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: Every patient was screened for testosterone and 451 were screened for prolactin on the basis of low sexual desire , gynecomastia or testosterone less than 4 ng . / ml .
### Output Text:
Every patient was screened for <span class="chemical">testosterone</span> and 451 were screened for prolactin on the basis of low sexual desire , gynecomastia or <span class="chemical">testosterone</span> less than 4 ng . / ml . 