A practical method to predict the severity of hypocalcemia after parathyroidectomy for primary hyperparathyroidism

Presentation: AHNS023
Topic: Quality of Care and Clinical Pathways
Type: Oral
Date: Wednesday, April 18, 2018
Session: 2:20 PM - 3:10 PM Thyroid
Authors: Changxing Liu, MD, PhD, Liyang Tang, MD, Tamara Chambers, MD, Niels Kokot, MD, Uttam Sinha, Dennis Maceri
Institution(s): USC Tina and Rick Caruso Department of Otolaryngology-Head and Neck Surgery, Keck Medicine of USC, University of Southern California

Introduction: Parathyroidectomy is a commonly performed procedure for primary hyperparathyroidism causing either by parathyroid adenoma or hyperplasia. One of the risks for this procedure is postoperative hypocalcemia, which can cause tingling and numbness, tetany, muscular cramps, wheezing, dysphagia, mental status changes, or even seizures and congestive heart failure. Hypocalcemia is the major reason to keep the patients in the hospital. Sometimes, when it’s not recognized initially, and the patients are discharged, they will go to emergency rooms and get readmitted. So, prediction and early intervention of hypocalcemia can decrease hospital cost and prevent severe complications. 

Objective: To predict the severity of hypocalcemia after parathyroidectomy in patients with primary hyperparathyroidism, based on the patients’ clinical information, including patient’s age, length of disease, PTH levels, vitaminD level, and calcium level. To stratify patients into groups with different levels of risk for developing severe hypocalcemia based on these important clinical factors, and to provide guidance for early interventions, including providing oral/iv calcium and vitaminD supplements, to reduce hospital stay and cost.

Methods: Information of 100 patients, diagnosed with primary hyperparathyroidism and underwent parathyroidectomy as the primary treatment modality at USC tertiary care hospital from January 2016 to July 2017, were retrospectively reviewed. Their ages, length of disease, peripheral PTH level before surgery, peripheral PTH level 15minute after abnormal gland(s) removal, vitaminD level, preoperative calcium level, lowest postoperative calcium level, symptoms of hypercalcemia were retrieved and recorded.  R value of Pearson correlation coefficient between the lowest postoperative calcium level with other clinical information, was calculated. p values were calculated based on the correlation coefficient. P<0.05 was set as the threshold for statistical significance.   

Results: Patient’s age, length of disease and vitaminD level provided very minimal information to quantify risks of postoperative hypercalcemia. The absolute difference between the preoperative PTH level and the 15minute PTH level after removal of the abnormal gland(s) in the operating room is the most significant predicting factor for the severity of postoperative hypocalcemia. There is a linear correlation between this absolute difference and the decrease of calcium level postoperatively from preoperative value. A formula was generated to quantify this linear relationship between them as Y=0.0035*X2, while Y= percentage of calcium level drop and X= percentage of PTH level drop, with the value of R>0.7 and p value <0.01. The formula has been tested primarily in our patient population with good reliability.  

Conclusions: Hypocalcemia of post-parathyroidectomy for primary hyperparathyroidism is a transient clinical condition, but it does lead to readmission and long hospital stay, if no adequate, timely prophylactic interventions are provided. Preoperative PTH and intraoperative PTH levels, especially the difference between them can reliably help us calculate the trend of calcium level. Decision of early interventions can be made based on the calculated result from the formula we obtained. As a result, this can decrease the rate of readmission and the length of hospital stay with lower total cost. Our sample is still not large enough, further confirmation with larger samples is desired.