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: Laboratory tests showed an elevation of creatine phosphokinase ( 2218 IU / L ) , aspartate aminotransferase ( 134 IU / L ) , alanine aminotransferase ( 78 IU / L ) , and BUN ( 27 . 9 mg / ml ) levels .
### Output Text:
Laboratory tests showed an elevation of <span class="chemical">creatine</span> phosphokinase ( 2218 IU / L ) , <span class="chemical">aspartate</span> aminotransferase ( 134 IU / L ) , <span class="chemical">alanine</span> aminotransferase ( 78 IU / L ) , and BUN ( 27 . 9 mg / ml ) levels . 