title: Parathyroid hormone assay predicts hypocalcaemia after total thyroidectomy.
abstract: BACKGROUND
  Postoperative parathyroid gland function after total thyroidectomy (TT) has traditionally been monitored by the measurement of serum calcium concentrations. The purpose of this study is to determine whether measurement of parathyroid hormone (PTH) concentrations in the early postoperative period accurately predicts patients at risk of developing hypocalcaemia.
  
  
  METHODS
  A prospective cohort study of patients undergoing TT was carried out. PTH concentrations were measured preoperatively and at 4 and 23 h postoperatively. Serum calcium concentration was measured preoperatively and twice daily for 48 h after surgery.
  
  
  RESULTS
  One hundred patients undergoing TT were recruited into the study in the period June 2004 to July 2005. Benign multinodular goitre was the most common indication for surgery (77%). The incidence of temporary hypocalcaemia (Ca < 2.0 mmol/L) was 18%. The mean PTH concentration at 4 h after surgery was 22.3 ng/L and was not significantly different from the 23-h concentration of 23.2 ng/L (P = 0.18). A PTH concentration of < or = 3 ng/L measured at 4 h after surgery had a sensitivity, specificity and likelihood ratio of 0.71, 0.94 and 11.3, respectively, for predicting postoperative hypocalcaemia. The accuracy of a single PTH concentration at 4 h was good for predicting hypocalcaemia (area under receiver-operator characteristic curve 0.90; confidence interval 0.81-0.96). There was no significant difference in accuracy between the 4- and 24-h PTH concentrations (P = 0.14).
  
  
  CONCLUSIONS
  A single measurement of PTH concentration in the early postoperative period after TT reliably predicts patients who are likely to develop hypocalcaemia. This approach facilitates early discharge and may decrease the need for multiple postoperative blood tests.
authors.affiliation: Department of Surgery, University of Sydney Endocrine Surgical Unit, Royal North Shore Hospital, St Leonards, New South Wales, Australia. marksywak@nebsc.com.au
authors.forename: Mark S
authors.initials: MS
authors.lastname: Sywak
authors.forename: Fausto F
authors.initials: FF
authors.lastname: Palazzo
authors.forename: Michael
authors.initials: M
authors.lastname: Yeh
authors.forename: Margaret
authors.initials: M
authors.lastname: Wilkinson
authors.forename: Kylie
authors.initials: K
authors.lastname: Snook
authors.forename: Stan B
authors.initials: SB
authors.lastname: Sidhu
authors.forename: Leigh W
authors.initials: LW
authors.lastname: Delbridge
mesh_terms: D000328:Adult; D002118:Calcium / Q000097:blood; D005260:Female; D006044:Goiter, Nodular / Q000601:surgery; D006801:Humans; D006996:Hypocalcemia / Q000175:diagnosis*; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D011183:Postoperative Complications; D012680:Sensitivity and Specificity; D013965:Thyroidectomy
chemical_list: D010281:Parathyroid Hormone; D002118:Calcium