Table 1. Main characteristics of the studies included in this meta-analysis[20–27].

Study	Year	Total number	Frailty definition	AKI definition	Risk ratio for AKI	Risk ratio for mortality	Quality assessment
Green et al[20]	2012	159	Frailty score, based on gait speed, grip strength, serum albumin and activities of daily living status, > 5	Acute kidney injury stage 2 or 3 according to VARC-2 definition	1.10 (0.21–5.60)	3.51 (1.43–8.62)	S 4, C 0, O 3
Stortecky et al[21]	2012	256	BMI < 20 kg/m2	Acute kidney injury stage 3 according to RIFLE definition	1.35 (0.13–13.56)	2.43 (0.92–6.39)	S 4, C 0, O 3
Puls et al[22]	2014	300	Katz index < 6	Acute kidney injury according to modified RIFLE definition	AKI; 1.23 (0.76–2.00), AKI stage 3; 2.23 (1.12–4.47)	2.67 (1.7–4.3)	S 4, C 0, O 3
Green et al[23]	2015	244	Frailty score, based on gait speed, grip strength, serum albumin and activities of daily living status, ≥ 6	Renal failure requiring dialysis	1.62 (0.58–4.49)	2.50 (1.40–4.35)	S 4, C 0, O 3
Yamamoto et al[24]	2015	777	BMI < 20 kg/m2	Acute kidney injury according to VARC-2 definition	0.84 (0.26–2.70)	0.68 (0.29–1.61)	S 4, C 2, O 3
Alfredson et al[25]	2016	8,039	5-m gait speed < 10 s	Acute kidney injury according to VARC-2 definition	1.18 (0.91–1.53)	1.35 (1.01–1.80)	S 4, C 0, O 3
Koifman et al[26]	2016	491	BMI < 20 kg/m2	Acute kidney injury stage 2 or 3 according to VARC-2 definition	1.04 (0.30–3.94)	2.45 (1.26–4.75)	S 4, C 0, O 3
Saji et al[27]	2016	232	The lowest tertile of normalized psoas muscle mass (cross-sectional areas of the psoas muscle at the L4 vertebra level measured by CT and normalized to body surface area)	Acute kidney injury stage 2 or 3 according to AKIN definition	1.20 (0.52–2.80)	2.30 (1.09–4.86)	S 4, C 0, O 3

Abbreviation: AKI, acute kidney injury; AKIN, Acute Kidney Injury Network; BMI, body mass index; S, selection; C, comparability; O, outcome; VARC, Valve Academic Research Consortium.