title: Serum phosphate predicts temporary hypocalcaemia following thyroidectomy.
abstract: BACKGROUND
  Temporary hypocalcaemia occurs in up to 40% of patients following a total thyroidectomy. Serum calcium and parathyroid hormone (PTH) measurements are currently used to predict post-thyroidectomy hypocalcaemia. However, immediate access to PTH measurement is expensive and not widely available. Serum phosphate responds rapidly to changes in circulating PTH levels, and its measurement is readily available in all hospitals. We evaluated the use of serum phosphate to predict temporary hypocalcaemia post-thyroidectomy.
  
  
  METHODS
  We retrospectively assessed 111 consecutive patients who had total or completion thyroidectomy. Patients had serum calcium and phosphate measured preoperatively, on the evening of surgery (day 0), on the morning of day 1 and over the following week as clinically indicated. Serum PTH was measured on the morning of day 1. Vitamin D levels were measured preoperatively.
  
  
  RESULTS
  Seventy-six patients did not develop treatment-demanding hypocalcaemia. In these patients, the mean serum phosphate concentration was lower on the morning of day 1 compared to that on the evening of surgery. Seventeen patients with a vitamin D>25 nmol/l developed hypocalcaemia requiring treatment from day 1 onwards. All had an overnight rise in serum phosphate to >1.44 mmol/l (100% sensitivity and specificity for predicting hypocalcaemia). Twelve patients who had a vitamin D<25 nmol/l also developed hypocalcaemia but had an attenuated rise in serum phosphate.
  
  
  CONCLUSIONS
  Serum phosphate is a reliable biochemical predictor of post-thyroidectomy hypocalcaemia in patients without vitamin D deficiency. The use of serum phosphate may facilitate safe day 1 discharge of patients undergoing thyroidectomy.
authors.affiliation: Division of Diabetes, Endocrinology and Metabolism, Hammersmith Hospital, Imperial College London, London, UK.
authors.forename: Amir H
authors.initials: AH
authors.lastname: Sam
authors.forename: W S
authors.initials: WS
authors.lastname: Dhillo
authors.forename: M
authors.initials: M
authors.lastname: Donaldson
authors.forename: A
authors.initials: A
authors.lastname: Moolla
authors.forename: K
authors.initials: K
authors.lastname: Meeran
authors.forename: N S
authors.initials: NS
authors.lastname: Tolley
authors.forename: F F
authors.initials: FF
authors.lastname: Palazzo
mesh_terms: D002118:Calcium / Q000097:blood; D006801:Humans; D006996:Hypocalcemia / Q000097:blood / Q000175:diagnosis / Q000209:etiology*; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000097:blood*; D011183:Postoperative Complications / Q000097:blood / Q000175:diagnosis / Q000209:etiology*; D011237:Predictive Value of Tests; D011379:Prognosis; D012189:Retrospective Studies; D013965:Thyroidectomy / Q000009:adverse effects* / Q000379:methods; D013997:Time Factors; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood
chemical_list: D010281:Parathyroid Hormone; D010710:Phosphates; D014807:Vitamin D; C104450:25-hydroxyvitamin D; D002118:Calcium