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: METHODS : We report the clinical and laboratory data in 3 patients who presented with severe hypercalcemia ( corrected serum calcium > or = 14 mg / dL ) and review the pertinent literature on milk - alkali syndrome .
### Output Text:
METHODS : We report the clinical and laboratory data in 3 patients who presented with severe hypercalcemia ( corrected serum <span class="chemical">calcium</span> > or = 14 mg / dL ) and review the pertinent literature on milk - alkali syndrome . 