1. Screening Test Kit Name
HCV Signal-to-Cutoff Ratio in Predicting Hepatitis C Viremia
H.Abdelaziz
Dr. Hisham AbdElaziz, MD, Lecturer of Hematology, National Cancer Institute, University of Cairo, Egypt.
INTRODUCTION
RESULTS (Cont.)
Positive results for HCV antibody screening require confirmation with other more specific supplementary tests such as RIBA or a nucleic acid test. The Center for Disease Control and Prevention (CDC) published guidelines that recommended supplemental tests to be based on anti-HCV assay Signal-to-Cutoff (S/CO) ratio.
Table 2: ROC curve: Area under the curve ( AUC)
DeLong et al., 1988
Binomial exact
Youden index
Sample size
183
Area under the ROC curve (AUC)
Standard Errora
95% Confidence intervalb to
z statistic
55.482
Significance level P (Area=0.5)
<0.0001
Table 1. Correlation (r): Between CLIA and RIBA tests for diagnosis of HCV infection
Sample size
183
Correlation coefficient r
0.8322
Significance level
P<0.0001
95% Confidence interval for r to
Youden index J
0.9347
Associated criterion
>8.79
AIM
Table 3: Cutoff Criterion values and coordinates of the ROC curve
Establishing optimal S/CO ratio can serve as an alternative to a supplemental test to avoid unnecessary further HCV tests.
Cutoff
Sensitivity
95% CI
Specificity
+LR
-LR
+PV
-PV
>5.02
95.97
91.53
11.32
0.044
96.0
91.5
>5.19
95.16
11.23
0.053
95.9
90.0
>8.79
98.31
56.15
0.049
99.2
90.6
>18.6
84.68
49.96
0.16
99.1
75.3
METHODS
Graph 1: Roc Curve: showing perfect specificity and sensitivity between CLIA and RIBA tests for diagnosis of HCV infection
Graph 2: S/Co ratio cutoff value: Shows the best sensitivity and specificity of CLIA S/CO ratio for diagnosis of HCV infection.
One hundred eighty three cases showed positive result by chemiluminescent immunoassay (CLIA), (Vitros EciQ, USA). Those positive cases were reflected for supplemental RIBA test for confirmation of HCV infection. The S/CO ratio then compared it with the result provided from RIBA tests.
RESULTS
The S/CO ratio 8.79 is set as the screening test positive value to determine the need of reflex supplemental test. The sensitivity was 95%, (95%CI 89.8 – 98.2), the specificity was 98% (95%CI 90.9 – 100), positive predictive value was 99.2, and negative predictive value was The ROC curve for S/CO ratio showed excellent sensitivity and specificity result when compared to RIBA test (AUC 0.98, Standard error , 95% Confidence Interval to 0.99, P value <0.0001).
Table 5: S/CO ratios for commercially available assays:
Screening Test Kit Name
Manufacturer
Assay Format
Signal-to-cut–off ratio predictive of a true positive ≥ 95% of the time
Ortho HCV Version 3.0 ELISA Test System
Ortho
EIA (Enzyme Immunoassay)
≥ 3.8
Abbott HCV EIA 2.0
Abbott
VITROS Anti-HCV
CIA (Chemiluminescennt Immunoassay)
≥ 8.0
AxSYM Anti-HCV
MEIA (Microparticle Immunoassay)
≥ 10.0
Architect Anti-HCV
CMIA (Chemiluminescent Microparticle Immunoassay)
≥ 5.0
Advia Centaur HCV
Bayer
≥ 11.0
CONCLUSION
CONTACT INFORMATION
The use of S/CO ratio is better than the signal result of CLIA to reflect HCV infection status of patients. The need for reflex supplemental test (RIBA, RNA-HCV) to confirm the diagnosis of HCV infection should be limited to patients in the grey zone of S/CO ratio with positive results less than 8.7, when using Vitros Immunoassay analyzer. This will effectively reduce the time and cost for the diagnosis of HCV infection. The use of other Immunoassay or ELISA analyzer should set their S/CO ratio to determine the need for supplemental test.