Effect of calcium supplementation on severe hypocalcemia in patients with secondary hyperparathyroidism after total parathyroidectomy

Table 1 Patient characteristics

	All patients (n = 271)	Conventional CS group (n = 145)	Preventive CS group (n = 126)	P value
Male (n)	156 (57.6%)	95 (65.5%)	61 (48.4%)	0.489
Age (yr)	47.7 ± 11.1	47.4 ± 11.4	48.1 ± 10.7	0.577
BMI (kg/m2)	22.9 ± 3.8	23.2 ± 4.0	22.7 ± 3.7	0.407
Preoperative iPTH levels (pg/mL)	1838.61 ± 933.60	1773.38 ± 934.49	1932.33 ± 928.01	0.143
Preoperative serum calcium amounts (mmol/L)	2.58 ± 0.24	2.60 ± 0.25	2.55 ± 0.22	0.075
Preoperative serum phosphorus levels (mmol/L)	2.24 ± 0.57	2.24 ± 0.60	2.22 ± 0.53	0.775
Preoperative calcium-phosphorus ratio	5.75 ± 1.52	5.81 ± 1.58	5.67 ± 1.45	0.444
Preoperative ALP amounts (U/L)	412.22 ± 415.14	409.18 ± 399.46	416.58 ± 438.28	0.878

CS: Calcium supplementation; BMI: Body mass index; iPTH: Intact parathyroid hormone; ALP: Alkaline phosphatase.

Table 2 Postoperative characteristics

Variable	All patients (n = 271)	Conventional CS group (n = 145)	Preventive CS group (n = 126)	P value
Postoperative serum calcium levels (mmol/L)	1.91 ± 0.34	1.81 ± 0.32	2.02 ± 0.32	< 0.001
Patients with postoperative hypocalcemia (n, %)	166 (61.3)	108 (74.5)	58 (46.0)	< 0.001
Patients with postoperative SH (n, %)	133 (49.1)	93 (64.1)	40 (31.7)	< 0.001
Patients with postoperative critical hypocalcemia (n, %)	26 (9.6)	21 (14.5)	5 (4.)	0.003

CS: Calcium supplementation; SH: Severe hypocalcemia.

Table 3 Univariable analysis of factors associated with severe hypocalcemia in all patients

	Univariate
	t	χ2	P value
Sex	-	3.079	0.079
Age	3.533	-	< 0.001
BMI	0.181	-	0.856
Preoperative iPTH levels	-7.260	-	< 0.001
Preoperative ALP amounts	-6.800	-	< 0.001
Preoperative serum calcium amounts	1.520	-	0.130
Preoperative serum phosphorus levels	-2.872	-	0.004
Preoperative calcium-phosphorus ratio	-2.163	-	0.031
CS regimen	-	28.304	< 0.001

BMI: Body mass index; iPTH: Intact parathyroid hormone; ALP: Alkaline phosphatase; CS: Calcium supplementation.

Table 4 Multivariable analysis of risk factors for severe hypocalcemia in all patients

	Multivariate
	OR	95%CI	P value
Sex			0.447
Female	Ref
Male	1.275	0.682-2.381
Age	0.994	0.963-1.025	0.684
Preoperative iPTH levels	1.001	1.000-1.001	0.009
Preoperative ALP amounts	1.002	1.001-1.003	0.002
Preoperative serum phosphorus concentration	8.729	1.518-50.216	0.015
Preoperative calcium-phosphorus ratio	0.577	0.306-1.087	0.089
CS regimen
Conventional CS	Ref
Preventive CS	0.132	0.067-0.261	< 0.001

OR: Odds ratio; CI: Confidence interval; iPTH: Intact parathyroid hormone; ALP: Alkaline phosphatase; CS: Calcium supplementation; Ref: Reference.

Table 5 Hypocalcemia in patients with alkaline phosphatase ≥ 500 U/L

Variable	All patients (n = 77)	Conventional CS group (n = 42)	Preventive CS group (n = 35)	P value
Postoperative serum calcium levels (mmol/L)	1.65 ± 0.22	1.55 ± 0.17	1.76 ± 0.22	< 0.001
Patients with postoperative hypocalcemia (n, %)	72 (93.5)	41 (97.6)	31 (88.6)	0.171
Patients with postoperative SH (n, %)	60 (77.9)	38 (90.5)	22 (62.9)	0.005
Patients with postoperative critical hypocalcemia (n, %)	17 (22.1)	14 (33.3)	3 (8.6)	0.012

CS: Calcium supplementation; SH: Severe hypocalcemia.

Table 6 Multivariate analysis of risk factors for severe hypocalcemia in patients with preoperative alkaline phosphatase > 500 U/L

	Multivariate
	OR	95%CI	P value
Sex			0.142
Female	Ref
Male	2.610	0.726-9.380
Age	0.993	0.938-1.050	0.795
Preoperative iPTH levels	1	0.999-1.001	0.965
Preoperative ALP amounts	1.001	0.999-1.003	0.202
Preoperative serum phosphorus concentration	3.851	0.094-157.237	0.877
Preoperative calcium-phosphorus ratio	0.848	0.227-3.168	0.973
CS regimen
Conventional CS	Ref
Preventive CS	0.147	0.038-0.562	0.005

OR: Odds ratio; CI: Confidence interval; iPTH: Intact parathyroid hormone; ALP: Alkaline phosphatase; CS: Calcium supplementation; Ref: Reference.