What goes through my head when I get a calcium question...

#1: Is calcium too high or too low?
#2: What is the phospate level?

The question stem might not give calcium levels so I might have to look for the S/S of hyper or hypocalcemia. Hypercalcemia is classically summarized by the mnemonic "stones, bones, abdominal groans and psychic moans". Hypocalcemia is best remembered by the 2 signs associated with it, Chovstek's sign and Trousseau's sign. The tricky part is that hypocalcemia causes tetany, not hypercalcemia. Most people get this backwards.

The phosphate level tells me who is causing the problem, vitamin D or PTH. The "job" of PTH is to increase free calcium and to decrease phosphate. This leads to a high calcium and a low phosphate. The "job" of vitamin D is to increase both calcium and phosphate, increasing bone mineralization.

So if calcium is high and phosphate is low, PTH did its job. If calcium is low and phosphate is high, PTH is sleeping and should be fired.

If both calcium and phosphate are high, vitamin D did its job. If both are low, vitamin D is slacking.

Next post: what to do with your newfound information on PTH and vitamin D activity.