Biochemist here. I've done genomics, I've done proteomics, I have customers in diagnostic medicine currently. My PhD was on protein-protein interactions, which is a big part of how our immune system works.
A lot of people are quick to jump on the fact that the Theranos system didn't work, and many others claim that it was impossible and never could have worked. While indeed their system didn't work, that doesn't at all disqualify the principle.
For one case study of how far we've come in recent times I point to genomics. The first draft of the human genome took more than a decade start to finish and cost over $1B. Now we can sequence full human genomes on a commercial scale for $500 or less, and it's done in less than a week with far better resolution than the first draft.
From genomics we went to proteomics; classifying proteins in a organism instead of just genes. This tells us more about what cells are doing (although transcriptomics can bridge the gap to a certain extent). Proteins are often better disease markers than genes as well for a similar reason. When proteomics started getting off the ground we were cataloging proteins from large amounts of cellular extract. Now we can catalog and in some cases quantify proteins from individual cells. We can also use protein staining and imaging mass spec to show which cells from a biopsy are expressing aberrant proteins (again as disease markers); we've reached a point where we can do this in real time on live tissue.
One of the biggest faults in the Theranos system was in the fact that blood is not the best serum for disease markers. Yes there are markers in there but not everything goes in there, and not always in quantities that are easy to observe. Blood is great because of how much is in there but lots is missed there as well.