Elevated WBCs s/p PRBC transfusion in sickle cell pt

Got a sickle cell patient the morning after a transfusion of 1 unit PRBCs. CBC showed WBCs of 18, up from a normal count. Reported to MD after reviewing labs along with the improved HGB and a continued K+ elevation of 5.5. We treated the elevated K+, and I asked the doc why the WBCs were elevated. She didn't know. Heme/onc was on consult, but didn't get a chance to ask him. No notes addressing the white count. Tried to google, but didn't find anything. Any ideas?
I found this on Google: Transfusion-related leukocytosis in critically... [Crit Care Med. 2004] - PubMed - NCBI

Awesome! Thank you! My search terms included "sickle cell" which may have filtered out this. Apparently, it may be an idiopathic, transient increase.

The elevated WBC count is non-specific. What did the differential show?