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: The study involved 129 patients with diabetes with serum creatinine concentrations of 1 . 5 to 3 . 5 mg per deciliter who underwent coronary or aortofemoral angiography .
### Output Text:
The study involved 129 patients with diabetes with serum <span class="chemical">creatinine</span> concentrations of 1 . 5 to 3 . 5 mg per deciliter who underwent coronary or aortofemoral angiography . 