Development of a PTHrP chemiluminescent immunoassay to assess humoral hypercalcemia of malignancy.

BACKGROUND

Parathyroid hormone related peptide (PTHrP) measurements are helpful in the evaluation and management of individuals suspected of humoral hypercalcemia of malignancy (HHM).

AIM: To develop a chemiluminescent assay for PTHrP quantitation, establish reference intervals, and evaluate its clinical performance.

METHOD: PTHrP 1-86 was measured using a polyclonal rabbit antibody (capture) and an acridinium ester labeled goat polyclonal antibody for chemiluminescent detection.

RESULTS

Assay imprecision was < 9% (intra-assay) and < 15% (inter-assay). The analytical measuring range was 0.16-50.5 pmol/L. No significant cross-reactivity was observed for PTH (1-84), PTHrP (107-139), and PTHrP (1-36); whereas PTHrP (38-94) showed 8.3% cross-reactivity. Comparison with the pre-existing Mayo assay showed a positive bias: new assay = 2.24 (pre-existing assay)-0.30 and r2 = 0.96. The reference interval was ≤ 0.7 pmol/L, however, a cut-off of ≤ 4.2 pmol/L yielded increased specificity (98%). Comparison of patients with HHM versus those without HHM resulted in an area under the ROC curve of 0.99. A significant inverse relationship between eGFR and PTHrP was observed (r = 0.738). PTHrP concentrations in patients with Chronic Kidney Disease (CKD) were ≤ 4.2 pmol/L.

CONCLUSION

This assay is specific for PTHrP 1-86. A clinical decision limit of 4.2 pmol/L was sensitive and specific for patients with HHM.