What calcium balance was observed in cyclic PN regarding calcium excretion?

• A. A negative calcium balance with an 80% increase in urinary calcium excretion.
• B. A positive calcium balance.
• C. No change in calcium excretion.
• D. An indeterminable balance.

Answer: (D)

In PN, calcium balance is determined by comparing calcium input to all losses, including urine, stool, and any deposition in tissues. In cyclic PN, urinary calcium excretion can fluctuate throughout the infusion cycle due to timing, hydration status, and renal handling, and calcium can be shifted between compartments (bone, intracellular stores) during the cycle. Because you can’t capture the full set of calcium fluxes with a single measurement of excretion, the net balance over the cycle cannot be determined from urine data alone. Therefore the observed calcium balance in cyclic PN is indeterminable without comprehensive intake and all-period loss data.