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: Patients who develop ESRD have a higher preoperative and 1 - year serum creatinine and are more likely to have hepatorenal syndrome .
### Output Text:
Patients who develop ESRD have a higher preoperative and 1 - year serum <span class="chemical">creatinine</span> and are more likely to have hepatorenal syndrome . 