Results from a study evaluating two assays that dramatically lower the cost and difficulty of Aids diagnosis and treatment monitoring were presented at Aids conference
Data from three separate study sites showed that results obtained using the Guava EasyCD4 and EasyCD8 assays for the enumeration of human CD4+ T cells and CD8+ T cells showed excellent correlation with the standard, clinically approved BD Multitest (flow cytometry) assay.
Moreover, assay reproducibility both within-site and between-sites for the Guava assays was reported as 'excellent'.
Study results were provided by investigators from the University of California, San Francisco (UCSF), the Gladstone Institute of Virology and Immunology, California Department of Health Services, and Guava Technologies. They were presented at the satellite symposium organised by the Forum for Collaborative HIV Research and entitled 'HIV Monitoring Technologies for Resource-Limited Settings'. "With many resource-limited areas of the world now gaining access to more affordable anti-retroviral therapies, simpler and less costly methods of monitoring treatment - including absolute CD4+ and CD8+ T cell counts - are urgently needed," said Barry Bredt, director of core laboratories, General Clinical Research Center, UCSF/San Francisco General Hospital.
"Our results suggest that the EasyCD4 and EasyCD8 assays represent good lower cost alternatives to approved flow cytometry methods of CD4+ and CD8+ T cell enumeration.
The Guava assays offer comparable accuracy and reproducibility to the flow cytometry-based method, but are much simpler and more affordable to use".
Absolute CD4+ and CD8+ T cell counts are measurements used to monitor disease progression in HIV/Aids patients, to determine when to begin treatment with antiretroviral drugs and to monitor a patient's response to treatment.
In resource limited countries, the cost of commercially available CD4 diagnostic testing, whether by 'gold standard' flow cytometry or less accurate manual microscopy-based methods, has remained very high.
The Guava EasyCD4 system can dramatically change that and potentially enable improvements in quality of care and even quality of life for the millions of HIV+ patients in these countries.
Study design and results.
The investigators collected blood samples from volunteers and delivered them to each of the participating laboratories within four hours.
Each site tested each specimen by the EasyCD4 and EasyCD8 methods in triplicate.
In addition, a tube of matched blood was analysed by the predicate BD Multitest method at the UCSF clinical laboratory.
A plot of percent difference between EasyCD4 and EasyCD8 methods and the Multitest method showed no trends in bias across the observed range.
The median percent differences for the three sites ranged for CD4 from -1.8% to 8.3% and CD8 from -13.1% to -8.6%.
Similarly the median between-site variability of the EasyCD4 and EasyCD8 was calculated to be 10.6% and 10.8% respectively.
To estimate within-site variability, %CVs (coefficient of variation) were calculated using the three EasyCD4 and EasyCD8 replicates at each site and were reported to be 4.1% to 5.6% and 4.5 % to 5.1%, respectively.
Correlation of both the EasyCD4 and EasyCD8 assays with the BD Multitest assay and inter- and intra-site reproducibility were excellent.
A small negative bias (approximately 10%) between the EasyCD8 and BD Multitest assay was observed.
Guava Technologies provided financial support for the study.
