Dear Editors,

We recently came across the article titled ‘Analysis of the incidence and factors predictive of inadvertent parathyroidectomy during thyroid surgery’, by Hone et al.,Reference Hone, Tikka, Kaleva, Hoey, Alexander and Balfour ¹ in your esteemed journal. Firstly, we would like to commend the authors on a well thought out and well written article. While the article addresses many important issues regarding the relatively common problem of inadvertent parathyroidectomy, we would like to add a few points which we feel could further enrich the content of the paper.

Preservation of all parathyroid glands decreases transient hypoparathyroidism compared with when three or fewer glands are preserved, but does not affect permanent hypoparathyroidism. A study by Song et al. showed that during total thyroidectomy, preserving at least one parathyroid gland with an intact blood supply appeared to be sufficient to prevent permanent hypoparathyroidism when autotransplantation was not performed.Reference Song, Jung, Ji, Min, Ahn and Tae ² Yet, even if the single preserved parathyroid appears to be viable, it may become non-functioning, leading to post-operative hypoparathyroidism. Paek et al. found that lack of experience was a statistically significant risk factor for permanent hypoparathyroidism on multivariate analysis,Reference Paek, Lee, Min, Kim, Chung and Youn ³ and this point should be kept in mind during post-graduate training.

Various studies have shown that estimation of post-operative parathyroid hormone (PTH) levels on the day following a total thyroidectomy is an effective strategy to detect hypoparathyroidism, and that a low PTH level on day 1 is associated with a high risk of permanent hypoparathyroidism.Reference Almquist, Hallgrimsson, Nordenstrom and Bergenfelz ⁴ However, intra-operative PTH levels are not monitored routinely in thyroid surgery, although they are used widely during parathyroidectomy as an indicator of parathyroid gland function. Quiros et al. studied the use of intra-operative PTH levels as a predictive factor for post-operative hypoparathyroidism and found that an intra-operative PTH level of less than 10 pg/ml at closure was a strong predictor.Reference Quiros, Pesce, Wilhelm, Djuricin and Prinz ⁵ The authors suggested that these patients should be placed on vitamin D supplementation after surgery to avoid anticipated symptomatic hypocalcaemia.

Lastly, we would like to add a few words on the use of pre-operative serum vitamin D levels as a predictive factor for post-operative hypocalcaemia. A study by Tripathi et al., published in 2014, found that pre-operative serum vitamin D levels have a positive correlation with serum calcium levels in the early post-operative period.Reference Tripathi, Karwasra and Parshad ⁶ The study also showed that patients with serum vitamin D levels of less than 20 ng/ml were likely to develop early post-operative hypocalcaemia. Hence, it might be worthwhile for surgeons to consider the use of pre-operative serum vitamin D levels and intra-operative PTH levels as predictive factors for post-operative hypoparathyroidism in patients undergoing thyroid surgery.