People on dialysis usually have a procedure to provide a suitable site, which is very long term, but it isn't without it's issues, including infections and takes around 10-12 weeks for the prepared site to be usable. Why do you ask?
Why? To test? Then there's Libre or Dexcom, requiring only 1 'injection' every fortnight or so. To inject? There's the I-port or a pump.
Neither of them have access to blood. Why would you want that?
One treatment for myasthenia gravis is Plasmapheresis which can involve a venous port being implanted on a semipermanent basis never liked it my self though as it can be a bit uncomfortable and sort of reminds me of the Dune film..