[Serum PTH levels as a predictive factor of hypocalcaemia after total thyroidectomy]. / Determinación de paratirina en suero como factor predictivo de hipocalcemia tras tiroidectomía total.

INTRODUCTION: Postoperative parathyroid hormone (PTH) levels as a predictor of hypocalcaemia in patients subjected to total thyroidectomy is analyzed. MATERIAL AND METHOD: Prospective study involving 67 patients who underwent total thyroidectomy due to a benign disease. Serum PTH and ionised calcium were measured 20 h after surgery. Sensitivity, specificity and predictive values of PTH and ionised calcium levels were calculated to predict clinical and analytical hypocalcaemia. RESULTS: A total of 42 (62.7%) patients developed hypocalcaemia (ionised calcium<0.95 mmol/l), but only 20 (29.9%) presented with symptoms. PTH concentration the day after surgery was significantly lower in the group that developed symptomatic hypocalcaemia (5.57+/-6.4 pg/ml) than in the asymptomatic (21.5+/-15.3 pg/ml) or normocalcaemic (26.8+/-24.9 pg/ml) groups (p=0.001). Taking the value of 13 pg/ml as a cut-off point of PTH levels, sensitivity, specificity, positive predictive value and negative predictive value were 54%, 72%, 76% and 48%, respectively. On the other hand, sensitivity for predicting symptomatic hypocalcaemia was 95% and specificity was 76%. The test showed a high incidence of false positives (11/30, 36%). Negative predictive value was 97% and positive predictive value was 65%. In multivariate analysis, PTH and ionised calcium were the only perioperative factors that showed an independent predictive value as risk indicators of symptomatic hypocalcaemia. CONCLUSIONS: Normal PTH levels 20 h after surgery practically rule out the subsequent appearance of hypocalcaemia symptoms. On the other hand, low PTH levels are not necessarily associated to symptomatic hypocalcaemia due to the high number of false positives.

Determinación de paratirina en suero como factor predictivo de hipocalcemia tras tiroidectomía total / Serum PTH levels as a predictive factor of hypocalcaemia after total thyroidectomy

Introducción: se analiza el valor de la determinación postoperatoria de paratirina como indicador de riesgo de hipocalcemia tras tiroidectomía total. Material y método: estudio prospectivo de 67 pacientes sometidos a tiroidectomía total por enfermedad benigna. Se determinó la concentración de paratirina y calcio iónico a las 20h de postoperatorio. Se calculó la sensibilidad, la especificidad y los valores predictivos positivo (VPP) y negativo (VPN) de las concentraciones de paratirina y calcio iónico para predecir la aparición de hipocalcemia sintomática o no. Resultados: presentaron hipocalcemia (Ca iónico<0,95 mmol/l) 42 pacientes (62,7%) pacientes, pero únicamente 20 (29,9%) mostraron síntomas. La concentración de paratirina a las 20h de la intervención fue inferior en el grupo con hipocalcemia sintomática (5,57±6,4pg/ml) que en el grupo de hipocalcemia sin síntomas (21,5±15,3pg/ml) y que entre los pacientes normocalcémicos (26,8±24,9pg/ml) (p=0,001). Con un punto de corte para la paratirina en 13pg/ml, la sensibilidad, la especificidad, el VPP y el VPN de paratirina para predecir la aparición de hipocalcemia analítica fueron del 54, el 72, el 76 y el 48%, respectivamente. Por otro lado, la sensibilidad para predecir hipocalcemia sintomática fue del 95% y la especificidad, el 76%. El test presentó alta incidencia de falsos positivos (11/30) (36%). El VPN fue del 97% y el VPP, el 65%. Paratirina y calcio iónico en el análisis multivariable fueron los únicos factores con valor predictivo como indicadores de riesgo de hipocalcemia sintomática. Conclusiones: una concentración normal de paratirina a las 20h de la intervención prácticamente descarta la aparición posterior de síntomas de hipocalcemia. Por contra, cifras de paratirina bajas no se acompañan necesariamente de síntomas debido al elevado número de falsos positivos (AU)

Introduction: Postoperative parathyroid hormone (PTH) levels as a predictor of hypocalcaemia in patients subjected to total thyroidectomy is analyzed. Matherial and method: Prospective study involving 67 patients who underwent total thyroidectomy due to a benign disease. Serum PTH and ionised calcium were measured 20h after surgery. Sensitivity, specificity and predictive values of PTH and ionised calcium levels were calculated to predict clinical and analytical hypocalcaemia. Results: A total of 42 (62.7%) patients developed hypocalcaemia (ionized calcium<0.95mmol/l), but only 20 (29.9%) presented with symptoms. PTH concentration the day after surgery was significantly lower in the group that developed symptomatic hypocalcaemia (5.57±6.4pg/ml) than in the asymptomatic (21.5±15.3pg/ml) or normocalcaemic (26.8±24.9pg/ml) groups (p=0.001). Taking the value of 13pg/ml as a cut-off point of PTH levels, sensitivity, specificity, positive predictive value and negative predictive value were 54%, 72%, 76% and 48%, respectively. On the other hand, sensitivity for predicting symptomatic hypocalcaemia was 95% and specificity was 76%. The test showed a high incidence of false positives (11/30, 36%). Negative predictive value was 97% and positive predictive value was 65%. In multivariate analysis, PTH and ionised calcium were the only perioperative factors that showed an independent predictive value as risk indicators of symptomatic hypocalcaemia. Conclusions: Normal PTH levels 20h after surgery practically rule out the subsequent appearance of hypocalcaemia symptoms. On the other hand, low PTH levels are not necessarily associated to symptomatic hypocalcaemia due to the high number of false positives (AU)