As far as we know this is the first study on retention in the DRC across different sites, using a standardized data extraction tool. The overall retention rates in this local NGO supported ART program in DRC were 81.4% (95% CI: 79.3–83.4), 75.2% (95% CI: 72.8–77.3), 65.0% (95% CI: 62.3–67.6) and 57.2% (95% CI: 54.0–60.3) at 6 months, 1 year, 2 years and 3 years respectively. These low retention rates demonstrate that retention is a major challenge. Although these results seem comparable to those from other studies in sub-Saharan Africa settings 
, we need to be cautious in interpreting these numbers. Whereas most of the sub-Saharan countries managed to scale up their coverage of patients on ART (with an average coverage of 36% at the end of 2009) 
, the DRC is lagging behind with a reported coverage of only 12.4% in 2010. 
In other words, these low retention rates are even more sobering when considering the limited scaling up of ART in the DRC. Furthermore these results come from a local NGO program, which might not be representative of the situation in the public sector in the country.
There was a wide variability of retention rates between the different sites, (between 62.1% and 90.6% at 6 months and between 55.5% and 86.2% at 1 year). Retention rates were significantly lower in the 2 semi-urban sites. These 2 centers were smaller treatment centers with smaller number of health care providers and patients in HIV care. These findings contrast somehow with other studies reporting better retention in rural and decentralised sites because of greater access to services and better integration of services. 
Probably other factors contributed to this: these centers did not have access to CD4 cell count, were not participating in the IeDEA Central Africa database (and thus did not receive the same level of support), they also received less supervisory visits. This emphasises the need for timely monitoring of key indicators (such as mortality, retention) and regular supervisory visits for training and mentoring.
Patients who started ART during the scaling up process (2007–2009) were more at risk to be lost to follow-up compared to patients starting ART during the early years (2005–2006), a finding that concurs with results from other studies. 
Rapid scaling-up may have compromised the organisation and quality of care. In the six study sites the number of patients on ART increased from 1570 in 2006 to about 7800 in 2009. This again demonstrates the need for an electronic database system with a user-friendly reporting tool enabling programs to actively and timely track patients not showing up for their scheduled appointment. An active defaulter system will also improve the reliability of mortality data of a cohort. In our study, 25% of patients not retained in the first year consisted of reported deaths, meaning that LTFU was the dominant contributor to attrition. This is consistent with findings from other ART programs in sub-Saharan Africa. 
Other studies have shown that more than 50% of patients LTFU have, in fact, died. 
Due these high mortality rates among patients LTFU after ART, and to avoid overestimation of success of ART programs, it is recommended to use attrition (death and LTFU) instead of mortality only to evaluate the success of programs. 
Male sex, weight below 50 kg and higher WHO stage at initiation were independent risk factors for attrition, a finding that concurs with results from other studies from sub-Saharan Africa. 
Attrition was highest in the first months on ART. This can be explained by the elevated early mortality as demonstrated by others, 
and this in turn is due to the late presentation of patients in an advanced stage. During multivariable analysis CD4 cell count was not an independent risk factor but this could be due to the limited availability of CD4 cell count. The fact that more than half of the patients included in the study did not have a baseline CD4 cell count demonstrates the limited availability of CD4 cell count in the DRC. The limited access to ART and OI drugs for opportunistic infections (OI) in the country have resulted in persisting waiting lists for ART. WHO 
recommends that ART should be started at a CD4 count of 350 cells/µl. However today many treatment centers in DRC are decreasing their threshold for ART even below 200 CD4 cells/µl because of insufficient access to ART. Limited CD4 cell count availability, reluctance to initiate ART without CD4 cell count (despite the WHO guidelines), the cost of laboratory tests and X-rays further hinder the scaling-up of ART in DRC.
Increasing CD4 cell count availability mainly for determining eligibility for ART, and less for clinical monitoring should be one the priorities. The DART study 
showed that a greater public health effect would be gained from widening access to ART rather than providing routine laboratory monitoring for patients already receiving ART. In a resource-limited setting as the DRC, clinical monitoring during the first two years on treatment might be more cost-effective instead of the routine laboratory monitoring which is currently in practice.
Distance or time to travel was not an independent risk factor for attrition in our study, contrary to other studies 
but this could be due to unavailability of this data in two of our study sites.
Limitations of the study are related to the limitations of a retrospective chart review and consist mainly of incomplete data and absence of certain variables at some of the sites. For example more than 10% of data were missing for WHO clinical stage and weight at baseline, numbers that are similar as the findings by May et al. 
The quality of the data varied a lot amongst the sites, Forster et al found that poor quality data was associated with poor retention. 
This was similar in this study, however the sites with lower retention did receive a lot less support in general (funding, clinical mentoring, administrative support).
This study shows that, also in DRC, retention is a major problem, while coverage of patients on ART is still very low.
With the flattening of funding for HIV care and treatment in sub-Saharan Africa, and with decreasing funding worldwide 
, maximizing retention during the much needed scaling-up will even be more important.