My AST And My ALT Were Substantially Elevated Compared To

My AST and my ALT were substantially elevated compared to my last blood test just a few months ago. My A1C is 6.0 and I take simivastatin (Zocor) for years. Could you please tell me what would cause a spike in my AST and ALT?
On 5/2015 my AST was 23 but it spiked to 66 on 12/30/2015.
On 5/2015 my ALT was 18 but it spiked to 41 on 12/30/2015.
My hepatitis panel came back all non-reactive.
Could you please tell me what could be the cause in this spike??
Thank you,
Rona Traub