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: Severe and clinically evident anemia of Hb < 11 g / dl with clinical symptoms was detected in 6 patients ( 14 . 3 % ) .
### Output Text:
Severe and clinically evident anemia of Hb < 11 g / dl with clinical symptoms was detected in 6 patients ( 14 . 3 % ) . 