TABLE 1.

Characteristics of the negative observational studies regarding the relationship of Klotho with kidney function.

First author	Year	Country	N	Age	Samples	eGFR	sKlotho level	Klotho and eGFR	NOS
Desbiens	2022	Canada	159 non-CKD	53 (46–60)	Plasma	90	677 (565–877) ▲	Similar levels of sKlotho between the two groups.	6 stars
			153 CKD	64 (59–67)		55	662 (543–831)
Bob	2018	Romania	63 DKD	58.13 ± 12	Serum	65.2 ± 32.5	326.36 ± 246.78 ▲	sKlotho level did not correlate with eGFR	6 stars
Scholze	2014	Denmark	24 CKD	68 (59–75)	Serum	31 (21–55)	236 (193–291) ▲	sKlotho concentrations did not differ among CKD stages
Sari	2017	Turkey	76 ADPKD	50.96 ± 15.59	Serum	57.24 ± 33.80	2.92 (0.99–21.97) ★	sKlotho levels were negatively correlated with eGFR	4 stars
			32 controls	49.53 ± 7.32		90.15 ± 20.71	2.04 (0.95–19.98)
Hage	2014	France	60 CKD	46.7 6 ± 16.6	Serum	71.1 ± 29.2	478 (348–658) ▲	sKlotho is not related to kidney function
Devaraj	2012	United States	61 CKD	55 ± 17	Serum	CKD1 or CKD3	67 (43, 119) vs108 (66, 182) ★	sKlotho was increased in CKD and was decreased in diabetics	4 stars
			82 diabetics	37 ± 12		Normal eGFR	81 (45, 141) vs 35 (15, 58) ★
Seiler	2013	Germany	321 CKD	65.5 ± 12.1	Plasma	43.8 ± 15.6	538 (450–666) ▲	sKlotho level not differ across CKD stages.	8 stars
Akimoto	2012	Japan	131 CKD	56 ± 18	Serum	46.3 ± 37.5	759.7 (579.5–1,069.1) ▲	Urinary excreted Klotho, not serum Klotho levels associated with eGFR	5 stars

CKD, chronic kidney disease; N, number; DKD, diabetic kidney disease; ▲, pg/ml; ★, ng/ml; ADPKD, autosomal dominant polycystic kidney disease; eGFR, estimated glomerular filtration rate; NOS, Newcastle–Ottawa scale