BACKGROUND: While the benefits for clients collecting antiretroviral therapy (ART) through differentiated service delivery programmes (DSD) have been described, there are limited data on whether DSD indirectly benefits clients ineligible for DSD, by allowing more clinic resources to be redirected towards them. SETTING: De-identified, routinely-collected data from 112 clinics in KwaZulu-Natal, South Africa were analysed. METHODS: Using generalized linear mixed effects regression, we assessed whether the quality of care provided to clients initiating ART (and therefore ineligible for DSD) improved following increases in the proportion of clients in their clinic referred to DSD. Quality-of-care outcomes were the probability of clients having a CD4 count test, having a 6-month viral load (VL) test and being retained for 6 months. RESULTS: Between February 2022 and September 2023, 36,865 clients initiated ART. Among those in each outcome analysis, 77% had CD4 count results, 72% had 6-month VL results, and 70% were retained for 6 months. We found a positive relationship between the clinic DSD referral proportion and test completion among newly initiated clients, although this was only weakly significant for CD4 count; when DSD referrals increased from 20-30%, the probability of having a CD4 count and VL test increased by 0.97% (95% CI: -0.27,2.58%) and 1.35% (95% CI: 0.11,2.95%) respectively. We found no evidence of an association with DSD and retention. CONCLUSIONS: In the first study of this topic, increases in clinic DSD referrals were associated with small improvements in care. With full DSD scale-up, programmatically meaningful effects could be achieved.