Ariadne,
This is "normal" post a splenectomy - this is due to:
1. The spleen acts as a filter and removes the deformed, dying and dead cells (RBCs/WBCs) from the body - in the absence of a spleen, these cells get to "circulate" around the body longer, before they just "dissolve". As a result, you will always get a high WBC count. Your platelet counts should also be high or at the high end of the range.
2. Machine tests read the blood counts improperly - typically, when your blood is analysed by the machine, it uses a math program to distinguish between the cells, which is determined by size of the cells among others - I don't know if your lab in the US will do this, but ask them for a "Hand Count" to correct for the absence of the spleen. The way this is done is by smearing a blood drop on a slide, and manually counting under an electron microscope. I have had this "hand count" correction done a few times, just to check when my counts spiked. I count 20-25K as "normal" for me!
If the hand count still shows a high count, or if a hand count is not possible, you would need to get a few tests done for chronic infections. That could be the other cause.
Cheers
Poirot