The clinical utility of parathyroid hormone-related peptide in the assessment of hypercalcemia.
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.
Fritchie
Karen
K
University of North Carolina School of Medicine, Department of Pathology and Laboratory Medicine, Chapel Hill, NC 27599, United States.
Zedek
Daniel
D
Grenache
David G
DG
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002118:Calcium / Q000097:blood; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D006934:Hypercalcemia / Q000175:diagnosis*; D007223:Infant; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D044162:Parathyroid Hormone-Related Protein / Q000097:blood*; D012680:Sensitivity and Specificity; D055815:Young Adult
C470125:PTH protein, human; D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D002118:Calcium