Jean Maritz1, Wolfgang Preiser, Gert U van Zyl. 1. Division of Medical Virology, Department of Pathology, Faculty of Health Sciences, Stellenbosch University and National Health Laboratory Service Tygerberg, P.O. Box 19063, Tygerberg 7505, South Africa. maritzj@sun.ac.za
Abstract
BACKGROUND: As antibody testing cannot confirm HIV-1 infection in children less than 18 months of age, diagnosis in these children depends on nucleic acid testing. The COBAS(®) AmpliPrep/COBAS(®) TaqMan(®) (CAP/CTM, Roche(®) Molecular Systems, Inc., Branchburg, NJ) HIV-1 Qualitative test is a total nucleic acid real-time PCR assay utilising whole EDTA blood or dried blood spots (DBS), which recently replaced the Roche(®) AMPLICOR(®) DNA test v1.5 (Amplicor) as the diagnostic HIV PCR assay in many South African laboratories. For the Amplicor assay, stringent diagnostic criteria were previously formulated for the local population, and a comparison reported the CAP/CTM's sensitivity at 99.7% and specificity at 100% for both sample types compared to these Amplicor criteria. OBJECTIVES: To validate the assay prior to introduction in our laboratory and to define stringent diagnostic cut-off criteria. STUDY DESIGN: Whole EDTA blood samples from patients younger than 18 months sent for routine HIV-1 diagnosis were tested by Amplicor, and positive results were confirmed from DBS. CAP/CTM assays were subsequently performed from DBS. RESULTS: The CAP/CTM had a sensitivity of 98.8% and a specificity of 97.1%, but a positive predictive value (PPV) of only 78.7% compared to the Amplicor assay. Samples positive by CAP/CTM but negative by Amplicor displayed poor amplification curves compared to concordant positive samples. Upon re-testing those with sufficient material available by CAP/CTM, all showed negative results. CONCLUSIONS: The decreased PPV may either be due to false positive CAP/CTM results, or increased sensitivity compared to the Amplicor assay. Criteria were formulated for defining presumed false-positive results.
BACKGROUND: As antibody testing cannot confirm HIV-1 infection in children less than 18 months of age, diagnosis in these children depends on nucleic acid testing. The COBAS(®) AmpliPrep/COBAS(®) TaqMan(®) (CAP/CTM, Roche(®) Molecular Systems, Inc., Branchburg, NJ) HIV-1 Qualitative test is a total nucleic acid real-time PCR assay utilising whole EDTA blood or dried blood spots (DBS), which recently replaced the Roche(®) AMPLICOR(®) DNA test v1.5 (Amplicor) as the diagnostic HIV PCR assay in many South African laboratories. For the Amplicor assay, stringent diagnostic criteria were previously formulated for the local population, and a comparison reported the CAP/CTM's sensitivity at 99.7% and specificity at 100% for both sample types compared to these Amplicor criteria. OBJECTIVES: To validate the assay prior to introduction in our laboratory and to define stringent diagnostic cut-off criteria. STUDY DESIGN: Whole EDTA blood samples from patients younger than 18 months sent for routine HIV-1 diagnosis were tested by Amplicor, and positive results were confirmed from DBS. CAP/CTM assays were subsequently performed from DBS. RESULTS: The CAP/CTM had a sensitivity of 98.8% and a specificity of 97.1%, but a positive predictive value (PPV) of only 78.7% compared to the Amplicor assay. Samples positive by CAP/CTM but negative by Amplicor displayed poor amplification curves compared to concordant positive samples. Upon re-testing those with sufficient material available by CAP/CTM, all showed negative results. CONCLUSIONS: The decreased PPV may either be due to false positive CAP/CTM results, or increased sensitivity compared to the Amplicor assay. Criteria were formulated for defining presumed false-positive results.
Authors: Renate Strehlau; Maria Paximadis; Faeezah Patel; Megan Burke; Karl-Gunter Technau; Stephanie Shiau; Elaine J Abrams; Gayle G Sherman; Gillian Hunt; Johanna Ledwaba; Ahmad H Mazanderani; Caroline T Tiemessen; Louise Kuhn Journal: AIDS Date: 2019-09-01 Impact factor: 4.177
Authors: Ahmad Haeri Mazanderani; Karl-Günter Technau; Nei-Yuan Hsiao; Jean Maritz; Sergio Carmona; Gayle G Sherman Journal: South Afr J HIV Med Date: 2016-05-13 Impact factor: 2.744