Abstract
BackgroundAccurate, inexpensive point-of-care CD4+ T cell testing technologies are needed that can deliver CD4+ T cell results at lower level health centers or community outreach voluntary counseling and testing. We sought to evaluate a point-of-care CD4+ T cell counter, the Pima CD4 Test System, a portable, battery-operated bench-top instrument that is designed to use finger stick blood samples suitable for field use in conjunction with rapid HIV testing.MethodsDuplicate measurements were performed on both capillary and venous samples using Pima CD4 analyzers, compared to the BD FACSCalibur (reference method). The mean bias was estimated by paired Student's t-test. Bland Altman plots were used to assess agreement.Results206 participants were enrolled with a median CD4 count of 396 (range; 18–1500). The finger stick PIMA had a mean bias of −66.3 cells/µL (95%CI −83.4−49.2, P<0.001) compared to the FACSCalibur; the bias was smaller at lower CD4 counts (0–250 cells/µL) with a mean bias of −10.8 (95%CI −27.3−+5.6, P = 0.198), and much greater at higher CD4 cell counts (>500 cells/µL) with a mean bias of −120.6 (95%CI −162.8, −78.4, P<0.001). The sensitivity (95%CI) of the Pima CD4 analyzer was 96.3% (79.1–99.8%) for a <250 cells/ul cut-off with a negative predictive value of 99.2% (95.1–99.9%).ConclusionsThe Pima CD4 finger stick test is an easy-to-use, portable, relatively fast device to test CD4+ T cell counts in the field. Issues of negatively-biased CD4 cell counts especially at higher absolute numbers will limit its utility for longitudinal immunologic response to ART. The high sensitivity and negative predictive value of the test makes it an attractive option for field use to identify patients eligible for ART, thus potentially reducing delays in linkage to care and ART initiation.
Highlights
[3] Initiating antiretroviral therapy (ART) in asymptomatic patients with higher CD4+ T cell counts who may not qualify by clinical criteria is desirable as this avoids both morbidity and mortality. [4,5] Eligibility for ART is very difficult to assess by clinical criteria only; many patients eligible by CD4 T cell criteria may not receive medication if clinical signs and symptoms only are used. [6,7]
Performance of Pima CD4 analyzer Duplicate measurements were performed on venous blood samples using two different Pima CD4 analyzers on 206 participants
The mean bias of the capillary testing was 266.3 cells/ mL (95%CI 283.4249.2, P,0.001) overall for the 176 paired samples; the bias was smaller at lower CD4 counts (0–250 cells/ mL) with a mean bias of 210.8 (95%CI 227.32+5.6, P = 0.198), and much greater at higher CD4 cell counts (.500 cells/mL) with a mean bias of 2120.6 (95%CI 2162.8, 278.4, P,0.001). (Table 1) The correlation coefficient between 176 capillary and BD FACSCalibur paired tests was 0.86 (P,0.001)
Summary
The availability of highly active antiretroviral therapy (ART) to the developing world has been life-saving and led to remarkable reversals in mortality rates and opportunistic infection incidence rates. [1,2] According to the WHO classification adopted by most countries in Sub-Saharan Africa, clinicians base the decision to initiate antiretroviral therapy (ART) on CD4+ cell count or WHO stage IV status criteria. [3] Initiating ART in asymptomatic patients with higher CD4+ T cell counts who may not qualify by clinical criteria is desirable as this avoids both morbidity and mortality. [4,5] Eligibility for ART is very difficult to assess by clinical criteria only; many patients eligible by CD4 T cell criteria may not receive medication if clinical signs and symptoms only are used. [6,7].CD4+ T cell counts often need to be done at higher-level health centers with functional labs and adequate power source, or at reference regional labs. [1,2] According to the WHO classification adopted by most countries in Sub-Saharan Africa, clinicians base the decision to initiate antiretroviral therapy (ART) on CD4+ cell count or WHO stage IV status criteria. [3] Initiating ART in asymptomatic patients with higher CD4+ T cell counts who may not qualify by clinical criteria is desirable as this avoids both morbidity and mortality. [8] Due to limited laboratory capacity, access to diagnostic testing is inadequate, and is often non-existent in rural settings. Inexpensive point-of-care CD4+ T cell testing technologies are needed that can deliver CD4+ T cell results at lower level health centers or community outreach voluntary counseling and testing. We sought to evaluate a point-of-care CD4+ T cell counter, the Pima CD4 Test System, a portable, battery-operated bench-top instrument that is designed to use finger stick blood samples suitable for field use in conjunction with rapid HIV testing
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