The clinical utility of parathyroid hormone-related peptide in the assessment of hypercalcemia

BackgroundHypercalcemia 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.MethodsTest 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.ResultsTest 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.ConclusionsPTHrP testing is more appropriately performed after assessment of PTH. If the PTH is not low or low normal, testing for PTHrP is usually uninformative.