Abstract
Purpose
The purpose of this study is to evaluate a percent change model of postoperative parathyroid hormone level in thyroidectomy patients as a predictor of hypocalcemia.
Materials and methods
Chart review was completed on patients who had undergone total or completion thyroidectomy over a 22-month period in our department. Only those patients with a preoperative ionized calcium and parathyroid hormone (PTH) level and at least 1 postoperative result were included. Ionized calcium levels served as an internal control. The Student t test was used to compare PTH level between the normocalcemic and hypocalcemic groups at each time point. Logistic regression analysis was used to predict hypocalcemia based on the diagnostic criteria. Receiver operator curves were used to maximize sensitivity.
Results
Fifty-two patients met the inclusion criteria during the study period. A total of 22 patients (42%) experienced hypocalcemia. We were unable to maximize both sensitivity and specificity at the same time point. When comparing preoperative to 6-hour postoperative PTH percent change, patients with a greater than 44% decrease are likely to have hypocalcemia, with a sensitivity of 100%. Likewise, in those patients without a greater than 44% decrease at 6 hours, early discharge can be considered safe, given the negative predictive value of 100%.
Conclusion
In our series, patients with a greater than 44% PTH decrease from preoperative to 6-hour postoperative are very likely to develop hypocalcemia. We would propose that these patients need further inpatient monitoring to progress to safe discharge. Likewise, patients with a less than 44% decrease at the 6-hour time point are unlikely to develop hypocalcemia and may be considered safe for discharge.
1
Introduction
Hypocalcemia is the most common etiology for prolonged hospitalization in patients undergoing total thyroidectomy . Traditional methods for detecting hypocalcemia in the postoperative period include frequent monitoring of total and ionized calcium (ICa) levels as well as close clinical monitoring for symptoms of hypocalcemia. These traditional methods can take 24 hours or longer to reveal hypocalcemia, which can prolong hospitalization. A clinical laboratory method for early prediction of postoperative hypocalcemia could, therefore, facilitate earlier discharge (≤24 hours) and improve outcomes after total thyroidectomy.
The risks of postoperative hematoma and airway compromise are highest during the first 24 hours after thyroidectomy. However, symptomatic hypocalcemia may not manifest itself during the first 24 hours . With the advent of pay-for-performance measures, many endocrine surgeons are interested in early predication of hypocalcemia, both to prevent serious complications and to begin early treatment in an effort to hasten hospital discharge.
Over the past 20 years, clinical research has focused on determining an efficient method for monitoring and predicting postoperative hypocalcemia. Initial efforts focused on early perioperative serum calcium slopes; however, these ultimately proved to have limited negative predictive values (NPVs) . In recent years, multiple retrospective studies have emerged, which support the use of postoperative serum parathyroid hormone (PTH) levels as accurate predictors of hypocalcemia in postoperative thyroidectomy patients.
A recent meta-analysis examined the pooled data from 9 individual studies examining postoperative PTH levels as predictors of hypocalcemia. This demonstrated that PTH levels at 6 hours postoperatively had a sensitivity of 96.4% and a specificity of 91.4% for detecting postoperative hypocalcemia . Several studies have attempted to correlate PTH levels with clinical outcome while still using calcium levels and clinical picture as the criterion standard. Vescan et al performed a prospective study of 201 patients undergoing total thyroidectomy. Postoperative PTH levels were assessed 1 hour after the procedure and also the following morning. Standard calcium levels and symptom monitoring were used to determine disposition. Results suggested that patients with PTH levels greater than 1.6 pmol/L at 1 hour were likely to remain normocalcemic. Patients with PTH levels less than 1.1 pmol/L at 1 hour were more at risk for developing hypocalcemia.
Scurry et al also evaluated postoperative PTH levels in thyroidectomy patients. They determined that accurate predictors for the development of symptomatic hypocalcemia included a decrease in PTH by 75% as well as an absolute postoperative PTH of 7 pg/mL. Payne et al have published considerable research on this topic as well. In several articles, they have demonstrated that a PTH greater than 28 ng/L (pg/mL) combined with a normal calcium level at 6 hours postthyroidectomy can be predictive of patients that will maintain normocalcemia. They accomplished a specificity of 100%, sensitivity of 67.9%, and 100% positive predictive value.
