Browsing by Author "Barnett, David"

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    CD4 enumeration technologies: a systematic review of test performance for determining eligibility for antiretroviral therapy.
    (PLoS One, 2015) Peeling, Rosanna W; Sollis, Kimberly A; Glover, Sarah; Crowe, Suzanne M; Landay, Alan L; Cheng, Ben; Barnett, David; Denny, Thomas N; Spira, Thomas J; Stevens, Wendy S; Crowley, Siobhan; Essajee, Shaffiq; Vitoria, Marco; Ford, Nathan
    BACKGROUND: Measurement of CD4+ T-lymphocytes (CD4) is a crucial parameter in the management of HIV patients, particularly in determining eligibility to initiate antiretroviral treatment (ART). A number of technologies exist for CD4 enumeration, with considerable variation in cost, complexity, and operational requirements. We conducted a systematic review of the performance of technologies for CD4 enumeration. METHODS AND FINDINGS: Studies were identified by searching electronic databases MEDLINE and EMBASE using a pre-defined search strategy. Data on test accuracy and precision included bias and limits of agreement with a reference standard, and misclassification probabilities around CD4 thresholds of 200 and 350 cells/μl over a clinically relevant range. The secondary outcome measure was test imprecision, expressed as % coefficient of variation. Thirty-two studies evaluating 15 CD4 technologies were included, of which less than half presented data on bias and misclassification compared to the same reference technology. At CD4 counts <350 cells/μl, bias ranged from -35.2 to +13.1 cells/μl while at counts >350 cells/μl, bias ranged from -70.7 to +47 cells/μl, compared to the BD FACSCount as a reference technology. Misclassification around the threshold of 350 cells/μl ranged from 1-29% for upward classification, resulting in under-treatment, and 7-68% for downward classification resulting in overtreatment. Less than half of these studies reported within laboratory precision or reproducibility of the CD4 values obtained. CONCLUSIONS: A wide range of bias and percent misclassification around treatment thresholds were reported on the CD4 enumeration technologies included in this review, with few studies reporting assay precision. The lack of standardised methodology on test evaluation, including the use of different reference standards, is a barrier to assessing relative assay performance and could hinder the introduction of new point-of-care assays in countries where they are most needed.
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    Laboratory accuracy improvement in the uk neqas leucocyte immunophenotyping immune monitoring program: An eleven-year review via longitudinal mixed effects modeling.
    (Cytometry B Clin Cytom, 2017-05-08) Bainbridge, John; Rountree, Wes; Louzao, Raul; Wong, John; Whitby, Liam; Denny, Thomas N; Barnett, David
    BACKGROUND: The United Kingdom National External Quality Assessment Service (UK NEQAS) for Leucocyte Immunophenotyping Immune Monitoring Programme, provides external quality assessment (EQA) to non-U.S. laboratories affiliated with the NIH NIAID Division of AIDS (DAIDS) clinical trials networks. Selected laboratories are required to have oversight, performance monitoring, and remediation undertaken by Immunology Quality Assessment (IQA) staff under the DAIDS contract. We examined whether laboratory accuracy improves with longer EQA participation and whether IQA remediation is effective. METHODS: Laboratory accuracy, defined by the measurement residuals from trial sample medians, was measured on four outcomes: both CD4+ absolute counts (cells/μL) and percentages; and CD8+ absolute counts (cells/μL) and percentages. Three laboratory categories were defined: IQA monitored (n = 116), United Kingdom/non-DAIDS (n = 137), and non-DAIDS/non-UK (n = 1034). For absolute count outcomes, the groups were subdivided into single platform and dual platform users. RESULTS: Increasing EQA duration was found to be associated with increasing accuracy for all groups in all four lymphocyte subsets (P < 0.0001). In the percentage outcomes, the typical IQA group laboratory improved faster than laboratories from the other two groups (P < 0.005). No difference in the overall rate of improvement was found between groups for absolute count outcomes. However, in the DPT subgroup the IQA group ultimately showed greater homogeneity. CONCLUSIONS: EQA participation coupled with effective laboratory monitoring and remedial action is strongly associated with improved laboratory accuracy, both incrementally and in the proportion of laboratories meeting suggested standards. Improvement in accuracy provides more reliable laboratory information facilitating more appropriate patient treatment decisions. © 2017 International Clinical Cytometry Society.
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    Systematic review of the performance of HIV viral load technologies on plasma samples.
