Yes, it does seem very high.
3726.04 mIU/mL = 3726.04 IU/L
48.2 IU/L = 48.2 mIU/mL
Greater than 10 IU/L (10 mIU/mL) is considered to be protective.
Convering from IU/L to mIU/ml gives the same result as the number you are converting from. This is because to convert to mIU/ml from IU/L you would have to multiply both the numerator and denominator by 1000, and these numbers cancel each other giving you the same result.
Converting from mIU/ml to IU/L gives also the same result, though in this case you divide both the denominator and numerator by 1000; and they cancel each other as before. So, as Stephen wrote: 48.2 IU/L = 48.2 mIU/ml