My 9 Year Old Daughter Had A Temperature Between 100.1

My 9 year old daughter had a temperature between 100.1 to 103.1 for 4 nights five days we went to doctor said it was a flu then told her about her tenderness in right shoulder blade. We then had an x-ray done. and now I just received a call from her Doctor a personal call telling me to get her a blood test which I did. What could they be looking for?