Erythropoietin Dose and Mortality in Hemodialysis Patients: Marginal Structural Model to Examine Causality

Table 1

Patient characteristics by weekly epoetin-α dose categories.

	Total	Averaged weekly epoetin-α dose during follow-up period (U/week)
		<6 000	6 000 to <12 000	12 000 to <18 000	18 000 to <24 000	24 000 to <30 000	≥30 000
(%)	128 598 (100)	6 644 ()	23 314 ()	26 852 ()	21 487 ()	15 278 ()	35 023 ()
Age (yr)	62 ± 15	62 ± 16	63 ± 15	62 ± 15	62 ± 15	62 ± 15	60 ± 15
Female (%)	70 309 (55)	4 191 (63)	13 107 (56)	14 604 (54)	11 541 (54)	8 153 (53)	18 713 (53)
Dialysis vintage (mo)	3 (1,28)	16 (2,39)	7 (1,30)	4 (1,27)	2 (1,26)	2, (1,25)	2 (1,26)
Race (%)
Caucasian	55 107 (43)	3 181 (48)	10 057 (43)	11 026 (41)	9 072 (42)	6 460 (42)	15 311 (44)
African American	41 257 (32)	1 678 (25)	6 286 (27)	8 104 (30)	6 775 (32)	5 173 (34)	13 241 (38)
Hispanic	18 409 ()	968 ()	4 032 ()	4 384 ()	3 336 ()	2 116 ()	3 573 ()
Asian	3 887 ()	218 ()	885 ()	1 002 ()	675 ()	436 ()	671 ()
Other	9 938 ()	599 ()	2 054 ()	2 336 ()	1 629 ()	1 093 ()	2 227 ()
Insurance (%)
Medicare	81 230 (63)	4 357 (66)	14 881 (64)	17 062 (64)	13 497 (63)	9 645 (63)	21 788 (62)
Medicaid	6 777 ()	194 ()	989 ()	1 358 ()	1 225 ()	897 ()	2 114 ()
Private	12 156 ()	623 ()	2 344 ()	2 718 ()	2 138 ()	1 414 ()	2 919 ()
Other	28 435 (22)	1 470 (22)	5 100 (22)	5 714 (21)	4 627 (22)	3 322 (22)	8 202 (23)
Marital status (%)
Married	51 385 (40)	3 057 (46)	9 942 (43)	10 888 (41)	8 368 (39)	5 934 (39)	13 196 (38)
Divorced	8 725 ()	434 ()	1 462 ()	1 778 ()	1 470 ()	1 055 ()	2 526 ()
Single	29 615 (23)	1 482 (22)	4 939 (21)	5 701 (21)	4 873 (23)	3 536 (23)	9 084 (26)
Widowed	16 521 ()	823 ()	3 186 ()	3 641 ()	2 783 ()	1 990 ()	4 098 ()
Comorbidities (%)
DM	73 847 (57)	3 353 (50)	12 972 (56)	15 550 (58)	12 787 (60)	9 147 (60)	20 038 (57)
HTN	96 852 (79)	4 986 (81)	17 714 (80)	20 485 (80)	16 337 (80)	11 560 (80)	25 770 (78)
IHD	26 062 (21)	1 287 (21)	4 777 (22)	5 549 (22)	4 470 (22)	3 192 (22)	6 787 (20)
CHF	33 534 (28)	1 475 (24)	5 663 (26)	7 005 (27)	5 691 (28)	4 249 (29)	9 451 (28)
PVD	13 820 ()	669 ()	2 404 ()	2 842 ()	2 373 ()	1 770 ()	3 762 ()
CVA	9 015 ()	482 ()	1 628 ()	1 928 ()	1 632 ()	1 025 ()	2 320 ()
COPD	6 904 ()	377 ()	1 140 ()	1 365 ()	1 135 ()	887 ()	2 000 ()
Malignancy	5 538 ()	209 ()	829 ()	1 019 ()	879 ()	622 ()	1 980 ()
Current smoking	5 854 ()	345 ()	978 ()	1 134 ()	971 ()	650 ()	1 776 ()
BMI (kg/m^2)	26.6 ± 6.7	26.7 ± 6.5	26.2 ± 6.0	26.4 ± 6.4	26.7 ± 6.5	26.8 ± 6.9	27.1 ± 7.4
Laboratory parameters
Hemoglobin (g/dL)	12.1 ± 1.0	12.6 ± 0.8	12.4 ± 0.7	12.3 ± 0.8	12.2 ± 0.8	12.0 ± 0.9	11.5 ± 1.2
Creatinine (mg/dL)	8.2 ± 3.0	8.4 ± 3.2	8.4 ± 3.0	8.4 ± 3.0	8.3 ± 3.0	8.1 ± 3.0	8.0 ± 3.1
Albumin (g/dL)	3.7 ± 0.4	3.9 ± 0.3	3.9 ± 0.3	3.8 ± 0.4	3.7 ± 0.4	3.7 ± 0.4	3.5 ± 0.5
TIBC (mg/dL)	203 ± 41	215 ± 36	211 ± 36	206 ± 37	203 ± 39	201 ± 40	194 ± 46
Calcium (mg/dL)	9.3 ± 0.6	9.4 ± 0.6	9.4 ± 0.6	9.3 ± 0.6	9.3 ± 0.6	9.2 ± 0.6	9.1 ± 0.7
Phosphorus (mg/dL)	5.6 ± 1.3	5.4 ± 1.2	5.4 ± 1.1	5.5 ± 1.2	5.6 ± 1.3	5.6 ± 1.3	5.7 ± 1.4
WBC (×10^3/mm^3)	7.4 ± 2.4	7.4 ± 2.2	7.4 ± 2.0	7.4 ± 2.1	7.4 ± 2.2	7.5 ± 2.4	7.5 ± 2.9
Lymphocyte (%)	20.3 ± 7.3	22.3 ± 7.4	21.7 ± 7.2	21.0 ± 7.2	20.3 ± 7.2	19.6 ± 7.2	18.8 ± 7.4
Ferritin (ng/mL)	515 (314,742)	572 (377,777)	554 (362,755)	532 (341,741)	509 (313,728)	491 (291,730)	473 (265,737)
Single-pool	1.6 ± 0.3	1.7 ± 0.3	1.7 ± 0.3	1.6 ± 0.3	1.6 ± 0.3	1.6 ± 0.3	1.5 ± 0.3
nPNA (g/kg/day)	1.0 ± 0.2	1.0 ± 0.2	1.0 ± 0.2	1.0 ± 0.2	1.0 ± 0.2	1.0 ± 0.2	0.9 ± 0.2

Note: categorical variables are expressed as frequency (percentage). Continuous variables are given as mean ± SD or median (interquartile range) as appropriate.
Conversion factors for units: hemoglobin and albumin in g/dL to g/L ×10; creatinine in mg/dL to μmol/L ×88.4; calcium in mg/dL to mmol/L ×0.2495; and phosphorus in mg/dL to mmol/L ×0.3229. No conversion necessary for ferritin in ng/mL and μg/L and WBC count in 10³/L and 10⁹/L. DM = diabetes mellitus, HTN = hypertension, IHD = ischemic heart disease, CHF = congestive heart failure, PVD = peripheral vascular disease, CVA = cerebrovascular accident, COPD = chronic obstructive pulmonary disease, BMI = body mass index, TIBC = total iron binding capacity, WBC = white blood cell, and nPNA = normalized protein nitrogen appearance.