ABSTRACT:

Background: Despite the great efforts to expand anti-retroviral therapy (ART) services in Tanzania since 2004, data shows that the proportion of patients on second line is still very low. This may be due to the fact that patients who fail the first line are not recognized in time.In a resource limited country like Tanzania quantification of the human immunodeficiency virus type 1 (HIV-1) RNA levels (viral load) in plasma is limited. This is due to lack of enough health facilities to performreal-time
based PCR assays.This study aimed at evaluating an Ultrasensitivep24 antigen assay as a potential alternative to HIV-1 RNA viral load assay.

Methodology: HIV infected patients attending care and treatment clinics in selected Mwanza city hospitals (Buzuruga, Nyamagana and Sekou-Toure) were recruited. Aseptic venipuncture wasdone to obtain 5mls of blood. This was used for p24 antigen assay, viral load assay and CD4 determination. Laboratory results were then compared to detect the utility of p24 assay compared to real time based PCR assay in establishment of immunological failure.

Results: A total of 270 HIV- infected participants were recruited (192 ART naïve and 78 (29%) on ART). HIV experienced ART had lower median (IQR) p24 antigen level of 3.4 (1.53; 4.43) pg/mL compared to 10.6 (3.34; 39.32) pg/mL median p24 antigen level of HIV ARV naïve. In the period of 6 months and above of being on ARV, 14.5 % of the participants were categorized as immunological failure while virological suppressions was 69.2 %. CD4+ lymphocyte count at recruitment andheat denatured p24 antigen level were significantly correlated with each other (r = -0.38; 95%CI, -0.48; -0.27, p<0.001). The gradual increase of p24 antigen level with time correlated with an increase of proportion of immunological failure. Only CD4+ lymphocyte was highly predicative of subsequent immunological failure. In cox multivariate models the age and CD4+ lymphocyte were factors that were highly predictive of subsequent immunological failure.

Conclusions: p24 antigen level in our study population was well correlated with CD4 lymphocyte count. The rise in p24 antigen levels was correlated with the proportion of immunological failure. Although p24 was not found to be statistically significant predictor of immunological failure but its correlation with CD4 count still makes it a useful indicator of immunological failure. p24 antigen assay can easily be measured in our resource limited environment with minimum challenges.