Parathyroid hormone levels 4 hours after surgery do not accurately predict post-thyroidectomy hypocalcemia.
BACKGROUND
We evaluated the reliability of intact parathyroid hormone (iPTH) levels 4 hours after thyroidectomy (4h-iPTH) as a predictor of hypocalcemia in a large series of patients.


METHODS
A prospective experimental design involving 523 consecutive patients between September 1, 2004, and June 30, 2005, was employed. The specificity, sensitivity, and overall accuracy of 4h-iPTH in predicting post-thyroidectomy hypocalcemia and symptoms were determined.


RESULTS
A total of 199 patients developed hypocalcemia (serum calcium concentrations <8.0 mg/dl). Five patients still were receiving vitamin D/oral calcium at 6 months after the operation. Seventy-three patients experienced mild symptoms. The 4h-iPTH levels were reduced in hypocalcemic patients (28.8 +/- 15.3 vs 11.2 +/- 11.6 pg/ml) (P < .001). The 4h-iPTH levels were within the normal range (10 to 65 pg/ml) in 360 patients (290 normocalcemic) and subnormal in 163 patients (129 hypocalcemic, of whom 62 were symptomatic). The accuracy of 4h-iPTH levels <10 pg/ml in predicting post-thyroidectomy hypocalcemia and symptoms was 80.1% and 78.6%, respectively. False-negative results were observed in 70 hypocalcemic patients (13.4%), 11 of whom were symptomatic (2.1%).


CONCLUSIONS
Subnormal 4h-iPTH levels alone did not accurately predict clinically relevant postoperative hypocalcemia. The optimal cut-off level and its integration with preoperative and postoperative serum calcium concentrations should be reconsidered.
Lombardi
Celestino Pio
CP
Division of Endocrine Surgery, Università Cattolica del Sacro Cuore, Rome, Italy.
Raffaelli
Marco
M
Princi
Pietro
P
Dobrinja
Chiara
C
Carrozza
Cinzia
C
Di Stasio
Enrico
E
D'Amore
Annamaria
A
Zuppi
Cecilia
C
Bellantone
Rocco
R
D000293:Adolescent; D000328:Adult; D000368:Aged; D002118:Calcium / Q000097:blood; D005260:Female; D006801:Humans; D006996:Hypocalcemia / Q000097:blood* / Q000175:diagnosis / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D011184:Postoperative Period; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013965:Thyroidectomy / Q000009:adverse effects*; D013997:Time Factors
D010281:Parathyroid Hormone; D002118:Calcium