an effective alternative to serum antibody testing for surveillance of human immunodeficiency virus (HIV) and hepatitis B infections, and is being extended to hepatitis C infections. The objective of this study was to determine and compare the sensitivity and specificity of a modified commercial assay for the detection of antibody to hepatitis C virus (anti-HCV) in oral fluids collected by two different oral fluid collection devices (the Epitope OraSure trade mark and Sarstedt Salivette ) and in dried fingerprick blood spots. In this study, 253 anti-HCV seropositive patients and 394 blood donors (all anti-HCV negative) were recruited between August 2000 and January 2001. Each participant provided oral fluid specimens by OraSure and Salivette, and at least one dried blood spot. Serum specimens were collected from the patients whenever possible. For those injecting drug users who did not provide a serum specimen, HCV status was established on the basis of previous testing. All the nonserum samples were tested for the presence of anti-HCV, using a modified Ortho HCV 3.0 SAVe enzyme-linked immunosorbent assay (ELISA) protocol. The recommended preliminary cutoffs for the modified ELISA were suboptimal. Further, the sensitivity, specificity, and positive and negative predictive values could be improved by varying the cutoff and taking into account the likely prevalence of HCV in the population under investigation. For instance, given a population with a 50% prevalence of anti-HCV, the optimal sensitivities of the modified assay on OraSure, Salivette, and dried blood spots were 92%, 83%, and virtually 100%, respectively, in contrast to 83%, 59%, and 99% using the preliminary cutoffs. The respective optimal specificities were 99%, 93%, and 100%. In conclusion, oral fluids collected by the OraSure device provide an extremely useful method to conduct public health surveillance of not only HIV, but also hepatitis C, among injecting drug users. In addition, dried blood spot specimens may be useful for surveillance and could be employed as a first line diagnostic specimen.     

HCV antibodies in saliva and urine

Infection with hepatitis C virus (HCV) is usually established by detection of serum antibodies (anti-HCV). This study was conducted in order to evaluate whether saliva and urine may substitute serum for anti-HCV detection. Serum, saliva, and urine were obtained simultaneously from 141 patients with a variety of liver diseases and from 52 patients with autoimmune diseases (systemic lupus erythematosus n = 27 and rheumatoid arthritis n = 25). The cell free fraction of saliva and urine samples was tested for anti-HCV using a modification of a serum anti-HCV kit. Western blot analysis was used as a confirmation method. Of the patients with liver diseases, 73 were anti-HCV-seropositive. Salivary and urinary anti-HCV could be detected in 66 (90%) and 36 (49%) of the anti-HCV-serpositive patients, respectively. The presence of anti-HCV in saliva or urine was not related to the severity of liver disease. All the anti-HCV-seronegative liver patients were negative for salivary anti-HCV and 22 (32%) had urinary anti-HCV. The patients with autoimmune diseases were all anti-HCV-seronegative. None had detectable salivary anti-HCV while 33 (63%) were positive for urinary anti-HCV. Western Blot analysis confirmed the presence of anti-HCV in all serum and saliva samples tested but only in 2/12 urine samples. The results suggest that saliva, but not urine, may serve as a substitute for serum for the determination of anti-HCV positivity. J. Med. Virol. 55:24–27, 1998. © 1998 Wiley-Liss, Inc.     

Modified enzyme immunoassay to detect hepatitis C virus antibodies in oral fluid

Samples of oral fluid collected from 18 patients seropositive for hepatitis C virus (HCV) and 49 seronegative patients were tested for the presence of HCV antibodies with two modified serum-screening kits. The following sensitivities and specificities were obtained: HCV 3.0 assay, 72% and 98%, respectively, and Monolisa anti-HCV assay, 100% and 100%, respectively. The modified Monolisa assay demonstrated a striking concordance between serum and saliva samples. The use of oral fluids offers a convenient and noninvasive method applicable to HCV epidemiological studies and screening of high-risk groups.     

