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: Sensitivities , specificities , and positive and negative likelihood ratios for predicting cardiac death or significant disease were high for both CK - MB MI and cTnI and were not significantly different .
### Output Text:
Sensitivities , specificities , and positive and negative likelihood ratios for predicting cardiac death or significant disease were high for both CK - MB MI and cTnI and were not significantly different . 