Table 1.
Characteristics of included studies.
| Author | Year | Country | Ethnicity | Case/Control (n) | Leptin Source | Assay approach | NOS | Study design | PSG type |
|---|---|---|---|---|---|---|---|---|---|
| Ip MS et al. (18) | 2000 | China | Asian | 30/30 | Serum | RIA | 7 | CCS | Lab PSG |
| Phillips BG et al. (19) | 2000 | Poland | Caucasian | 32/32 | Plasma | RIA | 7 | CCS | Lab PSG |
| Ulukavak Ciftci T et al. (20) | 2005 | Turkey | Caucasian | 30/22 | Serum | ELISA | 8 | CCS | Lab PSG |
| Rubinsztajn R et al. (21) | 2005 | Poland | Caucasian | 36/15 | Serum | RIA | 6 | CCS | Lab PSG |
| Barcelo A et al.(obese) (22) | 2005 | Spain | Caucasian | 23/19 | Plasma | RIA | 8 | CCS | Lab PSG |
| Barcelo A et al.(non-obese) (22) | 2005 | Spain | Caucasian | 24/18 | Plasma | RIA | 8 | CCS | Lab PSG |
| McArdle N et al. (23) | 2007 | Australia | Caucasian | 21/21 | Serum | ELISA | 7 | CCS | Portable device |
| Sharma SK et al. (24) | 2007 | India | Asian | 40/40 | Serum | ELISA | 8 | CS | Lab PSG |
| Tokuda F et al.(mild-to-moderate) (25) | 2008 | Japan | Asian | 21/15 | Serum | ELISA | 8 | CCS | Portable device |
| Tokuda F et al.(severity) (25) | 2008 | Japan | Asian | 32/15 | Serum | ELISA | 8 | CCS | Portable device |
| Kapsimalis F et al.(mild-to-moderate) (26) | 2008 | Greece | Caucasian | 26/15 | Serum | RIA | 7 | CSS | Lab PSG |
| Kapsimalis F et al.(severity) (26) | 2008 | Greece | Caucasian | 26/15 | Serum | RIA | 7 | CSS | Lab PSG |
| Makinodan K et al. (27) | 2008 | Japan | Asian | 13/12 | Serum | ELISA | 7 | CCS | Lab PSG |
| Yamamoto Y et al. (28) | 2008 | Japan | Asian | 10/31 | Serum | ELISA | 6 | CSS | Lab PSG |
| Jian Y et al. (29) | 2008 | China | Asian | 68/30 | Serum | RIA | 6 | CCS | Lab PSG |
| Antonopoulou S et al. (30) | 2008 | Greece | Caucasian | 45/25 | Plasma | ELISA | 7 | CCS | Lab PSG |
| Wysocka E et al.(obese) et al. (31) | 2009 | Poland | Caucasian | 18/18 | Serum | ELISA | 8 | CCS | Lab PSG |
| Wysocka E et al.(non-obese) (31) | 2009 | Poland | Caucasian | 18/18 | Serum | ELISA | 8 | CCS | Lab PSG |
| Acioglu E et al. (32) | 2010 | Turkey | Caucasian | 34/19 | Serum | ELISA | 7 | CSS | Lab PSG |
| Ursavas A et al. (13) | 2010 | Turkey | Caucasian | 45/15 | Serum | ELISA | 7 | CSS | Lab PSG |
| Carpagnano GE et al.(obese) (33) | 2010 | Italy | Caucasian | 36/24 | Plasma | ELISA | 7 | CCS | Lab PSG |
| Carpagnano GE et al.(non-obese) (33) | 2010 | Italy | Caucasian | 28/20 | Plasma | ELISA | 7 | CCS | Lab PSG |
| Canapari CA et al. (34) | 2011 | USA | Caucasian | 15/16 | Serum | RIA | 8 | CCS | Lab PSG |
| Basoglu OK et al. (35) | 2011 | Turkey | Caucasian | 36/34 | Serum | ELISA | 8 | CCS | Lab PSG |
| Sanchez-de-la-Torre M et al.(obese) (12) | 2012 | Spain | Caucasian | 10/28 | Plasma | RIA | 7 | CCS | Portable device |
| Sanchez-de-la-Torre M et al.((non-obese) (12) | 2012 | Spain | Caucasian | 21/20 | Plasma | RIA | 7 | CCS | Portable device |
| Matos G et al. (36) | 2013 | Brazil | Latinos | 119/187 | Serum | ELISA | 7 | CCS | Lab PSG |
| Salord N et al. (37) | 2014 | Spain | Caucasian | 26/13 | Serum | ELISA | 8 | CSS | Lab PSG |
| Yosunkaya S et al. (38) | 2015 | Turkey | Caucasian | 31/25 | Serum | ELISA | 7 | CCS | Lab PSG |
| Chihara Y et al. (39) | 2015 | Japan | Asian | 39/15 | Serum | RIA | 8 | CSS | Lab PSG |
| Dubey A et al.(mild) (40) | 2015 | India | Asian | 26/22 | Serum | ELISA | 7 | CSS | Lab PSG |
| Dubey A et al.(moderate-to-severity) (40) | 2015 | India | Asian | 64/22 | Serum | ELISA | 7 | CSS | Lab PSG |
| De Santis S et al. (41) | 2015 | Italy | Caucasian | 26/24 | Serum | ELISA | 7 | CCS | Lab PSG |
| Gaines J et al.(mild) (42) | 2016 | USA | Caucasian | 109/138 | Plasma | ELISA | 8 | CSS | Lab PSG |
| Gaines J et al.(moderate) (42) | 2016 | USA | Caucasian | 44/138 | Plasma | ELISA | 8 | CSS | Lab PSG |
| Kapusuz Gencer Z et al. (11) | 2017 | Turkey | Caucasian | 36/22 | Serum | ELISA | 8 | CCS | Lab PSG |
| Van Eyck A et al.(mild) (43) | 2017 | Belgium | Caucasian | 28/111 | Serum | ELISA | 8 | CSS | Lab PSG |
| Van Eyck A et al.(moderate-to-severe) (43) | 2017 | Belgium | Caucasian | 25/111 | Serum | ELISA | 8 | CSS | Lab PSG |
| Cakir I et al.(mild-to-moderate) (44) | 2018 | Turkey | Caucasian | 11/30 | Serum | ELISA | 7 | CCS | Lab PSG |
| Cakir I et al.(severity) (44) | 2018 | Turkey | Caucasian | 39/30 | Serum | ELISA | 7 | CCS | Lab PSG |
| Ji L et al. (45) | 2019 | China | Asian | 24/24 | Serum | ELISA | 6 | CCS | Lab PSG |
| Sertogullarindan B et al. (46) | 2019 | Turkey | Caucasian | 55/35 | Plasma | ELISA | 8 | CCS | Lab PSG |
| Dalesio NM et al.(non-obese) (14) | 2020 | USA | Caucasian | 9/18 | Plasma | Mass spectrometry | 8 | CCS | Lab PSG |
| Dalesio NM et al.(obese) (14) | 2020 | USA | Caucasian | 13/18 | Plasma | Mass spectrometry | 8 | CCS | Lab PSG |
| Emara TA et al. (15) | 2021 | Egypt | Caucasian | 23/18 | Serum | ELISA | 7 | CCS | Lab PSG |
CSS, cross sectional studies; CCS, case-control studies; CS, cohort studies; PSG, polysomnogram; NOS, Newcastle-Ottawa scale; ELISA, Enzyme linked immunosorbent assay; RIA, Radioimmunoassay; NA, not available.