Analytical and Clinical Performance Evaluation of the Elecsys HIV Combi PT Assay on the Cobas e 602 Analyzer for the Diagnosis of Human Immunodeficiency Virus

Denise L. Uettwiller-Geiger, PhD; Marvin Lessig, DO; Jie An, PhD; Tara Barsch; Susan Smith; Sharan Walker; Alexander Riedel, PhD; Yi Hao, MSc; Amin A. Mohammad, PhD


Am J Clin Pathol. 2019;151(4):377-385. 

In This Article

Abstract and Introduction


Objectives: We evaluated the performance of the Elecsys HIV combi PT assay on the cobas e 602 analyzer for diagnosing human immunodeficiency virus (HIV; part of the US Food and Drug Administration [FDA] submission).

Methods: The HIV combi PT and reference (ARCHITECT HIV Ag/Ab Combo) assays were assessed at four independent clinical laboratories/one reference laboratory (United States; July 2014 to November 2015). Clinical performance was evaluated using four reagent lots. Analytical performance was evaluated per Clinical and Laboratory Standards Institute EP05-A3 guidelines. Serum/plasma samples from 18 clinical sites/vendors (United States and outside the United States) were tested.

Results: Sensitivity (95% confidence interval [CI]) in HIV-1 antibody-positive individuals (United States and outside the United States; n = 1,460) was 100.00% (99.75%-100.00%). Specificity was 99.94% (95% CI, 99.85%-99.98%) in low-risk individuals (United States; n = 6,843), 98.19% (95% CI, 96.93%-99.04%) in high-risk individuals (United States and outside the United States; n = 758), and 97.43% (95% CI, 95.32%-98.76%) in pregnant women (United States and outside the United States; n = 440). Analytical performance was acceptable.

Conclusions: We demonstrate the robustness of the FDA-approved Elecsys HIV combi PT assay on the cobas e 602 analyzer for HIV testing in the United States.


Over 36 million people have human immunodeficiency virus (HIV) worldwide, with approximately 2 million new cases annually.[1] In the United States, approximately 1.2 million people have HIV, of whom 13% remain undiagnosed.[2] The two main strains of HIV are HIV-1, categorized into groups M (the most common group, with nine subtypes), O, N, and P, and HIV-2.[1] In areas where diverse subtypes are prevalent, HIV diagnostic assays must be sensitive to the full range of groups and subtypes. Early viral identification facilitates timely initiation of antiretroviral therapy, which can increase life expectancy.[3] Therefore, reliable HIV screening is important to reduce the human and financial burden associated with HIV transmission.[4]

HIV diagnosis usually requires detection of the HIV-1 p24 antigen or antibodies to HIV-1 and HIV-2, and confirmatory tests are performed according to Centers for Disease Control and Prevention (CDC) recommendations.[5,6] The Elecsys HIV combi PT assay (fourth generation; Roche Diagnostics) is a qualitative, serologic sandwich assay intended for simultaneous in vitro determination of HIV-1 p24 antigen and antibodies to HIV-1 (including group O) and HIV-2 in human serum or plasma. Unlike previous Elecsys HIV combi assays, the Elecsys HIV combi PT assay includes a pretreatment step, which enhances sensitivity and specificity for the HIV-1 p24 antigen and improves early detection of HIV seroconversion. The Elecsys HIV combi PT assay has been shown to reliably detect all known HIV subtypes using the Elecsys 2010 (Roche Diagnostics), cobas e 411 (Roche Diagnostics), or MODULAR E170 (Roche Diagnostics) analyzers.[7] The assay has also been validated for screening and detection of HIV in Asia and is Conformité Européenne approved for use in Europe.[7,8]

This study aimed to validate the performance of the Elecsys HIV combi PT assay on the cobas e 602 system (Roche Diagnostics) under routine laboratory conditions in the United States (part of the US Food and Drug Administration [FDA] submission).

The walkaway, freestanding cobas e 602 immunoassay analyzer (throughput 170 tests per hour) is compatible with 61 assays and can simultaneously test 25 different biomarkers in either random access or batch mode. The analyzer is equipped with onboard reagent refrigeration and dilution, as well as clot/serum indices (icterus, hemolysis, and lipemia) detection, and capable of over 16 hours of continuous testing per day. Autocalibration, onboard quality control monitoring, and data storage facilitate data tracking and maintaining study logs.