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) hospitalisation(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 enhance 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 specialised equipment, this finding may provide useful in clinical practise.
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.