Persistent evidence of blood clotting (increased d-dimer levels) in chronic covid patients might be a reliable way to determine the persistent presence/production of the covid spike protein. another way, discussed below, might be dark field microscopy to look for rouleaux formation of the red blood cells (rbcs)..
Sevick e, jain r (1989) viscous resistance to blood flow in solid tumors: effect of hemocrit on intratumor blood viscosity. cancer research 49:3513-3519. pmid: 2731173 shang j, wan y, luo c et al. (2020) cell entry mechanisms of sars-cov-2. proceedings of the national academy of sciences of the united states of america 117:11727-11734. pmid.
Hemocrit percentage of blood composed of red cells: hemoglobin (grams per deciliter) males: 4.7–6.1 million: red blood cell count. a high red blood count is known as polycythemia..