Large-scale affordable PanLeucogated CD4+ testing with proactive internal and external quality assessment: in support of the South African national comprehensive care, treatment and management programme for HIV and AIDS.

BACKGROUND

In order to expand the treatment of human immunodeficiency virus-1 (HIV) infected patients in Africa, millions will require cost-effective CD4 counts. Supporting laboratories therefore, need to move away from crisis management and haphazard practices to organized pathology services. The authors reviewed the performance of the simplified single platform (SP) PanLeucogated (PLG) CD4 methodology, introduced into 52 laboratories across the South African National Health Laboratory Service (SA-NHLS), with a proactive approach to training, internal quality control (IQC), and external quality assessment (EQA).

METHODS

Two-color flow cytometry for SP PLG (CD4/CD45) was combined with the sample-by-sample bead-count-rate (BCR) IQC for bead pipetting. PLG + BCR was validated versus conventional predicate SP and dual-platform (DP) 4-color flow cytometric methods used in the first world-on 1181 samples from 250 HIV+ patients followed longitudinally on anti-retroviral therapy (ART). EQA (accuracy) was performed through the United Kingdom National External Quality Assessment Scheme (UK-NEQAS). Further EQA was performed across the 52 SA-NHLS SP-PLG laboratories participating on the CD4 African Regional External Quality Assessment Scheme (AFREQAS), to assess both accuracy and/precision between NHLS PLG laboratories.

RESULTS

There was virtually no bias noted between SP PLG and SP predicate methods. On DP, bias and variability increased but the errors introduced were minor without affecting CD4-related clinical decisions. The simpler 2-color PLG was less expensive with additional advantages: CD4+ T-cells were discriminated from monocytes without a need for CD3-staining, and the training was faster and easier for the trainees and trainers alike. The accuracy of SP-PLG was satisfactory: all PLG results submitted to the UK NEQAS were within +/-1 Trimmed Standard Deviation (SD) of the UK NEQAS CD4 Pool Trimmed Mean. Further, on the CD4 AFREQAS, the SA-NHLS laboratories using SP-PLG + BCR showed better precision (mean %CV = 7.2%) than the CD4 methods employed in other laboratories in Africa (mean %CV = 10.7%) or on other continents (mean %CV = 12.9%). PLG + BCR accommodated high workloads, exceeding 3,000 tests/laboratory/month, with capacity for further growth around 10% per month across the SA-NHLS.

CONCLUSIONS

The superior performance of PLG + BCR over other methods has been demonstrated. In resource-conscious countries, where large-scale ART is being introduced, flow-cytometry using PLG + BCR can make a significant impact-due to simpler operation, easier training, stricter quality assurance, and better cost-efficiency. These cost-effective flow methods can legitimately replace the more cumbersome predicate technology of the first world for ART monitoring whilst accommodating an ever-expanding national ART program and consequent extremely high workloads reached country-wide.