if you have fever your blood test shows white blood cell get higher then 12.5?

Answer 1

Usually if you have fever, as a sign of infection, your WBC get higher than 10,000. It is because the WBC, when are activated by bacteria or virus, release some substances that produce fever.
Hope this helped you.

Answer 2

If you have anything, infection, arthritis, the white cells will increase. The norm is 7-11% so 12.5 is not that high. Mine tick over at 18% due to the Arthritis and have hit 25% at times. However they can also go high if the blood test was taken after exercise.