Validation of a single-platform, volumetric, flow cytometry for CD4 T cell count monitoring in therapeutic mobile unit

Evaluation of a collaborative model for successful implementation of a National CD4 enumeration EQA program in Cameroon

Participation in an EQA program is critical to the quality assurance process. Reliable and precise CD4 T-cells enumeration are essential to improve the clinical management of patients by evaluating the disease progression and by monitoring the effectiveness of ART in HIV-patients. The CIRCB, CD4 reference laboratory, in collaboration with the Canadian QASI-program, recruited sites, distributed and analyzed CD4-panels in 61 sites across Cameroon. A trend and performance analysis in the pre-analytical, analytical and post-analytical phases was performed. Continuous training and corrective actions carried out from 2014 to 2018 increased the number of participating sites from 15 to 61 sites, the number of unacceptable results decreased from 50 to 10%. Specific challenges included errors in pre analytic (17.5%), analytic (77.0%) and post-analytic (5.5%) phases. This EQA requires the application of good laboratory practices, fluidic communication between all the stakeholders, continuous training, application of specific on-site corrective measures, and timely equipment maintenance in order to avoid repetitive errors and to increase laboratory performance. It could be extended to other HIV-1 testing like viral load and EID point-of-care. Partnership with QASI serve as a model for implementation of a successful EQA model for resource limited countries wanting to implement EQA for HIV testing and monitoring in alignment with 90–90–90 targets.

[Evaluation of the performances of the "MUSE AUTO CD4/CD4%" flow cytometer vs "GUAVA AUTO CD4/CD4%" flow cytometer for measuring the rate of CD4 lymphocytes in patients infected with HIV in Cameroon]

Introduction

This study aimed to evaluate the performances of the MUSE^® flow cytometer compared with the reference GUAVA^® flow cytometer.

Methods

We conducted an experimental study on HIV-infected patient samples. Venous blood samples, collected in a K3 EDTA tube, were analyzed within 24-48 hours by MUSE^® and GUAVA^® cytometers at the International Center for medical diagnosis (Centre International de Diagnostic médical) in Yaoundé.

Results

In total, 227 samples were analyzed. There was a strong intraclass correlation (p<0.0001) between MUSE^® and GUAVA^® cytometers with a correlation coefficient 0.998 (95% CI: 0,998-0,999) for the absolute values and 0,992 (95% CI: 0,989-0,994) for the percentages. A strong positive linear correlation (p=0.0001) was found between MUSE^® and GUAVA^® cytometers with linear regression slope r2 = 0.98 (95% CI=0,97-0,99) for the absolute values and r2= 0.98 (95% CI= 0.96-1,00) for the percentages. The biases were -4,80 cells/µl (-101.31-91.71) for the absolute values and -0.89% (IC: -6,08-4.3) for the percentages. The percentage of data points outside the limits of agreement was 12/227 (5.29%) and 10/227 (4.41%) respectively for the absolute values and percentages. Cohen's kappa coefficient was 0.92 and the area under the curve was 0,9975 (CI 95%: 0.99-1).

Conclusion

MUSE^®AUTO CD4/CD4% cytometer is a powerful instrument because its results are consistent with those obtained by the reference cytometer. It can enable tracking of patients infected with HIV, in particular in the developing countries.

Performance evaluation of the touchscreen-based Muse™ Auto CD4/CD4% single-platform system for CD4 T cell numeration in absolute number and in percentage using blood samples from children and adult patients living in the Central African Republic

Background

The new microcapillary and fluorescence-based EC IVD-qualified Muse™ Auto CD4/CD4% single-platform assay (EMD Millipore Corporation, Merck Life Sciences, KGaA, Darmstadt, Germany) for CD4 T cell numeration in absolute number and in percentage was evaluated using Central African patients’ samples compared against the reference EC IVD-qualified BD FACSCount (Becton–Dickinson, USA) flow cytometer.

Methods

EDTA-blood samples from 124 adults, 10 adolescents, 13 children and 3 infants were tested in parallel at 2 reference laboratories in Bangui.

Results

The Muse™ technique was highly reproducible, with low intra- and inter-run variabilities less than 15%. CD4 T cell counts of Muse™ and BD FACSCount in absolute number and percentage were highly correlated (r² = 0.99 and 0.98, respectively). The mean absolute bias between Muse™ and BD FACSCount cells in absolute number and percentage were −5.91 cells/µl (95% CI −20.90 to 9.08) with limits of agreement from −77.50 to 202.40 cells/µl, and +1.69 %CD4 (95% CI ±1.29 to +2.09), respectively. The percentages of outliers outside the limits of agreement were nearly similar in absolute number (8%) and percentage (10%). CD4 T cell counting by Muse™ allowed identifying the majority of individuals with CD4 T cell <200, <350 or <750 cells/µl corresponding to the relevant thresholds of therapeutic care, with sensitivities of 95.5–100% and specificities of 83.9–100%.

