Preoperative parathyroid hormone concentration predicts postoperative hypocalcemia severity in dogs undergoing parathyroidectomy.

Preoperative PTH above the upper limit of normal predicts higher risk of severe postoperative hypocalcemia in dogs.

This retrospective study evaluated whether preoperative parathyroid hormone (PTH) concentration could predict moderate to severe postoperative hypocalcemia in dogs undergoing parathyroidectomy for primary hyperparathyroidism. Ninety-two dogs were included, excluding those receiving prophylactic calcitriol. PTH concentrations were stratified by multiples of the assay-specific upper limit of normal (ULN), and postoperative ionized calcium (iCa) nadir was used to classify outcomes, with moderate to severe hypocalcemia defined as iCa < 1.00 mmol/L. Overall, 39.1% of dogs developed moderate to severe hypocalcemia. A clear graded relationship emerged between PTH strata and hypocalcemia severity: 19.1% incidence in dogs with normal PTH, 51.9% with 1–2x ULN, 50.0% with 2–3x ULN, and 100% with >3x ULN. A PTH cutoff of 1.05x ULN yielded an AUC of 0.76 with 72.2% sensitivity and 71.4% specificity. Notably, calcium nadir occurred after 72 hours in 43.5% of all dogs and in 69.4% of those with moderate to severe hypocalcemia, underscoring the need for extended postoperative monitoring. These findings suggest that preoperative PTH stratification is a clinically useful tool for identifying high-risk patients who may benefit from prophylactic calcitriol or calcium supplementation and prolonged monitoring protocols. Clinicians should consider integrating PTH-based risk stratification into perioperative planning for dogs with primary hyperparathyroidism to reduce morbidity associated with postoperative hypocalcemia.

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