Assuming you're trying to get prescribed TRT? It depends what kind of blood work they are doing, if they are just simply doing a normal blood work panel and not specifically testing for AAS then just shooting a few hundred mg's of deca a few weeks before your apt will DEFINITELY have your test levels low...but deca is going to show up if they are testing for AAS(which they probably aren't). Most likely won't be able to get it up for those few weeks though, and run some clomid after your bloodwork to get the ball rolling again.
Another option, which i've actually used with success is to get some test suspension(TNE), could maybe make it work with prop, run it for a week or so and then cut it 2-3 days before your blood test. Susp clears the system so quickly that you'll only have to deal with the adverse effects for a day or so. Again, will want to run some clomid afterward if you want to get the boys going again, although i doubt you do if you are looking to get prescribed TRT.
*Just want to put a disclaimer out there before someone freaks out, i'm NOT suggesting that you do this, i've done it with success however it is undoubtedly not ideal for your health and will not guarantee you the results you are looking for.