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

Abstract

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.

Fig 1. PRISMA flow diagram of study selection.

EQA: external quality assurance, FC: flow cytometry.

Fig 2. Methodological quality of included studies.

EQA: external quality assurance, IQC: internal quality control.

Fig 3. A. Bias compared to FASCount as the reference technology. B. Bias compared to FASCalibur as the reference technology.

Fig 4. Misclassification (%), using a CD4 thresholds of 350 cells/μl and 200 cells/μl.

Fig 5. Intra- and inter-assay variation (% CV) for the Apogee Auto 40 and for the MBio SnapCount at thresholds <350 cells/mL and >350 cells/mL.