The diagnostic value of the Short Physical Performance Battery for sarcopenia

Sarcopenia, the progressive loss of muscle mass, strength and function, associates with falls, fractures, disability and mortality [1]. As a result of these adverse outcomes, sarcopenia was added to the International Classification of Diseases (ICD-10), allowing for its diagnosis and management in clinical practice [2]. Currently, several definitions exist for the diagnosis of sarcopenia, with each presenting their own diagnostic criteria. These include the European Working Group on Sarcopenia in Older People (EWGSOP1 and 2), [3, 4] Sarcopenia Definition and Outcomes Consortium (SDOC), [5] International Working Group on Sarcopenia (IWGS) [6] and the population specific Asian Working Group on Sarcopenia (AWGS) [7]. In regards to the EWGSOP definition, its most recent update (EWGSOP2) [4] proposed new cut-points and a screening process beginning with the use of the SARC-F [8] for case finding. With these new cut-points and alternate assessments, wide variations in prevalence from 5 to 26% have been reported, [9] which hinders the diagnosis and management of older adults at risk.

Diagnosing sarcopenia involves assessment of muscle mass, strength, and/or physical performance. In the EWGSOP definitions, dual x-ray absorptiometry (DXA) is recommended for the assessment of appendicular lean mass (ALM), corrected for height squared (h²). Meanwhile, handgrip strength and gait speed are favored for assessment of muscle strength and physical performance, respectively. However, substitute measures are also proposed including the sit to stand test (alternate for handgrip strength), the timed up and go (TUG) test, and the Short Physical Performance Battery (SPPB) as alternatives for gait speed.

Of these measures, the SPPB assesses muscle strength, balance and mobility via five timed components, all of which are quick, easy to administer, and don’t require any specialized equipment [10]. As such, we sought to examine the diagnostic value of the SPPB for sarcopenia. This was carried out by first identifying the prevalence of sarcopenia using EWGSOP1 and EWGSOP2 definitions. Upon doing so, the diagnostic value of the SPPB in characterizing individuals with sarcopenia will be evaluated. Finally, cut-points for sarcopenia using the SPPB score will be identified and compared to those currently recommended.

This was a cross-sectional study of 294 community-dwelling older adults based in Melbourne, Australia. Participants attending the falls and fractures clinic for clinical assessment between 2016 and 19 were included. Participants fulfilled the following criteria: aged over 65 years with a history of falls or at risk of falls, ability to mobilize independently with or without the use of gait aids, and no history of cognitive impairment. This study was approved by the Western Health local Human Ethics Research Committee (DB2017.13 and QA2018.80–46,205).

We examined the diagnostic value of the SPPB alone and in combination with ALM/h² in diagnosing sarcopenia in community-dwelling older adults. We characterized the sensitivity and specificity of currently recommended cut-points, in addition to new cut-points based on our study population, and found two main findings. Firstly, the SPPB alone resulted in moderate diagnostic value but increased to an excellent level when combined with DXA measured ALM/h². This was regardless of which definition (EWGSOP1 or EWGSOP2) was employed. Secondly, the currently recommended SPPB cut-point of ≤8 showed high sensitivity for sarcopenia, however, a more conservative cut-point of ≤6 provided the greatest specificity. It therefore appears that the SPPB represents an objective screening tool to diagnose those at risk of sarcopenia.

The SPPB has been used to monitor physical performance in both healthy community-dwelling older adults as well as hospitalized patients [17‐20]. This measure is advantageous in that minimal equipment is required to perform the test, and objective data is provided on muscle strength, gait speed and standing balance. In addition, specific components of the SPPB can independently predict the risk of declines in activities of daily living, [21] falls, [22] hospitalization [23] and mortality [23]. Furthermore, the SPPB can be used as a sensitive monitoring tool for lower limb physical performance with a change of 1 point considered clinical significant [24]. These factors place the SPPB as an ideal tool for the diagnosis of sarcopenia in clinical settings and subsequent monitoring of resistance exercise (RE) interventions which are, at present, the most efficacious treatment for this muscle disease [25]. While other tools such as handgrip strength are reliable, easy to administer and a good marker of whole-body strength, they are poor responders to RE interventions [26]. Thus, the strength component of the SPPB should be assessed by sit to stand time, which is a reliable marker of lower limb strength and is sensitive to change [4].

