UTILITY AND CONSTRUCT VALIDITY OF THE SARC-F INSTRUMENT IN PATIENTS WITH NON-DIALYSIS CKD

Abstract BACKGROUND AND AIMS Protein energy wasting (PEW), and cachexia is common in people with non-dialysis chronic kidney disease (CKD) and it can lead to reduced muscle mass and physical function (also termed sarcopenia). There are no well-established, simple and reliable methods for identifying cases of sarcopenia. The SARC-F questionnaire is recommended to pre-screen for sarcopenia. However, the utility and construct validity of the SARC-F in nondialysis CKD patients is yet to be investigated, particularly whether the SARC-F can correctly identify poor physical performance—a key element of the sarcopenia phenotype in patients with CKD. The aim of the present analysis was to establish the utility and construct validity of the SARC-F in people with CKD, as well as to investigate which items of the SARC-F are the most impactful in predicting sarcopenia, assessed by the 60 second sit to stand test (STS60). METHOD 146 non-dialysis CKD patients (94 (64%) males, age 60.63 (±14.4) years, eGFR range 15–59 mL/min/1.73 m²) filled out the SARC-F questionnaire and completed the 60-s sit to stand test (STS60), a well-established assessment of physical performance. There are five SARC-F components: ‘strength’, ‘assistance with walking’, ‘rise from a chair’, ‘climbing stairs’ and ‘falls’. The scores range from 0 to 10, with 0 to 2 points for each component. A score ≥4 is predictive of sarcopenia and poor outcome. Score distribution was explored via frequency analysis to establish floor or ceiling effect(s) (≥15%). Construct validity between the SARC-F components and STS60 performance was assessed by Spearman's rank correlation. General linear modeling was used to determine significant predictors for STS60 performance. Linear regression was used to investigate whether SARC-F total scores were a predictor for STS60 performance. RESULTS Sarcopenia was present in 16 out of the 146 (10.9%) patients. Floor and ceiling effects of each SARC-F item, and SARC-F total scores, are presented in Figure 1. All items as well as SARC-F total scores showed a floor effect with more than 50% of patients scoring ‘None’ on each item and thus had ‘0’ in total scores (Figure 1). The ‘climbing stairs’ item displayed the highest (r = −0.584, P < 0.001) association with STS60 performance, followed by SARC-F total scores (r = −0.583, P < 0.001), ‘strength’ (r = −0.470, P < 0.001), ‘assistance in walking’ (r = −.457, P < 0.001), ‘rise from a chair’ (r = –0.424, P < 0.001) and ’falls’ (r = –0.282, P = 0.002). The ‘climbing stairs’ item was a significant predictor for STS60 performance (Table 2), and SARC-F total scores were a significant predictor for STS60 performance (P < 0.001, R = 0.375, Β = −0.48–26.891). CONCLUSION The present data suggest that the ‘climbing stairs’ component of the SARC-F, as well as total SARC-F scores are valid predictors for lower body physical performance. This suggests that the SARC-F has limited ability to screen for lower body strength, and thus it may not be adequate to screen for sarcopenia. These results could be explained by the significant floor effect exhibited. It is also surprising that the ‘Rise from a chair’ item did not show higher association with, and predictive ability for STS60 performance. This item showed the second to highest floor effect which could contribute to this result. Thus, caution should be applied when using the SARC-F for sarcopenia screening especially in clinical populations where protein energy wasting may be present.