Table 2.
Variables | Number of association studies | Subgroup analysis
|
Heterogeneity
|
||||
---|---|---|---|---|---|---|---|
SMD | 95% CI lower | 95% CI upper | p-value | l2 (%) | Q (p-value) | ||
Blood sampling | |||||||
Plasma | 10 | 0.62 | 0.31 | 0.93 | 0.0001 | 75.9 | 2.9×10−4 |
Serum | 2 | 0.16 | −0.12 | 0.45 | 0.26 | 0 | 0.42 |
Glutamate assay | |||||||
HPLC | 8 | 0.41 | 0.22 | 0.60 | <0.0001 | 28.5 | 0.22 |
MS | 4 | 0.69 | −0.069 | 1.45 | 0.075 | 89.7 | <1.0×10−4 |
Medication | |||||||
Medication free | 8 | 0.59 | 0.19 | 1.00 | 0.004 | 72.9 | 6.8×10−4 |
Food consumption | |||||||
Fasting | 4 | 0.33 | 0.063 | 0.59 | 0.015 | 0 | 0.51 |
Not fasting | 3 | 0.90 | 0.031 | 1.77 | 0.042 | 94.1 | <1.0×10−4 |
Ethnicity | |||||||
Asian | 7 | 0.58 | 0.14 | 1.02 | 0.01 | 88.6 | <1.0×10−4 |
Non-Asian | 5 | 0.48 | 0.21 | 0.76 | 0.0006 | 0 | 0.84 |
Abbreviations: MDD, major depressive disorder; SMD, standardized mean difference; HPLC, high-performance liquid chromatography; MS, mass spectroscopy.