Higher levels of PTH after LSG related to vitamin D deficiency

Higher levels of parathyroid hormone (PTH) after laparoscopic sleeve gastrectomy (LSG) can be related to vitamin D deficiency and lower calcium levels, despite patients following the provided recommendations for supplementation. The study, ‘Secondary Hyperparathyroidism in Obese Patients Post Sleeve Gastrectomy’, was published in Dove press, led by researchers from the King Saud University, Riyadh, Saudi Arabia, also accentuates the importance of routine testing for hyperparathyroidism both before and after bariatric surgery.

In their study, the authors sought to compare the levels of blood biomarkers (specifically, Ca, vitamin D and phosphate (PO4)), and their association with PTH levels in pre- and post-bariatric surgery. They also wanted to assess the prevalence of hyperparathyroidism post-bariatric surgery in a tertiary care hospital in Saudi Arabia. This is the only national study available to date to investigate such an association, the authors believe.


Data were collected from May 2017 to April 2019 and included adult (age ≥18 years) patients with obesity (BMI≥30kg/m2) undergoing LSG, however, patients were excluded if they were known to have any comorbidities (eg, diabetes mellitus, hypertension, hypercholesterolemia, or hypertriglyceridemia), using medications to treat chronic conditions, receiving any vitamin supplements or herbal product, and patients who had undergone bariatric surgery previously.

Routine blood tests including complete blood count (CBC), serum albumin, total protein, haemoglobin, PTH, vitamin D, corrected calcium (Ca), phosphate (PO4), renal profile, and bone quality measurement tests were collected pre-operatively and during follow-up visits at 12 to 18 months post-surgery.


Outcomes

In total, 143 patients who underwent LSG and met the study inclusion criteria were included in the study. All subjects had data available at baseline (pre-operatively) and 12–18 months follow-up (post-operatively). The mean age was 31.30±9.70 years, with the majority being females (58%). The pre-operative mean BMI was 44.95± 8.05 kg/m2.


Hyperparathyroidism was observed in 15.4% of patients at baseline and in 36.4% post-surgery (p<0.001). Low vitamin D levels, which were highly prevalent before surgery, decreased significantly (66.4% pre-operative and 28.0% at follow-up after surgery, p=0.032). Baseline hypocalcaemia was seen in 20.3% of patients vs. 8.4% post-surgery (p=0.546). Hypophosphatemia occurred in 60.8% of patients and was reduced to 31 patients (21.7%) post-surgery.


Pre-operatively, only baseline PO4 level was associated with PTH levels in univariate linear regression analysis and this association remained significant in multivariate analysis. Post-operatively, there was a significant correlation between PTH and both Ca and vitamin D, and remained significant in multivariate analysis.


The researcher then separated the patients into four groups according to their laboratory values and status before or after the surgery:

  • Group 1 consists of patients with SHPT pre-surgery

  • Group 2 includes patients without SHPT pre-surgery

  • Group 3 includes patients with SHPT post-surgery, and;

  • Group 4 includes patients without SHPT post-surgery.


Post-surgery, all groups had maintained normal phosphate-metabolism homeostasis and there was no statistically significant difference in vitamin D levels between patients with secondary hyperparathyroidism (SHPT) and patients without SHPT pre-operatively. However, a statistically significant increase in vitamin D levels was observed post-operatively, and this effect was predominant in patients without SHPT (p=0.011). Calcium levels were higher in patients with SHPT vs. patients without SHPT pre-operatively, however the difference did not reach a significant level. Post-operatively, calcium levels were significantly lower in patients with SHPT than in patients without SHPT.


When analysing the relationship between high PTH levels and clinical characteristics using logistic regression, none of the covariates were significantly associated with SHPT pre-operatively. Post-operatively, Ca, PO4 and vitamin D were significantly associated with SHPT in univariate analysis. However, only the relationship with Ca level remained significant in multivariate analysis.

The researchers noted that the most remarkable finding in their study was that 15% of the studied patients already had SHPT before surgery. They found that 66.4% of patients had pre-operative vitamin D deficiency.


“Our study showed a high rate of SHPT in patients undergoing LSG, which can be attributed to changes in vitamin D and calcium levels. Moreover, the study findings emphasize the importance of routine testing for hyperparathyroidism both before and after LSG,” the authors concluded. “An optimal regimen of calcium and vitamin D supplementations needs to be specified, and this would be an important area for further research.”


Further information

To access this paper, please click here