Varambally et al. found that 43 antidepressant-naive out-patients with depression (assessed using the Mini International Neuropsychiatric Interview) had statistically significantly lower mean serum BDNF level (18.6 ± 4.9 ng/ml) as compared with 24 age-matched healthy controls (23.6 ± 5.6 ng/ml; p < 0.001) [48]. Here, BDNF is linked to depressive symptom measurement.