    (PLoS One, 2014) Sollis, Kimberly A; Smit, Pieter W; Fiscus, Susan; Ford, Nathan; Vitoria, Marco; Essajee, Shaffiq; Barnett, David; Cheng, Ben; Crowe, Suzanne M; Denny, Thomas; Landay, Alan; Stevens, Wendy; Habiyambere, Vincent; Perrins, Jos; Peeling, Rosanna W
    BACKGROUND: Viral load (VL) monitoring is the standard of care in developing country settings for detecting HIV treatment failure. Since 2010 the World Health Organization has recommended a phase-in approach to VL monitoring in resource-limited settings. We conducted a systematic review of the accuracy and precision of HIV VL technologies for treatment monitoring. METHODS AND FINDINGS: A search of Medline and Embase was conducted for studies evaluating the accuracy or reproducibility of commercially available HIV VL assays. 37 studies were included for review including evaluations of the Amplicor Monitor HIV-1 v1.5 (n = 25), Cobas TaqMan v2.0 (n = 11), Abbott RealTime HIV-1 (n = 23), Versant HIV-1 RNA bDNA 3.0 (n = 15), Versant HIV-1 RNA kPCR 1.0 (n = 2), ExaVir Load v3 (n = 2), and NucliSens EasyQ v2.0 (n = 1). All currently available HIV VL assays are of sufficient sensitivity to detect plasma virus levels at a lower detection limit of 1,000 copies/mL. Bias data comparing the Abbott RealTime HIV-1, TaqMan v2.0 to the Amplicor Monitor v1.5 showed a tendency of the Abbott RealTime HIV-1 to under-estimate results while the TaqMan v2.0 overestimated VL counts. Compared to the Amplicor Monitor v1.5, 2-26% and 9-70% of results from the Versant bDNA 3.0 and Abbott RealTime HIV-1 differed by greater than 0.5log10. The average intra and inter-assay variation of the Abbott RealTime HIV-1 were 2.95% (range 2.0-5.1%) and 5.44% (range 1.17-30.00%) across the range of VL counts (2log10-7log10). CONCLUSIONS: This review found that all currently available HIV VL assays are of sufficient sensitivity to detect plasma VL of 1,000 copies/mL as a threshold to initiate investigations of treatment adherence or possible treatment failure. Sources of variability between VL assays include differences in technology platform, plasma input volume, and ability to detect HIV-1 subtypes. Monitoring of individual patients should be performed on the same technology platform to ensure appropriate interpretation of changes in VL. Prospero registration # CD42013003603.
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    Systematic review of the use of dried blood spots for monitoring HIV viral load and for early infant diagnosis.
    (PLoS One, 2014) Smit, Pieter W; Sollis, Kimberly A; Fiscus, Susan; Ford, Nathan; Vitoria, Marco; Essajee, Shaffiq; Barnett, David; Cheng, Ben; Crowe, Suzanne M; Denny, Thomas; Landay, Alan; Stevens, Wendy; Habiyambere, Vincent; Perriens, Joseph H; Peeling, Rosanna W
    BACKGROUND: Dried blood spots (DBS) have been used as alternative specimens to plasma to increase access to HIV viral load (VL) monitoring and early infant diagnosis (EID) in remote settings. We systematically reviewed evidence on the performance of DBS compared to plasma for VL monitoring and EID. METHODS AND FINDINGS: Thirteen peer reviewed HIV VL publications and five HIV EID papers were included. Depending on the technology and the viral load distribution in the study population, the percentage of DBS samples that are within 0.5 log of VL in plasma ranged from 52-100%. Because the input sample volume is much smaller in a blood spot, there is a risk of false negatives with DBS. Sensitivity of DBS VL was found to be 78-100% compared to plasma at VL below 1000 copies/ml, but this increased to 100% at a threshold of 5000 copies/ml. Unlike a plasma VL test which measures only cell free HIV RNA, a DBS VL also measures proviral DNA as well as cell-associated RNA, potentially leading to false positive results when using DBS. The systematic review showed that specificity was close to 100% at DBS VL above 5000 copies/ml, and this threshold would be the most reliable for predicting true virologic failure using DBS. For early infant diagnosis, DBS has a sensitivity of 100% compared to fresh whole blood or plasma in all studies. CONCLUSIONS: Although limited data are available for EID, DBS offer a highly sensitive and specific sampling strategy to make viral load monitoring and early infant diagnosis more accessible in remote settings. A standardized approach for sampling, storing, and processing DBS samples would be essential to allow successful implementation. TRIAL REGISTRATION: PROSPERO Registration #: CRD42013003621.
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    VERITAS?: A time for VERIQAS™ and a new approach to training, education, and the quality assessment of CD4+ T lymphocyte counting (I).
    (Cytometry. Part B, Clinical cytometry, 2012-03) Barnett, David; Whitby, Liam; Wong, John; Louzao, Raul; Reilly, John T; Denny, Thomas N

