Bioassay of parathyrin: analytical characteristics and clinical performance in patients with hypercalcemia.
This new bioassay for parathyrin (PTH) in plasma (bio-PTH) combines immunoextraction on affinity columns [goat anti-hPTH (1-44) conjugated to Sepharose 4B] and a receptor assay involving an osteosarcoma cell line. The mean extraction efficacy ranges from 87% (as determined with immunopurified 125I-labeled PTH) to 62% for hPTH bioactivity. The assay is standardized with synthetic hPTH (1-84) and can detect as little as 0.9 pmol/L of PTH in 2 mL of plasma. In 100 healthy adults, the 95% reference interval for bio-PTH was less than 0.9 to 6.1 pmol/L (median, 2.0 pmol/L). In 185 patients with surgically confirmed hyperparathyroidism, bio-PTH concentrations ranged from 1.0 to greater than 120 pmol/L (median, 12.9 pmol/L); 80% of values were greater than 6.1 pmol/L. In 50 patients with both preoperative and postoperative determinations, the mean (+/--SD) concentrations of calcium in serum were 113 +/- 10 and 89 +/- 6 mg/L, respectively; the median bio-PTH concentrations were 13.6 and 2.0 pmol/L, respectively. In 22 patients with nonparathyroid-mediated hypercalcemia, the concentration of bio-PTH ranged from less than 0.9 to 5.3 pmol/L (median, 1.8 pmol/L). This bio-PTH assay is slightly less sensitive than our GP235 immunoreactive PTH (iPTH) immunoassay for detecting hyperparathyroidism (Clin Chem 1982;28:69-74); however, the bioassay is more specific and detected some cases missed by the iPTH assay. Overall, 95% of the hyperparathyroid patients had an increased test result for either the bio-PTH or the iPTH assay.
Klee
G G
GG
Division of Laboratory Medicine, Mayo Clinic, Rochester, MN 55905.
Preissner
C M
CM
Schloegel
I W
IW
Kao
P C
PC
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001681:Biological Assay; D002846:Chromatography, Affinity; D000242:Cyclic AMP / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D006934:Hypercalcemia / Q000097:blood*; D006961:Hyperparathyroidism / Q000097:blood* / Q000601:surgery; D007118:Immunoassay; D008297:Male; D008875:Middle Aged; D012516:Osteosarcoma / Q000378:metabolism; D010281:Parathyroid Hormone / Q000097:blood* / Q000494:pharmacology; D051381:Rats; D014407:Tumor Cells, Cultured
D010281:Parathyroid Hormone; D000242:Cyclic AMP