Medical card holders accounted for the majority of patients treated at 57 acute public hospitals across the country last year.
The research carried out by the ESRI examined activity in 57 public hospitals participating in the hospital in-patient inquiry scheme.
Figures released by the ESRI on behalf of the HSE also show that 83% of total discharges were public patients, that's a 6% increase since 2011.
The number of private patient discharges has been trending downwards since 2008.
There has also been a drop in the length of time people stay in hospitals.
The average length of stay in 2012 was 4.1 days which is a decrease of almost 5% since 2011.
The average acute in-patient length of stay ranged from 3.9 days in the HSE South area to 4.2 days in Dublin North East.
Professor Miriam Wiley, Head of the Health, Research and Information Department at the ESRI, says the figures are in line with international trends.