The role of early postoperative parathyroid hormone level after total thyroidectomy in prediction of hypocalcemia

Chapter 14: Post surgical follow-up of primary hyperparathyroidism

Primary hyperparathyroidism is treated surgically. Postoperatively, close monitoring of blood calcium levels is necessary to detect any hypocalcemia. Postoperative PTH assays can be performed within 24hours to identify patients who will not develop permanent hypoparathyroidism. Hypocalcemia may be caused by hypoparathyroidism (especially in the case of multi-glandular surgery or revision surgery) or by hungry bone syndrome. The latter should be suspected in case of major skeletal damage or severe preoperative vitamin D deficiency. It leads to severe hypocalcemia with normal or elevated PTH concentration, hypophosphatemia, hypomagnesemia, and low calciuria despite high doses of calcium and 1-25 OH vitamin D. Treatment of postoperative hypocalcemia depends on severity, symptoms and surgical procedure. In uni-glandular surgery, symptomatic treatment with calcium alone is recommended (0.5 to 1g/day). In multi-glandular involvement or repeat surgery, treatment with calcium (1 to 3g/day) is recommended if hypocalcemia is symptomatic or profound (<1.9mmol/L) (i.e. 76mg/L). If it is insufficient, the potential contribution of active vitamin D treatment should be assessed with an endocrinologist. If hypocalcemia is treated, patients should preferably be monitored by an endocrinologist (blood calcium level, calciuria and possibly phosphatemia and PTH). Under medical treatment of hypoparathyroidism, blood calcium levels should be monitored at least every 3 months for the first year, then at least twice a year.

Predictive value of 6 h postoperative parathyroid hormone level on permanent hypoparathyroidism in pediatric total thyroidectomy: a pilot study

OBJECTIVES

Transient hypocalcemia is a common complication after pediatric total thyroidectomy, while permanent hypoparathyroidism (PH) is relatively uncommon. To date there is no model to predict which patients will develop PH based on post-operative makers. We aim to identify pediatric patients who are at high risk of PH following thyroidectomy based on 6 h post-operative parathyroid hormone (PTH) value.

METHODS

A retrospective review of 122 pediatric patients undergoing total thyroidectomy between 2016 and 2022 following implementation of a multidisciplinary team was performed. Outcome of interest was permanent hypoparathyroidism, defined as need for calcium supplementation at 6 months postoperatively. Receiver operating characteristic (ROC) analysis was used to determine PTH value at 6 h post-operative that was predictive of permanent hypoparathyroidism.

RESULTS

Rates of permanent hypoparathyroidism reported are similar to those described in the literature with 12 patients (10.9%) developing PH. In patients who developed PH, mean 6 h postoperative PTH was 5.12 pg/mL. Mean 6 h postoperative PTH level in those who did not develop PH was 31.34 pg/mL (p<0.0001). The 6 h post-operative PTH value predictive for PH was ≤11.3 pg/mL. PTH cutoff of ≤11.3 pg/mL had a sensitivity of 100%, specificity of 72.2%, positive predictive value (PPV) of 27.0%, and negative predictive value (NPV) of 100%.

CONCLUSIONS

6 h postoperative PTH values were found to be predictive of permanent hypoparathyroidism in pediatric total thyroidectomy: a 6 h postoperative PTH level of >11.3 pg/mL excludes permanent hypoparathyroidism, but if PTH is ≤11.3 pg/mL at 6 h, approximately 1/3 of patients may persist with permanent hypoparathyroidism.

Definition and diagnosis of postsurgical hypoparathyroidism after thyroid surgery: meta-analysis

BACKGROUND

Postsurgical hypoparathyroidism (PH) is the most frequent complication after thyroid surgery. The aim of this systematic review and meta-analysis is to summarize a unifying definition of PH and to elucidate the best possible approach for early detection of PH.

METHODS

A systematic review of the literature according to the PICO framework using Embase, PUBMED and the Cochrane library was carried out on 1 December 2021 followed by analysis for risk of bias, data extraction and meta-analysis. All studies addressing the definition of postoperative hypoparathyroidism and/or diagnostic approaches for early detection and diagnosis were included. Case reports, commentaries, non-English articles, book chapters and pilot studies and reviews were excluded.

RESULTS

From 13 704 articles, 188 articles were eligible for inclusion and further analysis. These articles provided heterogeneous definitions of PH. Meta-analysis revealed that postoperative measurements of parathormone (PTH) levels have a higher sensitivity and specificity than intraoperative PTH measurements to predict PH after thyroid surgery. None of the timeframes analysed after surgery within the first postoperative day (POD1) was superior to predict the onset of PH. PTH levels of less than 15 pg/ml and less than 10 pg/ml are both reliable threshold levels to predict the postoperative onset of PH. A relative reduction of mean(s.d.) PTH levels from pre- to postoperative values of 73 (standard deviation 11) per cent may also be predictive for the development of PH. The estimation of calcium levels on POD1 are recommended.

CONCLUSION

PH is best defined as an undetectable or inappropriately low postoperative PTH level in the context of hypocalcaemia with or without hypocalcaemic symptoms. PTH levels should be measured after surgery within 24 h. Both threshold levels below 10 and 15 pg/ml or relative loss of PTH before/after thyroid surgery are reliable to predict the onset of PH.