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: Serum creatinine values did not change significantly : 1 . 98 + / - 0 . 8 mg / dL before SRL therapy and 2 . 53 + / - 1 . 9 mg / dL at last follow - up ( P = . 14 ) .
### Output Text:
Serum <span class="chemical">creatinine</span> values did not change significantly : 1 . 98 + / - 0 . 8 mg / dL before <span class="chemical">SRL</span> therapy and 2 . 53 + / - 1 . 9 mg / dL at last follow - up ( P = . 14 ) . 