Background: HIV treatment centres register HIV positive patients, specially trained doctors prescribe Antiretroviral Therapy to the selected cases that fulfill the criteria for initiation of HAART.

Aim: To establish predictive markers of failure of 1^st line ART in HIV positive patients on first line ART under treatment in HIV Treatment Centre of PIMS Islamabad.

Study design: Retrospective case control study.

Methodology:  Retrospective case control study done at HIV Treatment Centre at PIMS Islamabad. Cases were patients who failed 1^st line ART and started on second line ART from November 2005 to June 2020. Patients responding well to first line ART since more than five years or more were taken as controls. Various factors were analyzed in both groups and compared to find their level of significance. Data was analyzed by SPSS software, version 25 as qualitative variables were expressed as frequencies and percentages.

Results: CD4 count of all 38 patients was below 300 on diagnosis. In 21 patients (55.3%) CD4 count initially increased but there was no rise in CD4 count in 17 patients (44.7%) after start of 1^st line ART.

Conclusion: We concluded that CD4 count is one of the most important predictive markers in success or failure of ART. Rising number of CD4 count on follow up visits gives a strong indication that patient is responding well to the prescribed treatment and is likely to benefit from the current regimen of ARVs for a longer period in future.

Keywords: Predictive Markers, CD4 count, Viral Load, HIV, ART, Compliance and Co-morbidities.