What is pit count, as applied in blood work. There are a lot of references on google, but none of them actually define it. What is it?

Platelet count. The platelet count is a subcomponent of the whole blood count. Sometimes they abbreviate it as "plt" or "plts". The normal number of platelet cells is 250, 000 to 400, 000. If they are too low, you could have easy bruising or even bleeding. If they are too high, you can get clots. Primary disease of the platelets is quite rare. More often they are transiently elevated or depressed by infection.