Intact PTH assay overestimates true 1-84 PTH levels after maxacalcitol therapy in dialysis patients with secondary hyperparathyroidism.

Abstract

BACKGROUND:

Although the so-called intact parathyroid hormone (iPTH) assay detects not only true 1-84 PTH (1-84PTH) but also large C-terminal PTH fragments, it remains inconclusive whether the 1-84PTH assay is more useful in clinical practice. Previous studies have shown that the results of these two PTH assays in dialysis patients are closely correlated.

METHODS:

Chronic dialysis patients whose plasma iPTH levels were >400 pg/ml were selected for inclusion in the present study. Following a 4 week wash-out time during which all vitamin D administration was halted, maxacalcitol was intravenously injected at the end of dialysis sessions three times per week for 24 weeks, at an initial dosage of 10 micro g.

RESULTS:

Ninety-seven patients with secondary hyperparathyroidism were included in our analysis. Their serum calcium levels were elevated from the start levels while phosphate levels remained unchanged. The plasma 1-84PTH levels constantly declined throughout the 24 weeks. Although the patients' plasma 1-84PTH and iPTH levels were closely correlated with each other both at the beginning of the study and after 24 weeks of maxacalcitol therapy, the ratio of 1-84PTH/iPTH consistently decreased throughout the study period (P<0.01). The changes in the ratio were significantly correlated with changes in serum calcium levels.

CONCLUSIONS:

Twenty-four weeks of intravenous maxacalcitol injection therapy significantly reduced the 1-84PTH/iPTH ratio. Estimated 1-84PTH levels from iPTH levels using a conversion formula obtained before the treatment were 21.0+/-20.4% higher than measured 1-84PTH levels after the therapy. Thus, iPTH measurement has a potential risk to overestimate 1-84PTH levels when evaluating the efficacy of maxacalcitol therapy in dialysis patients with secondary hyperparathyroidism.

• Authors: Junichiro J Kazama, Kentaro Omori, Noboru Higuchi, Naoki Takahashi, Yumi Ito, Hiroki Maruyama, Ichiei Narita, Thomas L Cantor, Ping Gao, Fumitake Gejyo
• Journal: Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association (Nephrol Dial Transplant) Vol. 19 Issue 4 Pg. 892-7 (Apr 2004) ISSN: 0931-0509 [Print] England
• PMID: 15031346 (Publication Type: Journal Article)

Chemical References

• Parathyroid Hormone
• Calcitriol
• maxacalcitol

Topics

• Calcitriol (analogs & derivatives, therapeutic use)
• Female
• Humans
• Hyperthyroidism (blood, drug therapy)
• Male
• Middle Aged
• Parathyroid Hormone (blood)
• Prospective Studies
• Renal Dialysis
• Reproducibility of Results