Global Deterioration Scale

It is a staging instrument, not a scored cognitive test. Instead of administering items and summing points, the clinician forms a global judgment from clinical interview and informant report and matches the patient to one of seven ordered stage descriptions. The result is an ordinal position on the course of dementia rather than a numeric performance score. For this reason the GDS complements, rather than replaces, structured cognitive screens, and it is often used together with one.

Stage 4 is the conventional threshold. Stages 1 to 3 span normal cognition, very mild (often subjective) decline, and mild decline with the earliest objective deficits, none of which meets the bar for dementia. At stage 4 the deficits are clear enough to interfere with everyday activities and to support a clinical diagnosis of dementia, and stages 5 through 7 then track moderately severe, severe, and very severe disease. Recognizing that the lower stages are pre-dementia is important to avoid over-diagnosis.

All three come from Reisberg's group and were designed to work together. The GDS provides the overarching seven-stage global picture, the Brief Cognitive Rating Scale rates specific cognitive axes, and the Functional Assessment Staging Tool subdivides the more severe stages by concrete functional milestones such as dressing, continence, and speech. In advanced dementia, where cognitive testing is no longer feasible, clinicians often rely on FAST sub-stages to grade severity, while the GDS remains the common reference frame across the whole course.