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Background: Plasma PTH levels are normally high during the night and early morning and lowest at approximately 10 am (the PTH circadian rhythm). Our objective was to examine the relationship between the PTH circadian rhythm and calcium-phosphorus metabolism in non-dialyzed, chronic kidney disease (CKD) patients.
Methods: The characteristics of twenty-eight subjects comprised: male, 23; diabetic patients, 16; mean age, 71.1 ± 10.5 years; mean eGFR, 18.3 ± 8.1 mL/min/1.73 m2. Under a protein-restricted diet, plasma intact PTH (iPTH) was measured at 7 am (iPTH7), 10 am (iPTH10), and 10 pm (iPTH22). Serum concentrations of calcium (Ca), phosphate (Pi), 25-hydroxyvitamin D (25-OHD), 1,25-dihydroxyvitamin D (1,25[OH]2D), and fibroblast growth factor (FGF)-23 were measured at 7 am. A normal iPTH rhythm was defined as when both iPTH7 and iPTH22 exceeded iPTH10. When iPTH10 was equal to, or exceeded either iPTH7 or iPTH22, or both, the rhythm was considered abnormal.
Results: Median levels of iPTH7, iPTH10, and iPTH22 were 92.5 [IQR: 60.8 - 152.0], 85.5 [61.0 - 144.5], and 95.5 [64.3 - 160.5] pg/mL, respectively. Sixteen subjects showed an abnormal iPTH rhythm. There was no significant difference between groups in age, eGFR, iPTH7, iPTH10, iPTH22, Pi, 25-OHD, 1,25(OH)2D, or FGF-23. However, the abnormal group showed significantly higher mean levels of corrected Ca as compared to the normal group (9.50 ± 0.42 vs. 9.18 ± 0.28; p = 0.032).
Conclusions: Abnormal diurnal patterns of PTH are associated with sustained mild hypercalcemia in nondialyzed chronic kidney disease patients. This abnormal rhythm was not associated with Pi or FGF-23, and this may be an independent risk factor for CKD-mineral and bone disorder.
DOI: 10.7754/Clin.Lab.2015.150531
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