Accuracy of postthyroidectomy parathyroid hormone and corrected calcium levels as early predictors of clinical hypocalcemia.

ABSTRACTObjective: To evaluate the accuracy of measurement of different parathyroid hormone (PTH) and corrected calcium (cCa) levels atdifferent times as early predictors of postthyroidectomy hypocalcemia.Design: A retrospective cohort study.Setting: King Fahad Medical City, Riyadh, Saudi Arabia, between January 2006 and March 2009.Methods: Patients who underwent total or completion thyroidectomy were followed until hospital discharge. Patients wereobserved clinically for hypocalcemia; at the same time, the postoperative PTH and cCa levels after 6, 12, and 20 hours and then twicedaily were recorded.Main Outcome Measures: Postthyroidectomy hypocalcemia.Results: Seventy-nine of 116 patients were enrolled in our study; 26.60% of them had hypocalcemia. PTH measurement at 6hours postoperatively was an excellent predictor of hypocalcemia (area under the curve 5 0.95, 95% CI 0.88–0.99). The mean PTH at 6hours for hypocalcemic patients was 0.93 (6 0.60). A 1.7 pmol/L as a cutoff level of PTH at 6 hours has 95.2% sensitivity, 89.7%specificity, 76.9% positive predictive value (PPV), and 98.1% negative predictive value (NPV). On the other hand, a 2.1 mmol/L as acutoff level of cCa has 81.0% sensitivity, 81.6% specificity, 65.3% PPV, and 90.9% NPV in predicting hypocalcemic patients.Conclusions: PTH measurement 6 hours after surgery with a cutoff level of 1.7 pmol/L is more accurate than serial calcium levelmeasurement for early prediction of patients at risk of hypocalcemia. Thus, a single PTH measurement postoperatively will help indischarging patients safely within the first 24 hours, improving bed use and cost-effective care.SOMMAIREObjectif: L’e´tude avait pour objectif d’e´valuer la fiabilite´ de la mesure des taux de parathormone (PTH) et de calcium corrige´ (Cac)comme facteur pre´dictif pre´coce d’hypocalce´mie clinique apre`s thyroi¨dectomie.Type d’e´tude: Il s’agit d’une e´tude de cohortes, re´trospective.Lieu: L’e´tude a e´te´ mene´e a` l’hoˆpital King Fahad Medical City, a` Riyad, en Arabie saoudite, entre janvier 2006 et mars 2009.Me´thodes: Des patients ayant subi une thyroi¨dectomie totale ou une thyroi¨dectomie comple´mentaire ont e´te´ suivis jusqu’aumoment du conge´ de l’hoˆpital. Ils ont fait l’objet d’observation clinique a` la recherche de signes d’hypocalce´mie; pendant ce temps,les taux de PTH et de Cac mesure´s 6 h, 12 h et 20 h apre`s l’ope´ration, puis 2 fois par jour, ont e´te´ consigne´s au dossier.Principaux crite`res d’e´valuation: Le principal crite`re d’e´valuation e´tait l’hypocalce´mie apre`s thyroi¨dectomie.Re´sultats: Soixante-dix-neuf patients sur 116 ont participe´a` l’e´tude, et 26.60% d’entre eux ont souffert d’hypocalce´mie. Lamesure du taux de PTH 6 heures apre`s l’ope´ration s’est re´ve´le´e un excellent facteur pre´dictif d’hypocalce´mie (surface sous la courbe5 0.95; IC a` 95%: 0.88–0.99). Le taux moyen de PTH au bout de 6 heures chez les patients hypocalce´miques s’est e´tabli a` 0.93 (6 0.60).D’une part, un taux seuil de 1.7 pmol/L pour la PTH, au bout de 6 heures, avait une sensibilite´ de 95.2%, une spe´cificite´ de 89.7%, unevaleur pre´dictive positive (VPP) de 76.9% et une valeur pre´dictive ne´gative (VPN) de 98.1%. D’autre part, un taux seuil de 2.1 mmol/LAddress reprint requests to: Saleh Fahad Al-Dhahri, MD, King FahadMedical City, Consultant Head and Neck Surgical Oncology, PO Box59046, Riyadh, Saudi Arabia 11525; e-mail: saldhahri@kfmc.med.sa.