To the Editors:
The enumeration of absolute count of CD4 cells has become an essential part of staging and monitoring HIV infection and for the initiation of antiretroviral therapy.1
In many developing countries, the high cost of the conventional CD4 tests is an obstacle to their use and a barrier to treatment.2The available CD4 testing systems, based on flow cytometry, require expensive instrumentation and infrastructure3 and are time consuming. Hence, there is a need for rapid, low-cost, point-of-care, CD4 test, especially in primary health care centers.
The objective of this study was to validate the Alere PIMA CD4 test system (Alere, CA), claimed to be a robust, affordable, and easy-to-use point-of-care assay using a battery-operated, portable, benchtop, fixed-volume cytometer that could be a highly effective tool in improving access to CD4 tests.
MATERIALS AND METHODS
A total of 250 whole blood samples were collected in EDTA vacutainer tubes from known HIV reactive cases and were tested by both Alere PIMA (Alere) and BD FACS count systems (Becton Dickinson, NJ) after obtaining an informed consent.
CD4 Testing by PIMA
The PIMA test consists of a disposable PIMA test cartridge, containing dried reagents, and the PIMA Analyzer. The assay was performed as per the instructions of the manufacturer. The test data was recorded, analysed, and interpreted by the software embedded within the Analyser.
CD4 Testing by BD FACs Count
All the 250 samples were tested by BD FACs count as per the instructions of the manufacturer.
The absolute CD4 cell count obtained using the PIMA system correlated with those of the FACS Count for all ranges of the CD4 counts with a correlation coefficient (r) of 0.99 (http://easycalculation.com/statistics/correlation).
A scatter plot of the PIMA CD4 Count versus the BD FACS Count CD4 count was plotted, after which a regression line was added to the plot. The scatter plot indicates a very good correlation as the points are closely clustered around the linear regression line (Fig. 1).
A healthy and HIV-uninfected individual has a CD4 count between 500 and 1200 cells/mm.4 In an infected person, the CD4 cells (absolute numbers of T-helper cells) are attacked by the HIV and their count progressively declines over a number of years2,3 and results in the progressive weakening of the host immune system.
The enumeration of CD4 count has become an essential part of monitoring the course of immunosuppression caused by the HIV and the initiation of antiretroviral therapy.5
Serial measurements of absolute CD4+ T-lymphocyte counts are required to initiate and gauge response to therapy and monitor disease progression. The CD4 cell counts have been traditionally performed based on the principle of flow cytometry using single and dual platform methods. Other methods for CD4 count determinations, such as EIA and micro bead assays, are available and correlate well with flow methods. However, these assays prove to be expensive, as they need a sophisticated laboratory, equipment, and highly skilled technicians. Also, they are out of reach of the primary health care centers, especially in resource poor countries.
Clinicians wishing to test patients for CD4 are faced with the challenge of not only transporting a patient sample to a testing site but also the provision of the CD4 test result back to the patient. Consequently, many patients are lost to follow-up before initiation of antiretroviral therapy, which is a challenge to the scale-up of treatment.4,6
Hence, there is a need for rapid, low-cost, point-of-care CD4 test that would enable clinics to stage patients rapidly on-site after enrolment, which can reduce opportunities for pretreatment and loss to follow-up.7 More patients can be identified as eligible for and initiated with antiretroviral treatment. Point-of-care testing might therefore be an effective intervention to reduce pretreatment loss to follow-up.6
The Alere PIMA CD4 test provides a revolutionary point-of-care solution to the challenge of providing an absolute CD4 count to those previously with restricted access to such testing.
Using a disposable PIMA CD4 cartridge containing sealed reagents, and the portable PIMA Analyser, the Alere PIMA CD4 test delivers an absolute count of T-helper cells from either a fingerprick or venous whole blood sample within 20 minutes as against one-and-a-half hour on the FACS count.
The absolute CD4 cell count obtained using the PIMA system correlated well with those of the FACS Count, with no statistically significant difference and with low bias, for all ranges of the CD4 counts.
The Alere PIMA CD4 test system was found to be a handy and portable user-friendly point of care and system with a performance at par with that of a conventional flow cytometer for absolute CD4 counts. Because it is battery operated, it has a potential for field applicability in high-burden resource-poor countries. The user would find it to be an accurate and cost-effective tool in the management of HIV patients, especially in remote locations or resource limited setups.
1. Sukapirom K, Onlamoon N, Thepthai C, et al.. Performance evaluation of the Alere PIMA CD4 test for monitoring HIV-infected individuals in resource-constrained settings. BioMed Central. J Acquir Immune Defic Syndr. 2011;58(2):141–147.
2. Cheng X, Irimia D, Dixon M, et al.. A microchip approach for practical label-free CD4+ T-cell counting of HIV-infected subjects in resource-poor areas. J Acquir Immune Defic Syndr. 2007;45:257–261.
5. WHO. Rapid Advice: Antiretroviral Therapy for HIV Infection in Adults and Adolescents.
6. Jani IV, Sitoe NE, Alfai ER, et al.. Effect of point-of-care CD4 cell count tests on retention of patients and rates of antiretroviral therapy initiation in primary health clinics: an observational cohort study. Lancet. 2011;378(9802):1572–1579.
7. Larsen CH. The fragile environments of inexpensive CD4+ T-cell enumeration in the least developed countries: strategies for accessible support. Cytometry B Clin Cytom. 2008;74(suppl 1):S107–S116.