Final answer:
Total blood calcium includes ionized calcium, protein-bound calcium, and calcium complexed with other substances; ionized calcium is the biologically active component critical for various physiological functions. Normal blood values for total calcium are 9.5-10.5 mg/100 ml, with about 55-65% existing as ionized calcium.
Step-by-step explanation:
The difference between total blood calcium and ionized calcium largely concerns their physiological roles and states in the blood. Total blood calcium includes all the calcium present in the blood, which is a sum of ionized calcium, protein-bound calcium, and calcium complexed with other substances like organic acids, phosphate, and citrate. Ionized calcium refers to the fraction of calcium that is freely floating in the blood plasma and is biologically active, playing critical roles in muscle contraction, enzyme activity, blood coagulation, cell membrane stability, neurotransmitter release, and hormone secretion. Normal blood values for total calcium range between 9.5-10.5 mg/100 ml, with about 55-65% of this in ionized form. Whereas changes in ionized calcium levels can have immediate physiological implications, such as causing tetany when levels drop too low.