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 90.6. The ROC curve for S/CO ratio showed excellent sensitivity and specificity result when compared to RIBA test (AUC 0.98, Standard error 0.0087, 95% Confidence Interval 0.95 to 0.99, P value <0.0001).

Table 2: ROC curve: Area under the curve ( AUC)

DeLong et al., 1988 Binomial exact Youden index

Area under the ROC curve (AUC)

0.982504

Standard Errora 0.00870

95% Confidence intervalb 0.951230 to 0.996118

z statistic 55.482

Significance level P (Area=0.5)

<0.0001

Sample size 183

Youden index J 0.9347

Associated criterion >8.79

HCV Signal-to-Cutoff Ratio in Predicting Hepatitis C ViremiaH.AbdelazizDr. Hisham AbdElaziz, MD, Lecturer of Hematology, National Cancer Institute, University of Cairo, Egypt.

Table 1. Correlation (r): Between CLIA and RIBA tests for diagnosis of HCV infection

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.

Establishing optimal S/CO ratio can serve as an alternative to a supplemental test to avoid unnecessary further HCV tests.

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.

Table 5: S/CO ratios for commercially available assays: http://www.cdc.gov/hepatitis/HCV/LabTesting.htm

Table 3: Cutoff Criterion values and coordinates of the ROC curve

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.

hishamaziz2002@yahoo.com

AIM

METHODS

RESULTS (Cont.)

CONCLUSION

INTRODUCTION

CONTACT INFORMATION

Sample size 183

Correlation coefficient r 0.8322

Significance level P<0.0001

95% Confidence interval for r 0.7815 to 0.8720

Cutoff Sensitivity 95% CI Specificity 95% CI +LR -LR +PV -PV

>5.02 95.97 90.8 - 98.7 91.53 81.3 - 97.2 11.32 0.044 96.0 91.5

>5.19 95.16 89.8 - 98.2 91.53 81.3 - 97.2 11.23 0.053 95.9 90.0

>8.79 95.16 89.8 - 98.2 98.31 90.9 - 100.0 56.15 0.049 99.2 90.6

>18.6 84.68 77.1 - 90.5 98.31 90.9 - 100.0 49.96 0.16 99.1 75.3

Graph 1: Roc Curve: showing perfect specificity and sensitivity between CLIA and RIBA tests for diagnosis of HCV infection

test

0 20 40 60 80 1000

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40

60

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100

100-Specificity

Se

nsitiv

ity

test

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diagnosis0 1

>8.79Sens: 95.2Spec: 98.3

Graph 2: S/Co ratio cutoff value: Shows the best sensitivity and specificity of CLIA S/CO ratio for diagnosis of HCV infection.

Screening TestKit Name

Manufacturer Assay FormatSignal-to-cut–off ratio predictive of a true

positive ≥ 95% of the time

Ortho HCV Version 3.0 ELISA Test System

OrthoEIA

(Enzyme Immunoassay)≥ 3.8

Abbott HCV EIA 2.0 AbbottEIA

(Enzyme Immunoassay)≥ 3.8

VITROS Anti-HCV OrthoCIA

(Chemiluminescennt Immunoassay)≥ 8.0

AxSYM Anti-HCV AbbottMEIA

(Microparticle Immunoassay)≥ 10.0

Architect Anti-HCV AbbottCMIA

(Chemiluminescent Microparticle Immunoassay)

≥ 5.0

Advia Centaur HCV BayerCIA

(Chemiluminescennt Immunoassay)≥ 11.0

RESULTS