The amount of a all-trans-retinol dehydrogenase [NAD(+)] ADH7 when measured in blood serum. The trait is level of all-trans-retinol dehydrogenase [NAD(+)] ADH7 in blood serum (OBA_2040519, an Ontology of Biological Attributes entry). Also known as: blood serum all-trans-retinol dehydrogenase [NAD(+)] ADH7 amount.