Decrease in PTH Levels Right After Thyroidectomy Predicts Calcium Deficiency

Having a greater than 65% drop in parathyroid hormone (PTH) levels on the first day after a total thyroid removal increases the likelihood of developing transient calcium deficiency, or hypocalcemia, according to a single-center study in China.

People with hypocalcemia have lower than normal levels in their blood of calcium, a mineral needed for bone health, muscle movement, and healthy nerves.

The data, which came from patients with papillary thyroid carcinoma — the most common type of thyroid cancer — also highlighted that being a female and having a large tumor were additional independent risk factors for postoperative hypocalcemia.

Such findings suggest that clinicians should consider these parameters when deciding how to best manage or prevent postoperative hypocalcemia, and when to discharge patients undergoing total thyroid removal, the researchers said.

The study, “Parathyroid Hormone Reduction Predicts Transient Hypocalcemia after Total Thyroidectomy: A Single-Center Prospective Study,” was published in the International Journal of Endocrinology.

Surgery to completely remove the thyroid glands, called a total thyroidectomy, can lead to the unintentional removal of parathyroid glands tissue and to hypoparathyroidism, or low levels of the PTH.

A deficiency in PTH levels may, in turn, cause postoperative hypocalcemia, which is the most common complication following thyroidectomy.

Previous studies have shown that the risk of hypocalcemia is even greater when patients undergo thyroidectomy with central lymph node dissection (CLND), which is associated with lower cancer recurrence.

As such, the early prediction of hypocalcemia may help initiate timely treatment with calcium and vitamin D supplements, and reduce hospital stay.

However, with many cases being temporary and asymptomatic (without symptoms), determining who is most likely to develop this complication after surgery remains a difficult task.

Several studies have shown that measuring PTH levels or their reduction one day after surgery is a reliable way to predict the development of hypoparathyroidism. Others have highlighted that female patients have a higher risk for transient postoperative hypocalcemia than males do.

Now, researchers in China evaluated whether age, sex, tumor size, preoperative PTH and calcium blood levels, and a PTH drop on postoperative day one were risk factors of hypocalcemia following a total thyroidectomy with CLND for papillary thyroid carcinoma.

Data was analyzed from 176 patients — 137 women and 39 men — with a median age of 46, and a range in age from 17 to 73. A total of 155 participants underwent thyroidectomy with bilateral CLND, or the removal of all lymph nodes around the thyroid. The remaining 21 had ipsilateral CLND — the removal of nodes on the same side of the thyroid cancer — at the Zhejiang Cancer Hospital, in China. The study was conducted between January 2016 and June 2018.

The results showed that 51 patients (nearly 29%) developed transient hypocalcemia on postoperative day one and two patients (1.14%) showed permanent hypoparathyroidism over one year of follow-up.

Female patients or those showing a greater drop in PTH levels, greater tumor size, or lower preoperative calcium levels were significantly more likely to develop hypocalcemia one day after surgery.

No significant differences were found between patients undergoing bilateral and ipsilateral CLND, suggesting that the type of lymph node surgery does not influence postoperative PTH and calcium levels in these patients.

Further analyses confirmed that the PTH level drop, being female, and tumor size were independent risk factors for postoperative hypocalcemia in patients undergoing total thyroidectomy with CLND. No risk factors were identified in males.

Notably, a lower threshold of PTH-level reduction — a 65.58% drop in PTH levels — predicted with high accuracy the occurrence of transient hypocalcemia in all patients, compared with that in women and in individuals undergoing bilateral CLND (a 71% drop in both).

These differences suggest that bilateral CLND and being female “are factors that should be considered when predicting transient hypocalcemia in patients who undergo total thyroidectomy for [papillary thyroid carcinoma],” the researchers wrote.

The PTH drop threshold found for all patients was consistent with that reported in previous studies, the team said. In addition, large tumors predicted transient hypocalcemia in females, also when associated with a PTH reduction greater than 71%.

These findings suggested that additional risk factors should be considered in females undergoing total thyroidectomy with CLND, the scientists added.