This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: nutrition and digestion, Subject name: Biochemistry
[{'content': 'Which of the following is considered the active form of calcium? \nSelect and explain. \nA. Ionised calcium, B. Albumin bound calcium, C. Phosphate bound calcium, D. Protein bound calcium', 'role': 'user'}, {'content': 'Answer: A \nExplanation: In blood viually all of calcium is in the plasma, which has a mean normal calcium concentration of approximately 9.5mg/dl. calcium exists in 3 chemical states in plasma, of which 50% is Ionised , 40% is bound to proteins, 10% is complexed with small anions. The free or ionised calcium is the biologically active form . Its concentration in plasma is tightly regulated by vitamin D and parathyroid hormone. Teitz textbook of clinical biochemistry , 6th edition,section 5, page number 1736.', 'role': 'assistant'}]