title: Clinical implications of estimation of intact parathyroid hormone (PTH) versus total immunoreactive PTH in normal subjects and hyperparathyroid patients.
abstract: We describe a clinical study comparing the value of measurements of intact human PTH [hPTH(1-84)] and total PTH immunoreactivity [hPTH-(1-84) plus fragments]. A two-step immunochemical method was used to separate plasma hPTH-(1-84) from all circulating PTH fragments. The first step involved extraction and concentration of plasma PTH using solid phase antiamino-terminal PTH antibodies. After elution, the PTH immunoextract was analyzed using a sensitive mid- and C-region immunoassay. Complete separation in the immunoextraction step was proven by Sephadex G-75 gel filtration. hPTH-(1-84) values in fasting patients showed a clear distinction between those with primary hyperparathyroidism and those with nonparathyroid hypercalcemia, in contrast with small overlap in total immunoreactive PTH values. The hPTH-(1-84) values increased faster and more substantially in response to long EDTA and calcium infusion tests, compared with total PTH immunoreactivity, in normal subjects. Infusion of EDTA (10 mg/kg BW) in 5 min) elicited a readily measurable response of hPTH-(1-84) between 5 and 10 min after starting the infusion. Ingestion of 1000 mg calcium caused a decrease in hPTH-(1-84) in 1 h or less. More than 50% of patients with terminal renal failure had normal hPTH-(1-84) values despite elevated total immunoreactive PTH concentrations. We conclude that the two-step hPTH-(1-84) assay is more specific and sensitive than most regional PTH assays. Measurements of hPTH-(1-84) levels may identify disorders of parathyroid function at an early stage and provide a useful tool for the study of parathyroid physiology.
mesh_terms: D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000368:Aged; D002118:Calcium / Q000008:administration & dosage; D004492:Edetic Acid; D006801:Humans; D006961:Hyperparathyroidism / Q000097:blood*; D007120:Immunochemistry; D007263:Infusions, Parenteral; D007676:Kidney Failure, Chronic / Q000097:blood; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D010446:Peptide Fragments / Q000097:blood*; D011863:Radioimmunoassay
chemical_list: D010281:Parathyroid Hormone; D010446:Peptide Fragments; D004492:Edetic Acid; D002118:Calcium