Yes – this will be better. Chloroquine concentrates in red blood cells and would be a relevant example based on the discussions in the webinar.
In this situation, serum or plasma concentrations are less than the red blood cell concentrations, with haematocrit (Hct) as the adjustment factor. I saw average partitioning as being in a ratio is 1 : 3
However, given that there is between individual variability in Hct – it makes sense to measure the whole blood concentration directly if your lab has the assay.