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: Persistent sterile leukocyturia was frequently associated with a mild increase in the urine albumin / creatinine ratio and by microscopic hematuria .
### Output Text:
Persistent sterile leukocyturia was frequently associated with a mild increase in the urine albumin / <span class="chemical">creatinine</span> ratio and by microscopic hematuria . 