Risk of anemia in morbidly obese patients after bariatric surgery in Taiwan

Table 1 Demographic characteristics of patients diagnosed morbid obesity receiving and not-receiving bariatric surgery

Variable	Receiving bariatric surgery				P value1
	No [n = 1509 (34.51%)]		Yes [n = 2864 (65.49%)]
	n	%	n	%
Malabsorptive procedures	-	-	1773	61.91	-
Restrictive procedures	-	-	2465	86.07	-
Sex					< 0.0001
Female	818	54.21	1855	64.77
Male	691	45.79	1009	35.23
Age at baseline, yr					< 0.0001
20-29	302	20.01	1305	45.57
30-64	1034	68.52	1558	54.4
65-100	173	11.46	1	0.03
mean ± SD	44.30 ± 15.25		33.09 ± 9.07		< 0.00012
Comorbidities
Hypertension	751	49.77	254	8.87	< 0.0001
Hyperlipidemia	314	20.81	110	3.84	< 0.0001
Diabetes mellitus	525	34.79	174	6.08	< 0.0001
Coronary artery disease	261	17.3	69	2.41	< 0.0001
Congestive heart failure	243	16.1	39	1.36	< 0.0001
Stroke	123	8.15	37	1.29	< 0.0001
Chronic kidney disease	124	8.22	22	0.77	< 0.0001
Asthma	186	12.33	75	2.62	< 0.0001
Chronic obstructive pulmonary disease	145	9.61	34	1.19	< 0.0001
Peripheral arterial occlusive disease	29	1.92	3	0.1	< 0.0001a
Gastrointestinal ulcer	185	12.26	73	2.55	< 0.0001
Gastrointestinal bleeding	44	2.92	12	0.42	< 0.0001

¹Chi-square test.

²t test.

^aFisher’s exact test. The means (median) of follow-up period were 5.68 (5.31) years and 4.21 (3.84) years for the study bariatric surgery cohort and comparison cohorts, respectively. SD: Standard deviation.

Table 2 Cox model with hazard ratio and 95% confidence intervals of anemia associated with receiving bariatric surgery among morbidly obese patients

Variable	Anemia	Crude1			Adjusted2
	No. (n = 221)	HR	(95%CI)	P value	HR	(95%CI)	P value
Receiving bariatric surgery
No	38	1.00	reference		1.00	reference
Yes	183	1.71	(1.2-2.44)	0.003	2.36	(1.52-3.65)	0.0001
Gender
Female	186	1.00	reference		1.00	reference
Male	35	0.32	(0.22-0.46)	< 0.0001	0.33	(0.23-0.48)	< 0.0001
Age
20-29 years	88	1.00	reference		1.00	reference
30-64 years	126	1.08	(0.82-1.41)	0.6028	1.06	(0.79-1.41)	0.6956
65-100 years	7	1.33	(0.61-2.88)	0.4724	1.33	(0.54-3.3)	0.5391
Comorbidities (ref = non-)
Hypertension	41	1.07	(0.76-1.51)	0.6837	1.43	(0.9-2.27)	0.1349
Hyperlipidemia	18	1.06	(0.65-1.71)	0.8249	1.14	(0.64-2.01)	0.6595
Diabetes mellitus	26	0.95	(0.63-1.44)	0.812	0.96	(0.59-1.57)	0.8826
Coronary artery disease	15	1.23	(0.73-2.08)	0.441	1.17	(0.61-2.25)	0.6403
Congestive heart failure	10	1.02	(0.54-1.93)	0.9436	0.91	(0.42-1.94)	0.8027
Stroke	4	0.63	(0.23-1.7)	0.3611	0.52	(0.18-1.5)	0.2286
Chronic kidney disease	7	1.32	(0.62-2.8)	0.4752	1.47	(0.66-3.28)	0.3504
Asthma	17	1.74	(1.06-2.85)	0.0293	1.85	(1.05-3.25)	0.034
Chronic obstructive pulmonary disease	6	0.93	(0.41-2.08)	0.8514	0.56	(0.22-1.43)	0.2267
Peripheral arterial occlusive disease	1	0.99	(0.14-7.05)	0.9905	1.47	(0.2-10.88)	0.705
Gastrointestinal ulcer	20	2.17	(1.37-3.44)	0.001	2.25	(1.34-3.77)	0.0021
Gastrointestinal bleeding	5	2.64	(1.09-6.42)	0.0321	1.83	(0.7-4.78)	0.2204

¹Crude HR: Represented relative hazard ratio.

²Adjusted HR: Represented adjusted hazard ratio: Mutually adjusted for sex, age, receiving bariatric surgery, and baseline comorbidities (as like tables) in Cox proportional hazard regression.

Table 3 Incidence rate and hazard ratio with 95% confidence intervals of anemia associated with receiving bariatric surgery, stratified by sex and age

Variable	Receiving bariatric surgery						Receiving vs not-receiving bariatric surgery
	No			Yes			Crude HR	Adjusted HR2
	Event	Person years	IR1	Event	Person years	IR1
Total	38	6359	5.98	183	16277	11.24	1.71(1.20-2.44)b	2.36(1.52-3.65)c
Gender
Female	27	3455	7.82	159	10688	14.88	1.67(1.10-2.53)a	2.48(1.50-4.09)c
Male	11	2905	3.79	24	5588	4.29	1.24(0.60-2.55)	2.04(0.89-4.70)
Age group, yr
20-29 yr	4	1386	2.89	84	7825	10.73	3.11(1.14-8.54)a	3.83(1.13-12.99)a
30-64 yr	27	4341	6.22	99	8446	11.72	1.81(1.18-2.79)b	2.37(1.45-3.88)c
65-100 yr	7	632	11.07	0	6	0	-	-

¹IR: Incidence rates, per 1000 person-years.

²Represented adjusted hazard ratio: Mutually adjusted for sex, age, receiving bariatric surgery, and baseline comorbidities (as like tables) in Cox proportional hazard regression.

^aP < 0.05.

^bP < 0.01.

^cP < 0.001. HR: Hazard ratio.

Table 4 Cox model with hazard ratio and 95% confidence intervals of anemia associated with receiving malabsorptive procedures or restrictive procedures among morbidly obese patients

Variable	Anemia	Crude1			Adjusted2
	No. (n = 221)	HR	(95%CI)	P value	HR	(95%CI)	P value
Malabsorptive procedures
No	64	1	Reference		1	Reference
Yes	157	2.76	(2.06-3.70)	< 0.0001	3.18	(2.29-4.40)	< 0.0001
Restrictive procedures
No	62	1	Reference		1	Reference
Yes	159	1.38	(1.02-1.86)	0.0356	1.55	(1.10-2.19)	0.0129

¹Crude HR: Represented relative hazard ratio.

²Adjusted HR: Represented adjusted hazard ratio: Mutually adjusted for sex, age, receiving bariatric surgery or not, baseline comorbidities (as like tables) in Cox proportional hazard regression. CI: Confidence interval; HR: Hazard ratio.