title: Parathyroid hormone assays--evolution and revolutions in the care of dialysis patients.
abstract: Renal osteodystrophy may present with low, normal, or high bone turnover. An ideal parathyroid hormone (PTH) assay should discriminate between the bioactive whole PTH-(1-84) molecule and PTH fragments, including the PTH-(7-84) fragment. Most dialysis patients have "intact" PTH (iPTH) levels between 65 and 450 pg/ml, which are poorly predictive of bone turnover state, making the iPTH test of limited value for bone turnover prediction. iPTH levels higher than 500 pg/ml can be observed in some dialysis patients with low bone turnover, while iPTH levels as low as 100 pg/ml have been found in patients with bone turnover above normal, indicating the standard second generation iPTH assay is not a reliable sole indicator of bone turnover. The whole PTH immunoradiometric assay, a third generation assay, uses a detection antibody that recognizes antigenic determinants at the extreme amino-terminal (1-4) end of the PTH molecule, making the assay specific for biologically active whole PTH-(1-84). Comparing results using the whole PTH and iPTH assays, the PTH-(7-84) level is indirectly determined and the PTH-(1-84)/PTH-(7-84) ratio can be calculated. It was shown that PTH-(7-84) inhibits the calcemic effect of PTH-(1-84) and its stimulatory effect on bone turnover. In the interpretation of results using the PTH-(1-84)/PTH-(7-84) ratio, it must be taken into consideration that second generation "intact" PTH assays have different cross-reactivity with PTH-(7-84). Therefore, when comparing or analyzing PTH-(1-84)/PTH-(7-84) ratios, the employed PTH assays must be identical. The whole PTH assay and the PTH-(1-84)/PTH-(7-84) ratio allow more meaningful interpretation of PTH trends, and offer a non-invasive means to more accurately diagnose bone disease in this population.
authors.affiliation: Division of Nephrology, Bone and Mineral Metabolism, Department of Internal Medicine, University of Kentucky, Lexington, KY 40536-0084, USA. hhmall@pop.uky.edu
authors.forename: H H
authors.initials: HH
authors.lastname: Malluche
authors.forename: H
authors.initials: H
authors.lastname: Mawad
authors.forename: D
authors.initials: D
authors.lastname: Trueba
authors.forename: M C
authors.initials: MC
authors.lastname: Monier-Faugere
mesh_terms: D012080:Chronic Kidney Disease-Mineral and Bone Disorder / Q000175:diagnosis*; D006801:Humans; D010281:Parathyroid Hormone / Q000097:blood* / Q000502:physiology; D006435:Renal Dialysis
chemical_list: D010281:Parathyroid Hormone