Getbig,
Urine tests are very unpredictable actually, but yes, the blood levels are pretty much a direct correlation to whether or not it will show up on the test. It really depends on what steroids your taking. I would suggest you research what steroids to take if your getting tested, as well as the maximum blood levels you can have for them not to show up on the test.
Lawsaver,
Injectible winny has a longer half-life for just that reason: It's injected. I'm not sure as to the specifics, but like any oral-to-injectible comparison (like fina for example), the half-life will be longer when injected.