The ionic composition of interstitial and intravascular fluids is the same. Proteins, however, are kept with the vascular compartment, at least to a degree, by the vascular wall, which is a semi-permeable membrane. The concentration of proteins is much higher in the plasma sector than in the interstitial sector.
Detection of marijuana using swab drug test can vary from person to person taking into account the different conditions like general health, different fluid intake, metabolism, etc.
Urine testing is able to detect marijuana usage more effectively than a blood test beyond a week. If you suspect someone is abusing marijuana it may be best to use an alternative drug testing method, such as urine testing or hair follicle testing. How Long Does Marijuana Stay in Hair? Hair follicle testing is often considered one of the most accurate methods of drug testing.