The recent DSM-5 criteria for delirium can lead to different rates of delirium and different case identification.

The aims of this study were to determine how the new DSM-5 criteria might differ from the previous DSM-IV in detecting rates of delirium in elderly medical inpatients and to investigate the agreement between different methods, including the DSM III, DSM III-R, DSM-IV and DSM-5 criteria.

Prospective, observational study of elderly patients aged 70+ admitted under the acute medical teams in a regional general hospital. Each participant was assessed within 3 days using the DSM-5, and DSM-IV criteria plus the DRS-R98, CAM and MoCA scales.

The studied sample included 200 patients. The prevalence rates of delirium for each diagnostic system/scale were respectively for DSM-5 n=26 (13.0%), DSM-IV n=39 (19.5%), DRS-R98 n=27 (13.5%) and for CAM n=34 (17.0%). Using tetrachoric correlation coefficients the agreement between DSM-5 and DSM-IV was statistically significant (rhotetr=0.64, SE= 0.1, p<0.0001). Similar significant agreement was found between the four methods.

DSM-IV identifies more delirium cases compared to any other method and DSM-5 is the more restrictive. These classification systems identify different cases of delirium. This could have clinical, financial and research implications. However, both classification systems (and their antecedents) have significant agreement in the identification of the same concept (delirium). Clarity of diagnosis is required for classification but also has implications for prediction of outcomes, further research looking at outcomes could assist a more in depth evaluation of the DSM-5 criteria.