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: Current " diagnostic " tests , which primarily include functional and antigenic assays , have more of a confirmatory than diagnostic role in the management of HIT .
### Output Text:
Current " diagnostic " tests , which primarily include functional and antigenic assays , have more of a confirmatory than diagnostic role in the management of HIT . 