Background: Hypocalcemia is common after thyroid surgery. Identification of risk factors predictive of post-thyroidectomy hypocalcemia can be used to select patients that may benefit from early routine calcium supplementation postoperatively to prevent symptoms from ever developing. The ability to predict who are the patients at risk for hypocalcemia would enable physicians to do close monitoring of these patients. Also, patients more likely to remain normocalcemic can have early but safe discharge.
Objective: To identify clinical predictors for post-thyroidectomy hypocalcemia among patients who undergo thyroidectomy at the Philippine General Hospital (PQH) from January 2000 to December 2003.
General Study Design: Retrospective Cohort Study.
Participants: Patients >/- 18 years old, who underwent thyroidectomy at PGH.
Intervention: Risk factors investigated were those identified in previous studies. These are: (1) Clinical Factors: Female sex, age, smoking, alcohol intake, menopause, thyroid cancer and toxic goiter, low pre-operative calcium level (2) Surgical Factors: Bilateral operation (OR), lymph node dissection (LN), repeat thyroid surgery, large goiter (>55 grams), operation time, blood loss and surgical expertise and specialty.
Outcome Measures: (1) Independent risk predictors for post-thyroidectomy hypocalcemia (2) Prevalence of symptomatic, asymptomatic and overall post-thyroidectomy hypocalcemia (Serum Calcium <2.12 mmol/L or ionized calcium <1.1 mmol/L).
Analysis: T test, Chi Square, Fisher's Exact test, Sensitivity/Specificity/Negative predictive value/ Positive Predictive value calculation, Logistic Regression.
Results: Three Hundred Sixty-three subjects (mean age 41 sd 13 years, 84.30 percent females) were included. One hundred thirteen (113, 31 percent) had symptoms of hypocalcemia postoperatively, 58 (16 percent) of which had low calcium levels (true hypocalcemia), 38 (10 percent) with normal calcium levels and 17 (4 percent) with no documented calcium level. Asymptomatic hypocalcemia occurred in 71 (26 percent) subjects. Bilateral operation and age <40 are independent predictors of symptomatic hypocalcemia, p<0.05[OR: 4.56 (95 percent CI:2.12-9.80) and 1.04 (95 percent CI:1.02-1.07) respectively. Clinical symptoms have low scores on all measures of validity.
Conclusion: Posthyroidectomy hypocalcemia is common (21 percent) after thyroid surgery. Bilateral operation and young age (<40 years old) are independent predictors of symptomatic hypocalcemia and overall post-thyroidectomy hypocalcemia.