Nephrol Dial Transplant (2004) 19: 892-897
Nephrol Dial Transplant Vol. 19 No. 4 © ERA-EDTA 2004; all rights reserved
Original Article
Intact PTH assay overestimates true 1-84 PTH levels after maxacalcitol therapy in dialysis patients with secondary hyperparathyroidism
1Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences and 2Division of Intensive Care Medicine, Niigata University Medical Hospital, Niigata, Japan and 3Scantibodies Laboratory, Inc., Santee, CA, USA
Correspondence and offprint requests to: Junichiro James Kazama MD, PhD, FJSIM, Division of Intensive Care Medicine, Niigata University Medical Hospital, 1-754 Asahimachi-Dori, Niigata, Niigata 951-8510, Japan. Email: jjkaz{at}med.niigata-u.ac.jp
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 µg.
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.
Keywords: estimation; intact parathyroid hormone assay; maxacalcitol; 1-84 parathyroid hormone; secondary hyperparathyroidism
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