In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Outcomes included CK - MB MI ( CK - MB > or = 8 ng / mL with a relative index [ ( CK - MB x 100 ) / total CK ] > or = 4 , cardiac death , and significant coronary disease ( > or = 50 % ) .
### Output Text:
Outcomes included CK - MB MI ( CK - MB > or = 8 ng / mL with a relative index [ ( CK - MB x 100 ) / total CK ] > or = 4 , cardiac death , and significant coronary disease ( > or = 50 % ) . 