Simultaneous detection of hepatitis C virus (HCV) core antigen and anti-HCV antibodies improves the early detection of HCV infection

To evaluate whether a new enzyme immunoassay developed for the simultaneous detection of hepatitis C virus (HCV) core antigen (Ag) and anti-HCV antibodies (anti-HCV Ab) (Monolisa HCV Ag/Ab ULTRA; Bio-Rad) could improve the early detection of HCV infection, we compared its sensitivity to that of anti-HCV, HCV core Ag, and HCV RNA assays. The populations studied included 12 blood donor samples positive for HCV RNA and HCV core Ag but negative for anti-HCV antibodies and 23 hemodialysis patients who developed anti-HCV Ab (seroconversion) during the follow-up. From these 23 individuals, 83 samples sequentially collected prior to seroconversion and 108 samples collected after seroconversion were tested. Six of 12 blood donations were positive by the HCV Ag/Ab assay. In the hemodialysis cohort, the 24 HCV RNA-negative samples were negative by the HCV Ag/Ab assay and 23 of the 59 HCV RNA-positive samples (39%) were positive. The HCV Ag/Ab assay detected HCV infection on average 21.6 days before the most sensitive antibody assay. The HCV Ag/Ab assay did not detect HCV infection as early as the HCV RNA assay (mean delay, 30.3 days) or HCV Ag assay (mean delays, 27.9, and 16.3 days by the HCV core Ag quantification assay and the HCV Ag blood screening assay, respectively). This new assay provides a notable improvement for the early detection of HCV infection during the so-called window period compared with anti-HCV Ab assays and could be a useful alternative to HCV RNA detection or HCV core Ag assays for diagnosis or blood screening when nucleic acid technologies or HCV core Ag detection are not implemented.     

Evaluation of a commercial assay for the detection of mumps specific IgM antibodies in oral fluid and serum specimens.

BACKGROUND: An IgM antibody capture radioimmunoassay (MACRIA) has been used in the UK Reference Laboratory for the detection of mumps specific IgM antibodies in oral fluid and serum samples. The method has proved both sensitive and specific and has been used for the surveillance of mumps since 1994. The use of radioactive labels has restricted the use of MACRIA to specialised laboratories and alternative, non-isotopic, sensitive assays capable of detecting the low levels of specific antibodies in oral fluid have not been available. Recently, a novel mumps specific IgM capture enzyme immunoassay (MACEIA) utilising recombinant mumps nucleoprotein (rMuVN) and monoclonal antibodies to the nucleoprotein, produced by Microimmune Limited, has been developed for use with both serum and oral fluid samples. OBJECTIVES: In this study, we have evaluated the performance of the Microimmune MACEIA for both serum and oral fluid against specimens tested by MACRIA. STUDY DESIGN: The panel consisted of matched serum and oral fluid specimens from 137 cases of suspected mumps received in the Virus Reference Department for routine investigation from March 2003 to October 2004. RESULTS: The sensitivity, specificity, positive and negative predictive value of the Microimmune MACEIA on serum samples compared to MACRIA were 98.8%, 100.0%, 100.0% and 98.5%, respectively. The sensitivity, specificity, positive and negative predictive value of the Microimmune MACEIA on oral fluid samples compared to Microimmune MACEIA and MACRIA consensus results on the paired serum samples were 90.3%, 97.6%, 98.3% and 87.1%, respectively. CONCLUSIONS: The Microimmune MACEIA was found to be a rapid, sensitive and specific alternative to MACRIA for the detection of mumps specific IgM in sera and oral fluids.     

Recognition of multiple classes of hepatitis C antibodies increases detection sensitivity in oral fluid.

Paired serum-oral fluid samples from 127 hepatitis C virus (HCV)-positive and 31 HCV-negative patients were tested for the presence of anti-HCV using the Ortho HCV 3.0 ELISA. Using the immunoglobulin G (IgG)-specific detection antibody provided with the HCV 3.0 ELISA we attained 100% sensitivity and specificity with serum samples; however, sensitivity in oral fluid samples was only 81%. By modifying the HCV 3.0 ELISA to utilize a secondary antibody cocktail that recognizes not only IgG but IgA and IgM as well, we attained 100% specificity and sensitivity with oral fluid samples.     

