Post-parathyroidectomy serum phosphate kinetics is peculiar to female hemodialysis patients with a high body mass index

BACKGROUND: Persistent hyperphosphatemia is one of the most important factors in the development of secondary hyperparathyroidism (sHPTH). Recently, we demonstrated that a higher body mass index (BMI) and female gender could predispose to a larger phosphate (P) body burden, thereby influencing the severity of sHPTH. METHODS: This prospective study aimed to verify if these two risk factors, i.e. BMI and female gender, also influenced calcium (Ca) and P kinetics in the immediate post-parathyroidectomy (PTx) period in 42 consecutive adult Caucasian anuric hemodialysis (HD) patients referred for first PTx. Serum Ca and P were measured pre-PTx and on the 5 consecutive post-PTx days; serum immunoreactive parathyroid hormone (iPTH) and alkaline phosphatase (ALP) levels were measured pre-PTx and 3 days post-PTx. RESULTS: Ablation of parathyroid tissue determined a significant reduction in serum iPTH, ALP, Ca and P (p = 0.001). The stratification of the cohort into four groups according to the cut-off value of BMI = 25 kg/m(2) and according to gender showed the following: males and females with BMI >25 kg/m(2) (analyzed both separately and as a subgroup including males and females) had significantly higher pre-PTx serum P levels, when compared with the respective sub-groups with BMI <25 kg/m(2) (p < 0.01); a significantly higher mean area under the concentration curve (AUC) of serum P was observed in the high BMI group (males and females), when compared with the low/normal BMI group (p = 0.03); the serum P kinetics in the 5 post-PTx days did not differ between the two groups of male patients (low/normal BMI males vs. high BMI males), whereas a significantly higher mean serum P AUC was observed in the high BMI female patients, when compared with the low/normal BMI female patients (p = 0.003); finally, the serum P kinetics in the 5 post-PTx days did not differ between the two groups of low/normal male and female patients, whereas a significantly higher mean serum P AUC was observed in the high BMI female patients, when compared with the high BMI male patients (p = 0.006). A linear multiple regression analysis with the serum P AUC of each patient as a dependent variable and BMI, gender, age and dialysis duration as independent variables showed that BMI (p = 0.0001) and female gender (p = 0.001) were independent predictors of the serum P AUC. CONCLUSIONS: High BMI and female gender are associated with peculiar serum P kinetics in the immediate post-PTx period, suggesting the existence of a larger P body burden in high BMI female HD patients. The existence of a larger P pool exclusively based on serum P kinetics prompts the need for further studies to better understand such intriguing aspects of bone pathophysiology in response to parathyroid gland removal in chronically uremic patients.