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: Two weeks after the initiation of therapy , her hematocrit had decreased from 44 . 1 % to 20 . 4 % , and she had a positive direct Coombs antiglobulin test and an elevated indirect bilirubin .
### Output Text:
Two weeks after the initiation of therapy , her hematocrit had decreased from 44 . 1 % to 20 . 4 % , and she had a positive direct Coombs antiglobulin test and an elevated indirect <span class="chemical">bilirubin</span> . 