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: The diagnosis of propylthiouracil ( PTU ) - associated vasculitis was made by observation of consistent clinical features , the detection of elevated ANA and ANCA in the blood , and the observed clinical resolution of symptoms following withdrawal of PTU .
### Output Text:
The diagnosis of <span class="chemical">propylthiouracil</span> ( <span class="chemical">PTU</span> ) - associated vasculitis was made by observation of consistent clinical features , the detection of elevated ANA and ANCA in the blood , and the observed clinical resolution of symptoms following withdrawal of <span class="chemical">PTU</span> . 