This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Modes of Ventilation, Subject name: Anaesthesia
Which is biomarker of in ventilation associated pneumonia 
Select and explain. 
A. Procalcitonin, B. C - reactive protein, C. ESR, D. CA19-9
A: Procalcitonin
Answer: A: Procalcitonin 
Explanation: Procalcitonin (PCT) is a precursor of calcitonin that is constitutively secreted by C cells of the thyroid gland and K - cells of the lung. In healthy individuals PCT is undetectable when stimulated by endotoxin PCT is rapidly produced.