Haven’t done this myself, however I have worked with protein particles, which is somewhat related. The issue in proteins is trying to keep the protein particles from sticking to each other Unnaturally. This can be done in two ways: 1. I can mix the protein particles with other things. In example: Cooked- out starch is a good tool. The two particles ( protein and starch are easily distinguished, both as is and with iodine stain). The starch acts to interfere with protein agglomeration ( a little like an oil emulsion in food). This allows me to study individual protein particles without having them adhering to each other, or to the starch. In analysis, I simply ignore the starch. Your blood cels and preexisting clots would be responding a little like the protein in this case. You would need to work out a good dilution rate.

2. The other method is to use simple dilution either with water or with a buffer solution.

I believe these methods should work for blood cells, and preexisting blood clots. The blood cells and preexisting clots should be easily distinguish using either method.

Thank you for your answer Var St. Jeor , I will take it into consideration