Background: Timely outpatient follow-up and readmission after discharge are common quality indicators in psychiatric care, but their association varies in previous research. We aimed to examine whether the impact of outpatient follow-up and other factors on readmission risk evolves over time in people with non-affective psychotic disorder (NAP).

Methods: The Finnish Quality of Care Register includes all people diagnosed with NAP since January 2010. Here, we followed patients with a hospital discharge between 2017 and 2021 until readmission, death, or up to 365 days. Time of the first outpatient follow-up appointment, length of stay (LOS), number of previous hospitalizations, psychosis diagnosis, substance use disorder (SUD), residential status, economic activity, gender, age, year, and region were included. Follow-up time was divided into five periods: week 1, weeks 2-4, weeks 5-13, weeks 14-25, and weeks 26-52, and each period was analyzed separately with Cox regression.

Results: Of the 29 858 discharged individuals, 54.1% had an outpatient follow-up within a week. A total of 10 623 (35.6%) individuals were readmitted. Short LOS increased the readmission risk in the first four weeks, whereas lack of outpatient follow-up raised the risk (adjusted HRs between 1.15 (95% CI 1.04-1.26) and 1.53 (1.37-1.71) in weeks 5-52. The number of previous hospitalizations remained a consistent risk factor throughout the follow-up, while SUD increased risk after 4 weeks and living without family after 13 weeks.

Conclusions: Risk factors of readmission vary over time. These temporal patterns must be considered when developing outpatient treatment programs.