PTH Levels Predict Low Calcium After Thyroid Surgery, Can Guide Treatment

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by Steve Bryson, PhD |

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PTH levels and calcium deficiency

Levels of parathyroid hormone (PTH) accurately predicted hypoparathyroidism-related calcium deficiency following surgery to remove the thyroid gland, a study reported. 

A PTH cut-off value was established to identify those at risk, who were started on calcium and vitamin D supplements. Such prompt treatment eased symptoms and allowed for an earlier hospital discharge, its researchers noted. 

The study, “The optimal parathyroid hormone cut-off threshold for early and safe management of hypocalcemia after total thyroidectomy,” was published in the journal Endocrine Practice.

Unintentional damage to the parathyroid glands during surgery to remove the thyroid gland (thyroidectomy) can lead to hypoparathyroidism — low levels of PTH — which is associated with calcium deficiency, or hypocalcemia. PTH also regulates phosphorus and vitamin D levels. 

As such, surgeons need to identify patients at risk of such deficiencies and begin treatment approaches to avoid manifestations of hypocalcemia, including muscle spasms, cramps, and abnormal skin sensations (tingling and numbness).

Researchers at the Jordan Hospital, in Jordan, designed a study to define the postoperative cut-off value of PTH that would predict hypocalcemia and allow timely therapy in people at risk.

The study was conducted in two phases: the first phase analyzed various predictors of symptomatic hypocalcemia to define the optimal PTH cut-off threshold. The second phase focused on the benefits of postoperative calcium and vitamin D supplements given to those whose PTH level fell below the calculated threshold. 

A total of 175 patients were included in the first phase and 178 in the second, with an overall mean age of 42.7. A total of 260 participants (73.7%) were women, and 93 (26.3%) were men.

Based on the presence or absence of hypocalcemia symptoms, people in the first phase were classified into two groups to identify predictors within 24 hours of thyroid surgery. 

The analysis found no significant difference between the two groups when comparing sex, age, nationality, cause of thyroid disease, type of surgery, unintended removal of parathyroid, and postoperative calcium levels. The only predictor of hypocalcemia symptoms was PTH level. 

Statistical analysis showed a PTH level of 19.95 picograms per mL (pg/mL) to be the optimal cut-off point, with an area under the curve (AUC) of 0.903, in which values above 0.9 are considered highly accurate. 

This cut-off value had a 100% sensitivity, a test’s ability to identify those at risk correctly, and a 71.8% specificity, in which a negative test indicates no risk. In contrast, a cut-off value of 14.95 pg/mL showed 73.7% sensitivity and 80.2% specificity. 

Participants with PTH above the optimal threshold of 19.95 pg/mL were considered low-risk, while those up to this value were deemed high-risk for postoperative hypocalcemia and prompt treatment. 

Of the 175 first phase participants, 112 (64%) were classified as low risk based on PTH cut-off, with none showing hypocalcemia symptoms, and all were discharged 24 hours after surgery with no need for supplements. None of these patients required further intervention. 

The remaining 63 patients (36%) were classified as high risk, with 52 not showing postoperative hypocalcemia and discharged with no supplementation. Of these, eight returned to the emergency department within 72 hours and were given calcium supplements with calcium gluconate then calcium carbonate, as well as alfacalcidol (active form of vitamin D). The 11 high-risk patients with hypocalcemia symptoms were immediately given calcium carbonate and alfacalcidol.

After applying the calculated PTH cut-off value to second phase patients, 66 out of 178 (37.1%) were classified as high-risk and were immediately treated with supplemental calcium carbonate and alfacalcidol regardless of the presence or absence of hypocalcemia symptoms. All of these patients were discharged 24 hours after surgery. 

Hypocalcemia occurred in five patients (7.6%) within the first 24 hours, and symptomatic hypocalcemia after hospital discharge was reported in two patients (3%) who required calcium. None of the second phase patients were re-admitted to hospital. 

An analysis of all patients in both phases showed that prompt treatment led to significant reduction in symptomatic hypocalcemia. High-risk participants had a significant decrease in symptomatic hypocalcemia as high as 30% in first phase patients. 

“This strategy allowed safe 24-hour discharge post-[thyroidectomy] in all patients in both phases of the study,” the team wrote. 

None of those with PTH levels above the cut-off value developed symptoms, returned to hospital after discharge, or required further treatment. 

A comparison of pre- and post-surgery PTH showed that, out of 112 low-risk patients, 41 (36.7%) had postoperative increases. An analysis of those with higher PTH did not identify any significant parameter to explain this finding.

A final examination of vitamin D levels in second phase participants showed 65 with a deficiency before surgery. The same patients showed significantly higher levels after surgery (greater than 20 ng/mL) while postoperative calcium levels were not affected. Overall, vitamin D levels in second phase patients were similar to healthy individuals. 

“Low-risk patients were discharged with no supplementation while all high-risk patients received prompt calcium and vitamin D supplementation, which led to effective hypocalcemia management and safe 24-hour discharge,” the scientists wrote.