Based on the aforementioned studies, we have been using patient PTH levels in the perioperative period to assist in decision making and discharge planning since January 2008. However, because of differing reports and variable conclusions in the literature, we have only been able to use these data as an adjunct to clinical decision making while still relying on the criterion standard of ICa levels to predict postoperative hypocalcemia.
We have observed that most reports suggest using an absolute cutoff value as a predictor of potential hypocalcemia. We find this approach to be problematic due to the wide range of reporting units (picomolar, picogram per milliliter, and nanogram per liter) and the existence of inherent variability between the assay type/methodology and logistics at different clinical laboratories. Preoperative PTH levels might also be an important consideration, especially in patients with abnormal preoperative parathyroid function. As such, the overarching goal of our study was to examine the use of a percent change model for serum PTH level to predict postoperative hypocalcemia after thyroidectomy.
2
Materials and methods
2.1
Study design
After obtaining institutional review board approval, we retrospectively reviewed hospital and clinic records of patients who had undergone total or completion thyroidectomy in our department from January 1, 2008, to October 30, 2009. Primary surgeons included the 3 senior authors (JDB, CAS, and JDW). Ionized calcium levels were used for the internal control group. Intact PTH levels (PTH) were obtained using a standard commercial immunoassay, which measures 1.84 intact PTH molecule (institutional reference range, 12–72 pg/mL). Parathyroid hormone levels were evaluated at the following time points: preoperatively (any time from 30 days before the procedure to immediately before incision), immediately postoperative (exactly 10 minutes after passing off the surgical specimen), and 6 hours postoperatively. Ionized calcium levels were obtained at the following time points: preoperatively; immediately postoperative; and then 6, 12, 24, 36, and 48 hours postoperatively, followed by daily levels for the remainder of hospitalization. These values were rarely obtained after the 24-hour time point, unless the patient remained in the hospital secondary to high drain output, unresponsive or worsening hypocalcemia, or other medical comorbidities. Patients experiencing symptoms of hypocalcemia or with ICa less than 1.00 mmol/L (institutional reference range, 1.00–1.30 mmol/L) were started on oral calcium supplementation and calcitriol immediately. Patients with significant hypocalcemia (ICa <0.80 mmol/L, severe symptoms, or known cardiac conduction problems) were treated with intravenous calcium gluconate, in addition to initiation of oral calcium supplementation and calcitriol.
2.2
Inclusion criteria
To be included, the patient required both preoperative and at least 1 set of postoperative PTH and ICa levels. Data reviewed included patient age, sex, date of surgery, primary surgeon, procedure performed, pathologic diagnosis, laboratory values (ICa and PTH), and symptoms.
2.3
Exclusion criteria
Patients were excluded from the study if they were undergoing an extended procedure such as total laryngectomy or parathyroidectomy. They were also excluded if they were taking preoperative osteoporotic medications or prophylactic vitamin D and calcium supplementation. Patients with preexisting chronic renal disease, hyperparathyroidism, or known digestive disease were also excluded.
2.4
Outcome measures
Our primary outcome measure was the development of hypocalcemia, as predicted by percent change in PTH level. Hypocalcemia was defined as either a fall in the patient’s ICa level below 1.00 mmol/L or signs/symptoms of hypocalcemia during the postoperative period (up to 14 days postoperatively). Commonly accepted signs of hypocalcemia include the Chvostek sign, Trousseau sign, and cardiac arrhythmias. Common symptoms of hypocalcemia that were assessed include perioral paresthesias, distal digital paresthesias, tetany, and palpitations (as documented in the patient’s daily progress notes or postoperative clinic notes).
2.5
Statistical analysis
Patient demographics and basic characteristics were presented as mean/SD for continuous variables such as age. Patient demographics and basic characteristics were presented as percentages for categorical variables such as sex, procedure, pathologic diagnosis, signs/symptoms of hypocalcemia, and hypocalcemia proven by laboratory values. Mean PTH levels were calculated at each time point (preoperatively, immediately postoperatively, and 6-hour postoperatively), and the 2-sided Student t test was performed to compare the normocalcemic and hypocalcemic groups. Logistic regression was used to predict hypocalcemia based on the diagnostic criteria. Sensitivity and specificity were then calculated based on different cutoff points from the logistic regression model. Receiver operator curves were plotted with sensitivity vs 1-specificity. The cutoff point with maximum sensitivity was chosen as optimal for this screening test. Diagnosis criteria included both absolute PTH change and percent change for the immediate postoperative time point and the 6-hours postoperative time point. Sex effect was also examined using logistic regression model.
