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: MATERIAL AND METHODS : A total of 33 patients successfully treated with PTRA ( PTRA group , mean age 70 + / - 12 years , 23 female , basal creatinine 1 . 46 + / - 0 . 79 , range 0 . 7 - 4 . 9 mg / dl ) were compared with 33 patients undergoing successful PCI ( PCI group ) , matched for basal creatinine ( 1 . 44 + / - 0 . 6 , range 0 . 7 - 3 . 4 mg / dl ) , gender , and age .
### Output Text:
MATERIAL AND METHODS : A total of 33 patients successfully treated with PTRA ( PTRA group , mean age 70 + / - 12 years , 23 female , basal <span class="chemical">creatinine</span> 1 . 46 + / - 0 . 79 , range 0 . 7 - 4 . 9 mg / dl ) were compared with 33 patients undergoing successful PCI ( PCI group ) , matched for basal <span class="chemical">creatinine</span> ( 1 . 44 + / - 0 . 6 , range 0 . 7 - 3 . 4 mg / dl ) , gender , and age . 