    Background

    The aim of clinical laboratories is to produce accurate and reproducible results to enable effective and reliable clinical practice and patient management. The standard approach is to use both internal quality control (IQC) and external quality assessment (EQA). IQC serves, in many instances, as a "go, no go" tool to provide real time assurance that instruments and reagent or test systems are performing within defined specifications. EQA however, takes a snapshot at a specific point in time of the full testing process, results are compared to other laboratories performing similar testing but inevitably has some built in delay from sample issue to performance data review. In addition, if IQC or EQA identify areas of concern it can be difficult to determine the exact nature of the problem. In an attempt to address this problem, we have developed an instant QA panel that we have termed VERIQAS™, specifically for CD4(+) T lymphocyte counting, and have undertaken a "proof of principle" pilot study to examine how the use of VERIQAS™ could result in improvement of laboratory performance. In addition, we have examined how this approach could be used as a training and education tool (in a domestic/international setting) and potentially be of value in instrument validation/switch studies (a switch study being defined as a laboratory changing from one method/instrument to a new method/instrument with the VERIQAS™ panel being used as an adjunct to their standard switch study protocol).

    Methods

    The basic panel consists of 20 stabilized samples, with predefined CD4(+) T lymphocyte counts, that span low clinically relevant to normal counts, including some blinded replicates (singlet up to quadruplicate combinations). The CD4(+) T lymphocyte target values for each specimen is defined as the trimmed mean ± 2 trimmed standard deviations, where the trimmed values are derived from the CD4(+) T lymphocyte counts reported by the participating centers (~780 laboratories) that receive each UK NEQAS for Leucocyte Immunophenotyping send out. Results for the VERIQAS™ panel were returned online, via a specially designed website, and the participant was provided with an immediate assessment (pass or fail).

    Results

    To date, the panel has been preliminary trialed by eight laboratories to (i) assess pre-EQA qualification (two laboratories); (ii) address performance issues (two laboratories); or (iii) validate new instruments or techniques (four laboratories). Interestingly, even in this pilot study, the panel has been instrumental in identifying specific technical problems in laboratories with EQA performance issues as well as confirming that implementation of new techniques or instruments have been successful.

    Conclusion

    We report here a new and novel "proof of principle" pilot study to quality assessment, that we have termed VERIQAS™, designed to provide instant feedback on performance. Participating laboratories receive 20 "blinded" samples that are in singlet up to quadruplicate combinations. Once a centre reports its results via a website, immediate feedback is provided to both the participant and the EQA organizers, enabling, if required, the initiation of targeted remedial action. We have also shown that this approach has the potential to be used as a tool for prequalification, troubleshooting, training and instrument verification. Pilot phase field trials with VERIQAS™ have shown that the panel can highlight laboratory performance problems, such as suboptimal instrument set up, pipetting and gating strategies, in a rapid and efficient manner. VERIQAS™ will now be introduced, where appropriate, as a second phase study within UK NEQAS for Leucocyte Immunophenotyping to assist those laboratories that have performance issues and also made available to laboratories for training and education of staff and instrument validation studies.