Direct measurement includes elemental assays of hair, blood cells, blood plasma, urine, and sweat.
In hair, low zinc usually means overall zinc deficit, often of dietary or digestive disorder origins. We should be on the lookout for this in children with growth or developmental delays or behavioral disorders where zinc deficiency is frequent. Erythrocytes and leukocytes carry considerable zinc, most of it rather tightly bound. In erythrocytes, zinc is bound as part of CuZn-SOD and to the enzyme carbonic anhydrase. The cell membrane also carries zinc and will lose it in cases of mild zinc insufficiency.