Karen Fritchie1, Daniel Zedek, David G Grenache. 1. University of North Carolina School of Medicine, Department of Pathology and Laboratory Medicine, Chapel Hill, NC 27599, United States.
Abstract
BACKGROUND: Hypercalcemia is a common clinical finding with primary hyperparathyroidism and malignancy accounting for most cases. Measurement of parathyroid hormone-related peptide (PTHrP) is often requested for patients with hypercalcemia before confirmation of hypercalcemia and/or determination of parathyroid hormone (PTH) concentrations. We determined a PTH cutoff to guide PTHrP testing in hypercalcemic patients. METHODS: Test results for total calcium, intact PTH, and PTHrP tests performed within 2 days of each other were recorded. Chart review determined the etiology of hypercalcemia. The PTH cutoff below which a PTHrP result might be useful was determined. RESULTS: Test results from 123 patients were included and 47 had hypercalcemia of malignancy, 15 of which had increased PTHrP. Diagnostic sensitivity and specificity were 32% (95% CI=19-47%) and 95% (95% CI=85-99%), respectively. PTH concentrations were lowest in patients with increased PTHrP compared to those with no increase (25.6+/-69.2 vs. 94.8+/-332.8 ng/l, p<0.01). A cutoff PTH concentration of >26 ng/l predicted a non-increased PTHrp result in 95% of the entire study population which increased to 100% when only patients with hypercalcemia were considered. CONCLUSIONS: PTHrP testing is more appropriately performed after assessment of PTH. If the PTH is not low or low normal, testing for PTHrP is usually uninformative.
BACKGROUND:Hypercalcemia is a common clinical finding with primary hyperparathyroidism and malignancy accounting for most cases. Measurement of parathyroid hormone-related peptide (PTHrP) is often requested for patients with hypercalcemia before confirmation of hypercalcemia and/or determination of parathyroid hormone (PTH) concentrations. We determined a PTH cutoff to guide PTHrP testing in hypercalcemic patients. METHODS: Test results for total calcium, intact PTH, and PTHrP tests performed within 2 days of each other were recorded. Chart review determined the etiology of hypercalcemia. The PTH cutoff below which a PTHrP result might be useful was determined. RESULTS: Test results from 123 patients were included and 47 had hypercalcemia of malignancy, 15 of which had increased PTHrP. Diagnostic sensitivity and specificity were 32% (95% CI=19-47%) and 95% (95% CI=85-99%), respectively. PTH concentrations were lowest in patients with increased PTHrP compared to those with no increase (25.6+/-69.2 vs. 94.8+/-332.8 ng/l, p<0.01). A cutoff PTH concentration of >26 ng/l predicted a non-increased PTHrp result in 95% of the entire study population which increased to 100% when only patients with hypercalcemia were considered. CONCLUSIONS:PTHrP testing is more appropriately performed after assessment of PTH. If the PTH is not low or low normal, testing for PTHrP is usually uninformative.