Systematic review and meta-analysis of predictors of post-thyroidectomy hypocalcaemia (Br J Surg 2014; 101: 307–320)

Sir Edafe and colleagues reported an interesting systematic review and meta-analysis of predictors of post-thyroidectomy hypocalcaemia (PTH). They established biochemical and clinical predictors of PTH, but we think that some points need to be clarified. We would like to point out that the study could have used post-thyroidectomy serum phosphate as a predictor of PTH. Patients developing significant hypocalcaemia certainly have hypoparathyroidism secondary to collateral surgical damage1,2. Two aspects of the problem need to be clarified: early PTH, and late and permanent hypocalcaemia. Most cases of early PTH are due to parathyroid ‘stunning’ from dissection or to rapid skeletal uptake of calcium: ‘hungry bone syndrome’ and others. This group represents patients with transient postoperative hypocalcaemia, which is self-limiting in most instances and does not require treatment. Late and permanent hypocalcaemia is mostly due to hypoparathyroidism3,4. PTH is the predominant regulator of serum phosphate and any drop in concentration leads to an increase in serum phosphate level. It was established, during the first 3 days after thyroidectomy1,3, that a post-thyroidectomy phosphorus level of at least 40 mg/l (1·29 mmol/l) carried a high risk of permanent hypocalcaemia1, and can reliably predict the need to treat hypocalcaemia following thyroidectomy in patients without vitamin D deficiency when it is over 44·58 mg/l (1·44 mmol/l)2. Edafe and colleagues identified high postoperative phosphate as a biochemical factor in Table 1, but did not assess this factor. The measurement of serum phosphate is widely available and it is inexpensive compared with the other tests (PTH, 25-hydroxyvitamin D). Assessing both serum calcium and serum phosphate throughout the 3 days after thyroidectomy can predict the outcome of PTH and therefore facilitate its management. In the abstract, Edafe and co-workers comment that perioperative PTH, preoperative vitamin D and postoperative changes in calcium are biochemical predictors of PTH. We found no calculation or risk estimation of these factors according to the meta-analysis results in the full text.