I concur with respondent Lacie
, in that the buoyant while substance you saw in the blood sampling tube is likely the result of hyperlipidemia. I'm not so sure about White Thrombus formation however, as that seems to occur more so with specific types of hemodialysis tubing (and is also observed with banked blood)
, in addition to being proportionately dependent upon hematocrit levels (see here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2390940/
Additionally, as PROPOFOL (DIPRIVAN) enters the blood stream, it is dissolved and rapidly absorbed by peripheral tissues. I'm certainly no pharmacist, but IMHO, I honestly question if there is enough remaining within circulating blood to separate out of solution like your description.
Hence, my vote is for excess blood lipids.