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: METHODS : Urinary pH , albumin , creatinine , the presence of erythrocytes , leukocytes , bacteria and crystals , and culture were analyzed every 3 months for 96 weeks .
### Output Text:
METHODS : Urinary pH , albumin , <span class="chemical">creatinine</span> , the presence of erythrocytes , leukocytes , bacteria and crystals , and culture were analyzed every 3 months for 96 weeks . 