CHAPTER 25: FUNCTIONAL ASSESSMENT STAGING SCALE (FAST)

Description

The Functional Assessment Staging (FAST) by Reisberg (1988) is an observational rating tool developed to quantify the clinically identifiable stages of neurocognitive disorders (NCD) of the Alzheimer’s and related types as well as age associated impairment. It is a procedure that describes a continuum of 16 successive stages and substages (from normal to severe) experienced by individuals with cognitive impairment through examination of the presence or absence of specific behaviors associated with decline. The concept of staging employed by FAST is unique in that it can identify pre-morbid and potentially manifest conditions associated with the evolution of the disease process, which is thought to follow a specific course, as well as the ability to track the latter stages of NCD dementias when most mental status assessments are no longer valid (Reisberg et al., 2011). FAST categorizes individuals into a 7-point rating scale (1 to 7) where a lower score is indicative of less impairment. Stages 6 and 7 are further divided into 11 subscales (6a to 6f and 7a to 7e) allowing the clinician to further enumerate the perceived phenomenon they are witnessing, thus allowing the clinician an important diagnostic and differential diagnostic tool (Auer & Reisberg, 1997). If the client is familiar, assessment can be as little as 5 minutes.

Psychometrics

FAST scale reliability studies have demonstrated rater consistency of r = 0.86 and rater agreement of r = 0.87, whereas the coefficient of reproducibility, a measure of uni-dimensionality, was 0.99 (a reproducibility higher than 0.9 indicates a valid scale; Sclan & Reisberg, 1992). When compared with the Ordinal Scales of Psychological Development (OSPD), FAST correlated significantly at –0.79 and levels ranged from –0.60 to –0.79 between individual FAST/OSPD subtests (Sclan & Reisberg, 1992). Another study found that the correlation between FAST and the Global Deterioration Scale (GDS) was 0.9 The correlation between the FAST and the Mini-Mental State Exam (MMSE) was observed to be 0.8 (Auer & Reisberg, 1997). A significant correlation between the FAST stage and the basic age (BA) value on the Tanaka–Binet intelligence scale (TB scale) was also observed (r = 0.85); however, the TB scale could not assess basic age through stage 7 because of floor effects (Masumi et al., 2003). A subsequent study by its authors suggest that the FAST staging procedure has the ability to account for more than twice the variance in temporal course explained by conventional mental status assessments and when used in conjunction with the GDS it can account for approximately three times the variance explained by the MMSE alone (Auer & Reisberg, 1997). Finally, the predictive value of FAST was discussed by Komarova and Thalhauser (2011) where they noted the presence of large variations in disease progression in a cohort of 648 individuals and found that for stage 4 the typical amount of time person with NCD Alzheimer’s spent was 2.1 years, stage 5, 1.8 years, and for 6 it was 4.3 years.

Advantages

The FAST scale is a simple observational tool that requires no special training and there is a good amount of research in support of its use in clinical practice. Another advantage of the FAST staging system is that it allows the assessment and staging of the various types of NCD throughout the entire range of the disablement process from normal aging to very severe, end-stage symptoms. This allows the designation of disease progress over time as well as the ability to determine if any changes in a person’s condition are due to NCD or other conditions such as medication because NCD stages, as they relate to the FAST scale, are thought to occur in sequence (Komarova & Thalhauser, 2011). The FAST scale has shown to correlate well with other measures and is considered to be concordant with the GDS from which it was derived. Finally, the fact that FAST delineates 5 functional sub-stages between stage 6 and stage 7 is advantageous because many conventional measures experience floor/ceiling effects in the final 6 to 8 substages of the disease process that FAST is able to differentiate.

Disadvantages

The FAST scale is not designed as a classical standardized assessment per se, and is dependent on skilled observation and knowledge of the disease process in order to correctly classify an individual along its continuum; thus, an understanding of each level’s inclusion/exclusion criteria is necessary. The rater may find stages 6 and 7, which have 11 substages, particularly difficult when trying to evaluate the subtle nuances and markers of the disease toward the end stages.

Administration

The FAST scale is an observational tool in which a person’s cumulative score is calculated by increasingly discerning the presence or absence of manifestations of neurocognitive impairment typical of that found in NCD of Alzheimer’s and related types. Table 25-1 is an example of the 7 basic stages (excluding the 11 sub-stages between 6 and 7). More detailed scales and explanations can be found elsewhere or in Reisberg’s 1988 article from Psychopharmacology Bulletin.

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