You should store it in an airtight container ideally where you don't have temperature extremes.  

If the bag has gotten wet or humidity has affected it, it might be lumpy.  Blood meal is primarily a nitrogen fertilizer, and if it gets wet, some of that nitrogen could have been washed away. Similarly, if it has been kept in a very hot environment, it is possible that some of the nitrogen has gone off as a gas.

However, if it has been kept in a cool, dry place—a basement room or garage, perhaps—it’s probably fine. Use it as the label recommends.

If you are concerned, the compost pile is a great place to use it up. In the unlikely case that no nutrients are left, it’s still a great organic matter addition to compost. And if you do want to discard it, give your garbage hauler a call to see where they want you to put it. Different companies and municipalities may have different procedures.