Your Dr is double checking to see if there was some error with the first blood test. There is probably nothing to get overly worried about. A high white cell count may indicate that your body is fighting some form of infection.
Blood Test results are frequenty questionable at this time of year, what with the seasononal colds, the christmas new year period, stress, worries and also the change in what we generally eat.
Let us know what the 2nd Blood Test result shows, it might well that there was nothing to become overly worried about.