The DRS-R-98, a 16-item clinician-rated scale with 13 severity items and 3 diagnostic items, was validated against the Cognitive Test for Delirium (CTD), Clinical Global Impression scale (CGI), and Delirium Rating Scale (DRS) among five diagnostic groups (N=68): delirium, dementia, depression, schizophrenia, and other. Mean and median DRS-R-98 scores significantly (P<0.001) distinguished delirium from each other group. DRS-R-98 total scores correlated highly with DRS, CTD, and CGI scores. Interrater reliability and internal consistency were very high. Cutoff scores for delirium are recommended based on ROC analyses (sensitivity and specificity ranges: total, 91%-100% and 85%-100%; severity, 86%-100% and 77%-93%, respectively, depending on the cutoffs or comparison groups chosen). The DRS-R-98 is a valid measure of delirium severity over a broad range of symptoms and is a useful diagnostic and assessment tool. The DRS-R-98 is ideal for longitudinal studies.
