Which statement best differentiates iCAL from TCAL?

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Multiple Choice

Which statement best differentiates iCAL from TCAL?

Ionized calcium (iCAL) is the physiologically active pool and is regulated by hormonal control (PTH) while being sensitive to changes in blood pH because binding to albumin shifts with pH. When the pH becomes more alkaline, calcium binds more to albumin, reducing the free ionized fraction; when pH drops (acidosis), more calcium remains ionized. Parathyroid hormone acts to increase the ionized calcium level, affecting this active pool. Total calcium (TCAL), on the other hand, includes both the ionized portion and the calcium bound to proteins, mainly albumin. Its level follows albumin concentration and is largely unaffected by pH changes, since the bound portion tracks albumin rather than the pH-driven shift of the free fraction. So the best differentiator is that iCAL is influenced by PTH and varies inversely with pH, while TCAL is tied to albumin and stays relatively constant with pH.

Ionized calcium (iCAL) is the physiologically active pool and is regulated by hormonal control (PTH) while being sensitive to changes in blood pH because binding to albumin shifts with pH. When the pH becomes more alkaline, calcium binds more to albumin, reducing the free ionized fraction; when pH drops (acidosis), more calcium remains ionized. Parathyroid hormone acts to increase the ionized calcium level, affecting this active pool.

Total calcium (TCAL), on the other hand, includes both the ionized portion and the calcium bound to proteins, mainly albumin. Its level follows albumin concentration and is largely unaffected by pH changes, since the bound portion tracks albumin rather than the pH-driven shift of the free fraction.

So the best differentiator is that iCAL is influenced by PTH and varies inversely with pH, while TCAL is tied to albumin and stays relatively constant with pH.

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