Table 1.

The clinical research on the relationship between blood Metrnl and type 2 diabetes.

Authors/year	Sample size	Included criteria	Conclusion
Lee et al. (2017) [21]	139 subjects (47 subjects with normal glucose tolerance, 46 subjects with prediabetes, and 46 newly diagnosed T2D patients)	Individuals with type 1 diabetes, gestational diabetes, active hepatitis/liver cirrhosis, chronic renal failure while on hemodialysis, congestive heart failure, or other major diseases were excluded	Serum Metrnl levels were significantly lower in subjects with newly diagnosed diabetes compared with those without diabetes
Dadmanesh et al. (2018) [14]	170 subjects (66 patients with CAD, 63 T2D patients and 41 controls)	Patients with >70% stenosis in at least one coronary artery were diagnosed as CAD. Participants with history and evidence of stroke, myocardial infarction, etc. or using thiazolidinedione family drugs were excluded	Serum Metrnl levels were lower in CAD and T2D patients compared to the control group
Zheng et al. (2018) [22]	20 subjects (11 healthy controls, 9 patients with newly diagnosed T2D)	No other major diseases and treatment	Circulating Metrnl in people with newly diagnosed T2D was lower
Chung et al. (2018) [13]	800 subjects (400 patients with T2D and 400 non-diabetes)	Over 40 years of age without history of cardiovascular disease, without stage 2 hypertension, malignant disease, severe renal or hepatic disease	Blood Metrnl increased in patients with T2D
AlKhairi et al. (2019) [20]	228 subjects (124 non-diabetes [73 non-obese and 51 obese] and 104 T2D [38 non-obese and 66 obese])	BMI > 30 kg/m2 were considered obese; Morbidly obese patients (BMI > 40 kg/m2) or subjects taking medication or supplements known to influence body composition or bone mass were excluded	Blood Metrnl increased in T2D and obesity
Wang et al. (2019) [11]	160 subjects (40 subjects with normal glucose tolerance, 40 subjects with impaired fasting glucose, 40 subjects with impaired glucose tolerance, and 40 patients newly diagnosed T2D)	Patients with previously diagnosed T2D, other types of diabetes, other major diseases, and medication history including the use of antidiabetics, statins, diuretics, corticosteroids, estrogen and progestin were excluded	Blood Metrnl was highest in patients with T2D and significantly increased in patients with prediabetes compared with individuals with normal glucose tolerance
El-Ashmawy et al. (2019) [23]	260 subjects (89 subjects with normal glucose tolerance, 77 subjects with glucose tolerance impairment and 94 with T2D)	BMI < 35 kg/m2; age between 20 and 75 years; no other CVD; no history of malignancy or recent infection; no history of taking antidiabetic medications, concomitant medications such as systemic steroids, cholestyramine, statins, diuretics, β-blockers or oral anticoagulants	Serum Metrnl levels decreased in patients with T2D versus subjects with normal glucose tolerance
Wang et al. (2019) [27]	89 subjects (59 T2D with durations ≥ 1 year and 30 healthy participants)	Patients with other types of diabetes and other major diseases were excluded	Blood Metrnl increased in patients with T2D. No relationship between Metrnl level and obesity-related indicators

T2D type 2 diabetes, CAD coronary artery disease, CVD cardiovascular diseases, BMI body mass index.