Since estrogens influence total B12 (but not HoloTC) levels via decreased haptocorrin expression (and thus total decreased B12 concentrations), menopause and HRT could introduce a bias that diminishes the diagnostic accuracies of total B12 in women by reducing the sensitivity for detection of vitamin B12 deficiency at a given cutoff [34, 36, 50–52]. The gene discussed is TCN1; the disease is vitamin B12 deficiency.