Determinants of HIV Testing Uptake Among People Who Use New Psychoactive Substances in Kazakhstan: A Multi-Regional Cross-Sectional Study

Background: New psychoactive substances (NPS) represent an evolving component of global substance use patterns and may contribute to HIV transmission through both injection-related and sexual risk behaviors. In Kazakhstan, where HIV incidence has increasingly shifted toward sexual transmission, evidence on HIV testing among NPS users remains limited. This study examined behavioral, social, and structural factors associated with HIV testing in this population. Methods: A cross-sectional study was conducted among 1500 adults reporting NPS use across six regions of Kazakhstan. Data were collected using structured interviewer-administered questionnaires. The primary outcome was self-reported HIV testing (ever tested: yes/no). Independent variables included sociodemographic characteristics, substance use behaviors, sexual practices, peer communication about HIV, and structural access to prevention services. Univariable logistic regression with Bonferroni correction (p < 0.001) was used for variable screening. Multivariable logistic regression models estimated adjusted odds ratios (AORs) with 95% confidence intervals (CIs). Model discrimination was assessed using the area under the receiver operating characteristic curve (AUC). Results: Overall, 86.7% of participants reported prior lifetime HIV testing. In the multivariable model (n = 1482), older age was associated with higher odds of testing (AOR 1.06 per year; 95% CI 1.04–1.08; p < 0.001). Compared with participants holding a bachelor’s degree or higher, those without a high school diploma had lower odds of testing (AOR 0.50; 95% CI 0.28–0.89). Injectable psychostimulant use was also associated with testing (AOR 1.40; 95% CI 1.21–2.01). Participants who never discussed HIV within peer networks were less likely to have been tested (AOR 0.69; 95% CI 0.49–0.97). Engagement with HIV prevention services (AOR 0.54; 95% CI 0.39–0.75) and use of prevention centers (AOR 0.63; 95% CI 0.45–0.87) were significantly associated with testing. The model demonstrated acceptable discrimination (AUC = 0.725). Conclusions: Lifetime HIV testing uptake among NPS users in Kazakhstan is high but influenced by educational attainment, peer communication, injection practices, and engagement with prevention services. Strengthening integration of prevention services and expanding peer-based outreach may improve equitable access to HIV testing in this population.