Twenty-four mini-pool HCV RNA screening outside a blood transfusion setting: results of a 2-year prospective study

The usefulness of 24 mini-pool hepatitis C virus (HCV) RNA screening was evaluated in a 2-year prospective study carried out on a total of 6432 consecutive anti-HCV negative specimens in a routine diagnostic laboratory setting. A total of 268 mini-pools were tested using an automated commercial PCR assay for qualitative detection of HCV RNA, with a lower limit of detection of 50 IU/ml. Eighteen (0.28%) anti-HCV negative/HCV RNA positive serum samples obtained from 12 patients (all intravenous drug users), were detected. Ten patients responded to an invitation for follow-up testing. Five, three and one patient seroconverted in the first, second and third follow-up sample, respectively. One patient had not seroconverted by the end of the study period. The interval between the first HCV RNA positive sample and the first anti-HCV positive samples was 24–192 days. The costs of detecting a single anti-HCV negative/HCV RNA positive sample and a single anti-HCV negative/HCV RNA positive patient using the 24 mini-pool HCV RNA screening strategy were estimated to be around €643 and 965, respectively. It was shown that screening for HCV infection using the 24 mini-pool HCV RNA screening strategy can also be both useful and cost effective outside a blood transfusion setting.     

Detection of Antibodies to Hepatitis C Virus in Dried Blood Spot Samples from Mothers and Their Offspring in Lahore, Pakistan

Dried blood spot samples from mothers and their offspring attending the obstetric and pediatric departments of two hospitals in Lahore, Pakistan, were tested for antibodies to hepatitis C virus (HCV). The seroprevalence of HCV in the women was 6.7% (95% confidence interval [CI], 4.3 to 9.1), and that in the children was 1.3% (95% CI, 0.34 to 2.26). Four anti-HCV immunoglobulin G (IgG)-positive children had mothers that were anti-HCV IgG negative, which suggested that their infection was community acquired.     

游离丙型肝炎病毒核心抗原检测的临床价值探讨

目的:探讨游离丙型肝炎病毒(HCV)核心抗原检测在HCV感染诊断中的价值。方法:采用荧光定量PCR法检测HCV-RNA、ELISA法同步检测抗-HCV和游离HCV核心抗原。结果:191例HCV感染者HCV-RNA的检出率为71·2%(136/191);抗-HCV的检出率为97·4%(186/191);游离HCV核心抗原的检出率为33·0%(63/191)。其中有2例经抗病毒治疗的患者HCV-RNA和抗-HCV检测均阴性,但游离HCV核心抗原检测阳性;另有1例患者抗-HCV阴性,而游离HCV核心抗原阳性,经HCV-RNA证实为HCV感染。27例非HCV感染者HCV-RNA、抗-HCV和游离HCV核心抗原检测结果均为阴性。结论:HCV核心抗原检测作为抗-HCV检验的补充试验对HCV感染的诊断具有重要价值。     

Usefulness of the hepatitis C virus core antigen assay for screening of a population undergoing routine medical checkup

We studied the usefulness of the recently designed Trak-C assay for the detection and quantification of the hepatitis C virus (HCV) core antigen (Ag) for the screening of HCV infection in 4,201 subjects selected from 74,150 consecutive volunteers undergoing routine medical checkups. Subjects were selected for screening because they had risk factors (group II, n = 321) and/or elevated alanine transaminase activity (group I, n = 3847). Initially, the anti-HCV antibody assay and the Trak-C assay were performed on each patient. Subsequently, the Trak-C assay was performed only when the anti-HCV enzyme immune assay (EIA) was positive. Positive samples were further evaluated for anti-HCV antibodies by a third-generation strip immunoblot assay and for HCV RNA. Four samples (1.2%) from group II and 113 (2.9%) from group I were anti-HCV EIA positive. We also tested 33 subjects who previously tested positive for anti-HCV in our medical center. Among the 150 anti-HCV EIA-positive samples, the HCV core Ag result was in accord with the HCV RNA result in 146 cases (97.3%). When the EIA result was positive, the HCV core Ag concentration and the HCV RNA load were correlated (r(2) = 0.78; P < 0.001). Four samples with low viral loads were Trak-C negative but HCV RNA positive. Among the 2,395 anti-HCV EIA-negative serum samples collected during the first part of the study, 17 (0.7%) were found to contain very low levels of HCV core Ag (<8.5 pg/ml, the cutoff value being 1.5 pg/ml). All these samples were HCV RNA negative and considered to be false positives. This was confirmed by HCV core Ag neutralization analysis. The HCV core Ag assay is a useful method in the screening strategy of HCV infection and provides a reliable means of distinguishing between current and cleared HCV infections that is well correlated with HCV RNA testing.