Blood is made of red blood cells, platelets, plasma etc. Let's say, then, there are these $x$ known compounds in blood. But how can one be sure that there is no other compound other than those $x$ compounds? Does present technology ensure that there is no other unknown compound in blood that can't be detected?

  • $\begingroup$ @user1136 so, there is a probability that we don't know all the elements of blood, yet, right? $\endgroup$
    – Michael
    Mar 24, 2019 at 23:35
  • 2
    $\begingroup$ It all comes down to our ability to detect materials in blood. It would be impossible to rule out the existence of substances below the limit of detection, but would these materials have any significant effect at such low concentrations? $\endgroup$
    – user137
    Mar 25, 2019 at 3:47
  • $\begingroup$ You might be interested in reading about proteomics and metabolomics. Both approaches are capable of untargeted detection and identification of proteins or small molecules, respectively. $\endgroup$
    – Arsak
    Mar 25, 2019 at 17:43


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