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: Univariate analysis showed that the risk factors associated with seizures after pediatric LT included gender , pediatric end - stage liver disease score before surgery , Child - Pugh score before surgery , serum total bilirubin after surgery , and trough TAC level .
### Output Text:
Univariate analysis showed that the risk factors associated with seizures after pediatric LT included gender , pediatric end - stage liver disease score before surgery , Child - Pugh score before surgery , serum total <span class="chemical">bilirubin</span> after surgery , and trough <span class="chemical">TAC</span> level . 