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: RESULTS : The 3 patients had acute renal insufficiency , relative metabolic alkalosis , and low parathyroid hormone ( PTH ) , PTH - related peptide , and 1 , 25 - dihydroxyvitamin D concentrations .
### Output Text:
RESULTS : The 3 patients had acute renal insufficiency , relative metabolic alkalosis , and low parathyroid hormone ( PTH ) , PTH - related peptide , and <span class="chemical">1 , 25 - dihydroxyvitamin D</span> concentrations . 