Conclusions

The Muse™ Auto CD4/CD4% Assay analyzer is a reliable alternative flow cytometer for CD4 T lymphocyte enumeration to be used in routine immunological monitoring according to World Health Organization recommendations in HIV-infected adults as well as children living in resource-constrained settings.

CD4 enumeration technologies: a systematic review of test performance for determining eligibility for antiretroviral therapy

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.

Field evaluation in Chad of community usage of CD4 T lymphocyte counting by alternative single-platform flow cytometry

Background

Field and community evaluation of the routine usage of CD4 T counting platforms is essential in resource-poor countries for efficient and cost-effective monitoring of HIV-infected adults and children attending health care centers.

Methods

We herein addressed the principal issues raised by the implementation of the single-platform, volumetric Auto40 flow cytometer (Apogee Flow Systems Ltd, Hemel Hempstead, UK) in 8 community HIV monitoring laboratories of different levels throughout Chad. This is a country with particularly difficult conditions, both in terms of climate and vast geographical territory, making the decentralization of the therapeutic management of HIV-infected patients challenging.

Results

The routine usage of the Auto40 flow cytometers for a period of 5 years (2008–2013) confirms the reliability and robustness of the analyzer for community-based CD4 T cell enumeration in terms of both absolute numbers and percentages to enable accurate monitoring of HIV-infected adults and children. However, our observations suggest that the Auto40 mini flow cytometer is not suitable for all laboratories as it is oversized and ultimately very expensive.

Conclusion

The Chad experience with the Auto40 flow cytometer suggests that its usage in resource-limited settings should be mainly reserved to reference (level 1) or district (level 2) laboratories, rather than to laboratories of health care centres (level 3).

Single-platform, volumetric, CD45-assisted pan-leucogating flow cytometry for CD4 T lymphocytes monitoring of HIV infection according to the WHO recommendations for resource-constrained settings

Background

Validation of new affordable CD4 T cell measurement technologies is crucial specifically in resource-poor countries for antiretroviral treatment eligibility and immunologic CD4 monitoring of HIV-infected patients.

Methods

The absolute and percentage CD4 T cell counts of 258 HIV-1-infected blood samples (182 adults and 76 children), living in N’Djamena, Chad, were performed by single-platform, volumetric, CD45-assisted pan-leucogating Auto40 flow cytometer (Apogee Flow Systems Ltd, Hemel Hempstead, UK) comparing to the FACSCalibur flow cytometer as a reference method.

Results

Absolute and percentage CD4 T cell counts obtained by Auto40 and FACSCalibur of 258 HIV-1-infected blood samples were highly correlated (r = 0.99 and r = 0.96, respectively). The mean absolute bias and percent bias between Apogee Auto40 and FACSCalibur absolute CD4 T cell counts, were −9.4 cells/μl with limits of agreement from −15 to 93 cells/μl, and +2.0% with limits of agreement from −0.9 to 4.9%, respectively. The mean of absolute bias and percent bias between Apogee Auto40 and FACSCalibur of CD4 percentage results were +0.4% (95% CI: -0.02 – 0.86) with limits of agreement from −2.4 to 0.3%, and +3.0% with limits of agreement from −6.6 to 0.6%, respectively. The Auto40 counting allowed to identify the majority of adults with CD4 T cells below 200 cells/μl (sensitivity: 89%; specificity: 99%) or below 350 cells/μl (sensitivity: 94%; specificity:98%); and of children below 750 cells/μl (sensitivity: 99%; specificity: 96%) or below 25% CD4+ (sensitivity: 94%; specificity: 98%).

Conclusion

The Auto40 analyzer is an alternative flow cytometer for CD4 T lymphocyte enumeration to be used in routine for immunological monitoring according to the current WHO recommendations in HIV-infected adults as well as children living in resource-constrained settings like Chad.

HIV in the tropics: staging in the resource-limited setting

PURPOSE OF REVIEW

In 2010, the WHO updated HIV treatment guidelines for adults and children, expanding the eligibility of HIV-infected individuals for antiretroviral therapy (ART) on the basis of immunological staging. We discuss the barriers to HIV staging in under-resourced settings.

RECENT FINDINGS

In industrialized countries, HIV-infected patients are immunologically staged using CD4 lymphocyte counts measured using flow cytometry, but reliable and timely CD4 testing is still not readily available for all patients in many poorly resourced countries. Often CD4 testing is only available in central hospitals and clinics and depends upon availability of reagents. This leaves clinical staging as the standard of care in many places. Significant discrepancies exist between clinical and immunologic staging. Lack of immunologic staging can lead to delayed or inappropriate initiation of ART, increased attrition before ART, and overall poorer outcomes as patients often initiate ART at lower CD4 cell count baselines. This has led to intensive efforts to develop cost-effective laboratory testing, particularly for accurate low-cost CD4 testing.

SUMMARY

Simplified, low-cost alternatives for immunologic staging are vital to continued scale up of ART programs globally. Point-of-care CD4 testing in particular has shown promise in decreasing attrition rates before ART and improving overall mortality in resource-limited settings.