Vitamin D Levels May Predict PTH Drop After Thyroid Cancer Surgery

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by Vanda Pinto, PhD |

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Vitamin D levels can accurately predict reductions in parathyroid hormone (PTH) following thyroidectomy in patients with papillary thyroid cancer (PTC), a study reports.

Its researchers recommend vitamin D supplements before surgery to minimize the drop in PTH levels in patients with PTC who have vitamin D deficiency.

The study, “Vitamin D Insufficiency Predicts Susceptibility of Parathyroid Hormone Reduction after Total Thyroidectomy in Thyroid Cancer Patients,” was published in the International Journal of Endocrinology.

PTC is a common type of thyroid cancer for which a total thyroidectomy, or removal of the thyroid gland, is often the recommended treatment. Accidental damage to the parathyroid glands during such surgery is one of the major causes of hypoparathyroidism, or low levels of PTH, and hypocalcemia (calcium deficiency). Other risk factors of post-surgery hypoparathyroidism — age, sex, and the presence of autoimmune diseases such as Graves’ disease — have also been suggested.

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Vitamin D helps the body absorb calcium and is typically prescribed to treat hypoparathyroidism. Some studies have reported an association between the lack of vitamin D before surgery and low levels of PTH. However, other researchers failed to confirm this finding.

Scientists in China set out to determine whether vitamin D levels, measured before a total thyroidectomy, can predict post-surgery hypoparathyroidism in patients with PTC.

“Our study is among the first few to investigate risk factors of postoperative PTH reduction ratio,” the researchers wrote.

Adult patients who underwent surgery at the Cancer Hospital of the University of Chinese Academy of Sciences between June 2016 and December 2017 were enrolled. Participants with other health conditions were excluded from the study, along with those taking daily vitamin D supplements. All parathyroid glands were preserved during surgery.

A total of 242 patients (190 women and 52 men) met the study criteria. Their median levels of PTH were 44.04 picograms (pg)/mL before, and 19.13 pg/mL after surgery. This represented a 56.6% decline in PTH levels following surgery.

None of the patients developed permanent post-surgery hypoparathyroidism, which is defined as hypoparathyroidism for more than six months. Ninety-nine participants (40.9%) had transient hypoparathyroidism, with their low levels of PTH persisting for less than six months. The majority of patients (76.9%) had vitamin D deficiency.

Next, the team searched for differences post-surgery between patients with hypoparathyroidism and those with normal PTH levels. They found that PTH levels were already low in the hypoparathyroidism group before surgery (42.83 vs. 47.52 pg/ml). No differences in several other parameters were detected, including sex, age, pre-surgery calcium levels, or vitamin D deficiency.

Patients were also divided based on their delta PTH, which is defined as the post-surgery PTH reduction ratio. Participants with post-surgery PTH levels that had been reduced by 50% or more were compared to those with post-surgery PTH levels that had fallen by less than 50%.

Those whose PTH levels had decreased by more than 50% after surgery had a lower mean vitamin D level. Additionally, a significantly larger proportion of women (83.3% vs. 71.4%) and vitamin D deficient patients (82.6% vs. 68.4%) were in this group.

Further analysis revealed that only vitamin D deficiency was associated with post-surgery delta PTH. “Vitamin D insufficient patients were 2.2 times more likely to have a postoperative PTH reduction ratio of more than 50%,” the investigators wrote.

PTH levels after surgery, as well as the delta PTH, were found to be good predictors of post-surgery hypocalcemia. A post-surgery PTH concentration of 14.0 pg/mL, and a delta PTH of 60%, were established as cut-off values to identify patients at risk of hypocalcemia.

The researchers noted that further studies are needed to determine appropriate doses of vitamin D supplements before surgery.