MO812: Risk Factors of Long-Term Hypocalcemia After Parathyroidectomy in Dialysis-Dependent Patients
Authors: Kislyy Pavel , Parshina Ekaterina , Zulkarnaev Aleksei , Tolkach Alexey 
Published: May 2022

Abstract

BACKGROUND AND AIMS
Surgical treatment of secondary hyperparathyroidism (SHPT) is often followed by long-term hypocalcemia, also known as a hungry bone syndrome. We aimed to evaluate the prevalence and risk factors of prolonged hypocalcemia after parathyroidectomy (PTx) for SHPT in dialysis-dependent patients.

METHOD
The retrospective study included 1711 analyses for total serum calcium (Ca) obtained from 372 patients who underwent PTx (either subtotal or total PTx with autotransplantation of parathyroid tissue) for SHPT between 2011 and 2019 in a tertiary care centre of endocrine surgery. The median age of the patients was 50 (IQR 40–57) years, and the median dialysis duration was 82 (IQR 48–134) months. Preoperative parathyroid hormone level was 136 pmol/L (IQR 99.4–210.4), total serum Ca was 2.43 mmol/L (IQR 2.26–2.57) and alkaline phosphatase (AP) was 183 IU/L (IQR 129–395). Follow-up period after surgery ranged from 3 months to 6 years. Postoperative hypocalcemia was defined as a total serum Ca level &lt;2.1 mmol/L, severe hypocalcemia—&lt;1.9 mmol/L. To identify possible risk factors, we took total serum Ca level &lt;2.1 mmol/L after 12 months from PTx as the endpoint.

RESULTS
Hypocalcemia was registered at least once in 81.5% (n = 303), severe hypocalcemiain 59.1% (n = 224) of the patients in the postoperative period. The prevalence of hypocalcemia and severe hypocalcemia gradually decreased from 3 to 24 months post-PTx and remained relatively stable thereafter (Figure 1). The fraction of patients with moderate hypocalcemia (total serum Ca 1.9–2.1 mmol/L) varied from 17% to 41% during 3–60 months of follow-up.
Twelve months after surgery, 53.2% (150 of 282) of the patients had a total Ca level &lt;2.1 mmol/L. Univariate analysis showed no association of hypocalcemia with age (P = .997), sex (P = .17), dialysis vintage (P = .32), modality of treatment (HD/PD, P = .74), type of surgery (P = .29) or use of calcimimetics before surgery (P = .89). Pre-operative parathyroid hormone (P = .55), total Ca (P = .089) and β-crosslaps (P = .69) levels were not associated with an increased risk of hypocalcemia as well. However, low preoperative (P = .037) and postoperative (P = .0092) ionized Ca and high preoperative AP (P = 0.014) levels were associated with an increased risk of long-term postoperative hypocalcemia. Multivariate analysis discovered postoperative ionized Ca as the only independent predictor of prolonged postoperative hypocalcemia [OR = 0.022 (95% confidence interval 0.001–0.356); P = 0.007].

CONCLUSION
We identified a high prevalence of moderate and severe hypocalcemia in the long-term period after PTx in dialysis-dependent patients. Total serum Ca levels return to a normal range at 24 months post-PTx in approximately half of the patients. Patients with low preoperative and postoperative serum ionized Ca and high preoperative AP levels are more likely to have persistent hungry bone syndrome after PTx. Immediate postoperative ionized calcium level is the only independent predictor of long-term hypocalcemia after PTx for SHPT.