Our findings show the SPPB displayed acceptable diagnostic value for sarcopenia. When employing the most common cut-points of ≤6, sensitivity and specificity was 65 and 63%, respectively. This cut-point has been associated with more than 3-fold likelihood of recurrent falls for both men and women, [27] one of the primary adverse outcomes of sarcopenia. Indeed, those diagnosed as sarcopenic (using the EWGSOP1) reported a 3-fold increased risk of falls compared to non-sarcopenic adults [28]. When increasing this cut-point to ≤8, the sensitivity and specificity increased to 100 and 41%, respectively. In line with this, this is the cut-point recommended for poor physical performance by the EWGSOP criteria. Despite the excellent sensitivity, the poor specificity of this cut-point indicates that the SPPB cannot be solely used for the diagnosis of sarcopenia.

Highly sensitive tests have been proposed as ideal tools for screening purposes, allowing for the early identification and initiation of treatment [29]. Meanwhile, high specificity has been reported as the key diagnostic factor for a disease, with a combination of high sensitivity/low specificity and low sensitivity/high specificity test an ideal method to address false positives [29]. Using this model, the SPPB displays high sensitivity and represents the ideal screening tool for sarcopenia. Alternately, the SARC-F tool has consistently shown high specificity in numerous studies [30, 31] and may therefore facilitate the diagnostic process. This combined approach represents an area for further research given the potential to enhance clinical care.

Sarcopenia in its current form includes the assessment of muscle strength, mass, and physical performance. However, whilst measures of strength and physical performance have shown links to adverse outcomes of sarcopenia, the same relationship is not observed with ALM [32, 33]. Our findings corroborate previous studies which have shown the disconnect between measures of muscle strength and physical performance and muscle mass. This is represented by the poor to acceptable AUC when using the SPPB as an independent diagnostic tool. However, a combination of SPPB with ALM/h² resulted in increased AUC, matching well with both initial and revised EWGSOP sarcopenia criteria, with the highest diagnostic value evident using the sit to stand test combined with ALM/h² and either gait speed or SPPB. This was somewhat expected given both the sit to stand test and gait speed are already components of the SPPB. However, it was surprising to observe that the combination of SPPB and ALM/h² yielded an increased AUC for all the other diagnostic criteria proposed by EWGSOP2. Given the SPPB is a tool which can be easily implemented into the routine care of patients without a need for specialized equipment, this finding may provide useful in clinical practice.

In the current study, we diagnosed participants presenting with severe sarcopenia which is a strength given that our previous findings showed that the severity of sarcopenia was the driving factor that increased falls and fractures [34]. Studies assessing the impact of sarcopenia in modulating balance performance are required to further efforts in developing interventions. The findings of the present study should also be taken in context of the limitations. Firstly, our population, although community-dwelling, reported a history of falls and/or fractures. Therefore, results may have been biased given that these participants are at increased risk for sarcopenia. Secondly, the cross-sectional nature of our study limits our findings as we are unable to determine whether longitudinally the participants classified as sarcopenic experienced adverse outcomes such as falls. Employing a longitudinal study design would have strengthened the findings.

This study provides an insight into the use of the SPPB for diagnosing sarcopenia according to the initial and revised EWGSOP definitions. Despite the acceptable diagnostic value, no cut-points could be determined which provided high sensitivity and specificity. However, a cut-point of ≤8 in the SPPB showed high sensitivity. Therefore, the SPPB may be used as a screening tool for sarcopenia to trigger further investigations and early intervention. The combination of the highly sensitive SPPB with a highly specific test may prove to be of great use to clinicians for diagnosing and treating sarcopenia, however, requires further investigation in longitudinal trials.