Rapid Immunoassay Alone Is Insufficient for the Detection of Hepatitis C Virus Infection Among High-risk Population

R. Firdaus; K. Saha; P. C. Sadhukhan

Disclosures

J Viral Hepat. 2013;20(4):290-293. 

In This Article

Results and Discussion

The study involved 612 patients who were screened for HCV infection using rapid immunoassay kits. Seventy-nine per cent of the patients belonged to 40–60 age group, of which 74% of the patients were men and 26% women.

All serum samples selected in this study were evaluated using two different rapid HCV immunodetection kits, namely TRI-DOT and Signal HCV. Of the total 612 samples, 254 (41.50%) reported as HCV nonreactive were screened for this study. Furthermore, of the 254 samples, 40 (15.74%) were seroreactive by both the ELISA methods. All the seropositive samples were screened for HCV RNA detection; among them, 28 (70%) were HCV RNA positive.

Fifteen-ELISA-nonreactive samples from HRG with a history of chronic liver disease and high AST and ALT values were processed for HCV RNA detection. Five samples were HCV RNA positive, of which three were IVDUs and other two were HIV-co-infected patients with a history of surgery and blood transfusion (Table 1). All these HCV RNA-positive samples were further processed for viral quantitation and genotyping. It was found that the viral load ranged from 1.2 × 102 to 4.4 × 106 IU/mL and four were genotype 3, whereas one was genotype 1 (Table 1). The median ALT value was calculated at 45 IU/mL (min. 15.55, max. 111.32 IU/mL) and AST at 109.63 IU/mL, respectively (min. 60.23, max. 293.36 IU/mL) (Table 1).

From our results, we could surmise that HCV rapid immunoassay gave false-negative results in patients belonging to high-risk group especially in IVDUs, haemodialysis, thalassaemic, and HIV-co-infected patients. 11.02% of samples marked as rapid immunoassay nonreactive were in fact HCV RNA positive as determined by NAT (HCV RNA) assays. Results obtained were compared by additionally testing the samples using ELISAs and NAT. Two different ELISA kits were used to compare the specificity of the results. Forty (15.74%) samples were seropositive by both the HCV ELISA kits. In addition, the findings showed that of 15 ELISA-seronegative samples, five were HCV RNA positive, that is, the patients were active carriers of the HCV infection. All the seronegative samples that were HCV RNA positive belonged to patients in high-risk group. One of the striking observations was that even though these patients were asymptomatic and declared as HCV nonreactive by rapid immunoassay, they had high levels of ALT and AST values that indicated a dysfunction in their liver.

Our genotyping data showed that of the HCV RNA-positive patients, 80% were infected with genotype 3. The viral load in patients with genotype 3 was significantly lower than in those infected with genotype 1. Diagnosis of HCV in these cases is difficult, as these patients cannot produce sufficient anti-HCV antibodies because of immunosuppression.[8] Additionally, false-negative results could be attributed to genetic heterogeneity, which could affect the serological response. The most prevalent HCV strain in India is genotype 3,[9] which is a slow-growing variant, and therefore, the probability of false negatives for this genotype may increase in rapid immunoassay tests. Although HCV rapid immunoassays are routinely used in practically all laboratories, our results showed for the first time that many of the samples declared as HCV rapid immunoassay nonreactive in initial screening were in fact HCV RNA positive, that is, the patients were active carriers of the infection. This shows that rapid tests might give false-negative results particularly for patients belonging to HRG. Missing positivity in immunoassays occurs mainly in immunocompromised patients who fail to clear away the antigens or in patients with autoimmune disorders, hyperglobulinemia or in low-risk blood donors who donate blood frequently. In these cases, confirmatory HCV tests by nucleic acid amplification test (NAT) assays remain the method of choice. The presence of HCV RNA in a patient's serum confirms the active state of infection.

To conclude, the present study highlights that HCV rapid immunoassay tests should not relied upon as the sole criterion for screening patients in high-risk group. In these cases, confirmatory methods should be deployed for HCV detection, so that the rate of false-negative results can be scaled down, and the patients can be effectively screened and put on medication as soon as possible. Although this study is in a preliminary stage, it aims to provide useful inputs to scientific community and the policy makers to improve the existing infrastructure in screening patients for HCV.

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