2
Materials and methods
2.1
Study design
After obtaining institutional review board approval, we retrospectively reviewed hospital and clinic records of patients who had undergone total or completion thyroidectomy in our department from January 1, 2008, to October 30, 2009. Primary surgeons included the 3 senior authors (JDB, CAS, and JDW). Ionized calcium levels were used for the internal control group. Intact PTH levels (PTH) were obtained using a standard commercial immunoassay, which measures 1.84 intact PTH molecule (institutional reference range, 12–72 pg/mL). Parathyroid hormone levels were evaluated at the following time points: preoperatively (any time from 30 days before the procedure to immediately before incision), immediately postoperative (exactly 10 minutes after passing off the surgical specimen), and 6 hours postoperatively. Ionized calcium levels were obtained at the following time points: preoperatively; immediately postoperative; and then 6, 12, 24, 36, and 48 hours postoperatively, followed by daily levels for the remainder of hospitalization. These values were rarely obtained after the 24-hour time point, unless the patient remained in the hospital secondary to high drain output, unresponsive or worsening hypocalcemia, or other medical comorbidities. Patients experiencing symptoms of hypocalcemia or with ICa less than 1.00 mmol/L (institutional reference range, 1.00–1.30 mmol/L) were started on oral calcium supplementation and calcitriol immediately. Patients with significant hypocalcemia (ICa <0.80 mmol/L, severe symptoms, or known cardiac conduction problems) were treated with intravenous calcium gluconate, in addition to initiation of oral calcium supplementation and calcitriol.
2.2
Inclusion criteria
To be included, the patient required both preoperative and at least 1 set of postoperative PTH and ICa levels. Data reviewed included patient age, sex, date of surgery, primary surgeon, procedure performed, pathologic diagnosis, laboratory values (ICa and PTH), and symptoms.
2.3
Exclusion criteria
Patients were excluded from the study if they were undergoing an extended procedure such as total laryngectomy or parathyroidectomy. They were also excluded if they were taking preoperative osteoporotic medications or prophylactic vitamin D and calcium supplementation. Patients with preexisting chronic renal disease, hyperparathyroidism, or known digestive disease were also excluded.
2.4
Outcome measures
Our primary outcome measure was the development of hypocalcemia, as predicted by percent change in PTH level. Hypocalcemia was defined as either a fall in the patient’s ICa level below 1.00 mmol/L or signs/symptoms of hypocalcemia during the postoperative period (up to 14 days postoperatively). Commonly accepted signs of hypocalcemia include the Chvostek sign, Trousseau sign, and cardiac arrhythmias. Common symptoms of hypocalcemia that were assessed include perioral paresthesias, distal digital paresthesias, tetany, and palpitations (as documented in the patient’s daily progress notes or postoperative clinic notes).
2.5
Statistical analysis
Patient demographics and basic characteristics were presented as mean/SD for continuous variables such as age. Patient demographics and basic characteristics were presented as percentages for categorical variables such as sex, procedure, pathologic diagnosis, signs/symptoms of hypocalcemia, and hypocalcemia proven by laboratory values. Mean PTH levels were calculated at each time point (preoperatively, immediately postoperatively, and 6-hour postoperatively), and the 2-sided Student t test was performed to compare the normocalcemic and hypocalcemic groups. Logistic regression was used to predict hypocalcemia based on the diagnostic criteria. Sensitivity and specificity were then calculated based on different cutoff points from the logistic regression model. Receiver operator curves were plotted with sensitivity vs 1-specificity. The cutoff point with maximum sensitivity was chosen as optimal for this screening test. Diagnosis criteria included both absolute PTH change and percent change for the immediate postoperative time point and the 6-hours postoperative time point. Sex effect was also examined using logistic regression model.
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