Histamine count
Histamine count was the concentration of histamine in one's system.

One of Iresine Syndrome's symptoms was a decreased histamine count. In 2368, Doctor Beverly Crusher noted that William T. Riker and Deanna Troi's histamine counts were normal, suggesting they didn't have Iresine Syndrome. Later, she suggested they might have contracted a new  of the disease that didn't present with a low histamine count. While considering that others might have been misdiagnosed with Iresine Syndrome despite histamine levels being normal, Geordi La Forge speculated that other medical facilities may have stopped at the obvious diagnosis without digging deeper. ()
Medical measurements