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: Changes in serum creatinine after intervention ( after - before ) were significantly different between the PTRA and PCI groups ( - 0 . 12 + / - 0 . 5 vs . 0 . 13 + / - 0 . 3 , P = 0 . 014 ) .
### Output Text:
Changes in serum <span class="chemical">creatinine</span> after intervention ( after - before ) were significantly different between the PTRA and PCI groups ( - 0 . 12 + / - 0 . 5 vs . 0 . 13 + / - 0 . 3 , P = 0 . 014 ) . 