What is the true measure of hypocalcemia? Low ionized calcium, or low calcium? Thank you.

Depends on context. More information is needed, especially in regards to a correction factor against the serum albumin in hypocalcemia. Ionized calcium is a good measure too, but again, context is necessary. Please see your doctor to help you with clinical context of laboratory values, because the values are not really significant until they are applied to your clinical situation.
Hypocalcemia. Ionized calcium levels give more information about ACTIVE, ionized calcium. If you have abnormal levels of proteins, such as albumin, or immunoglobins in your blood, or have recently had a transfusion of a blood product it may be important to know your ionized calcium levels. If you are otherwise healthy then the total calcium level is what we use to define hypocalcemia.

Related Questions

What's the difference between low ionized calcium and low calcium? Which one is the true measure of hypocalcemia?

Both. If you can measure (rarely done), calculate (complicated formula) or estimate (calcium minus albumin), you will get the ionized calcium. About half of the calcium in the blood is ionized and this is the active form. In real-life, this means that a lot of sick people with low albumin also have low total calcium but needn't worry as the physiologic ionized calcium is what's regulated. Read more...

What triggers the INTACT PTH to become high? Is it the low calcium? Or what triggers having low ionized calcium, is it the high INTACT PTH?

Several reasons. There are several triggers to high PTH, and you will need to see your doc for workup. Some things that can do this are of primary cause (happens on its own i.e. adenoma), low vitamin D levels, somewhat advanced chronic kidney disease, low calcium levels. As always, labs are just labs, but the clinical context is where the importance lies. Please follow up with your doc about this. Read more...