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

OBJECTIVE

To evaluate preoperative parathyroid hormone (PTH) concentration as a predictor of moderate to severe postoperative hypocalcemia following parathyroidectomy in dogs with primary hyperparathyroidism.

METHODS

Retrospective analysis of dogs undergoing parathyroidectomy for primary hyperparathyroidism and excluding dogs receiving prophylactic calcitriol. Preoperative serum PTH measurement was stratified into groups by multiples of the assay-specific upper limit of normal (ULN). Whole blood ionized calcium (iCa) nadir was used to classify postoperative outcome, with moderate to severe hypocalcemia defined as iCa < 1.00 mmol/L.

RESULTS

92 dogs were included. Moderate to severe hypocalcemia occurred in 36 dogs (39.1%). A graded relationship was identified between PTH strata and moderate to severe hypocalcemia: 9 of 47 dogs (19.1%) with normal PTH, 14 of 27 (51.9%) with > 1 to 2 times ULN, 5 of 10 (50.0%) with > 2 to 3 times ULN, and 8 of 8 (100%) with > 3 times ULN. A PTH cutoff of 1.05 times ULN yielded an area under the curve of 0.76 (95% CI, 0.65 to 0.86), with 72.2% sensitivity and 71.4% specificity. Median time to overall calcium nadir was 65.8 hours (range, 3.7 to 19,794.1), with 40 of 92 dogs (43.5%) reaching nadir after 72 hours. Late nadirs were common in dogs with moderate to severe hypocalcemia (25 of 36 [69.4%]) versus normocalcemia (10 of 44 [22.7%]).

CONCLUSIONS

Preoperative PTH concentration stratified by ULN multiples demonstrates a graded relationship with postoperative hypocalcemia.

CLINICAL RELEVANCE: PTH-based stratification could identify high-risk patients warranting prophylactic therapeutics and extended monitoring.