This is not to be confused with blood being thick.
Blood being thick has to do more with viscosity that is influenced by rheological factors such as the many components in blood agglomerating. If you want to check blood thickness, you could check your serum ESR.
I have to explain this better:
Pumpkin soup - add water to double the volume. If pumpkin is red blood cell, the undiluted soup would be considered dehydrated vs. the diluted soup. If you measure the pb (pumpkin bits/ml), the undiluted soup would be twice that of the diluted soup. Certainly, undiluted soup would be thicker, but this isn't the 'thick' we're talking about when we talk about blood thickness. We're talking about viscosity, or the resistance to flow.
If you add a starch thickener to the pumpkin soup, to make it have more body by gelling it, the result would be a soup that is "thicker"in the sense that we would call blood "thick." In blood, as well as in industrial colloidal mixtures, a term called zeta potential is used to describe this resistance to flow. Search the zeta potential thread to get a better understanding of this.