Serum calcium is tightly regulated and is only a very small percentage of total body calcium. This is true for other minerals like magnesium and potassium.
True. But again, everyone is different and in my case it did very clearly show - by serum calcium showing clearly and consistently for 2 years below normal range. Thererfore in my case it was that severe that homeostasis couldn't reglate it enough anymore. Definite calcium deficiency.
On the other hand my even more severe Mg-deficiency - confirmed with a whole blood Mg-test - didn't show in serum initially. But gave me the worse symptoms of very painful and severe muscle-cramps. Only overcome with almost monthly Mg-sulfate IVs.
However, with a different perspective of not looking only at 'normal' serum ranges, but optimal ranges, then even in the tightly regulated serum also Magesium deficiency was indicated in my case (sodium and potassium to a lesser extent). For example:
Sodium mmol/l: 136 - 145 normal / 142 -145 optimal range
Cacium 2.2 - 2.55 / ~2,4
Potassium 3.5 - 5.1 / 4 - 5
Magnesium 0.66 - 1.07 / > 0,86
Here the optimal serum Mg comes from a observational study, which found a drastic decrease of overall mortality accosiated with serum levels above 0.86 mmol/.. The others by clinical observations of functional medicine practitioners.
Interesting with Mg-sulfate IVs and the ceasing of Mg-deficiency induced muscle-cramps, serum Mg for the first time in a decade droped even below normal ranges. As if the super-abundance of Mg from IVs had signaled my homeostasis system: there is plenty more coming, and no more need to hold on to it that much anymore.
So by considering also optimal serum ranges, if possible also combined with whole blood tests, symptoms and always possible paradoxical reaction over long periods, also serum values can be very indicative.