Prognostic Value of Hemoglobin Concentration on Renal Outcomes with Diabetic Kidney Disease: A Retrospective Cohort Study

Figures & data

Figure 1 Study design and flowchart of study participants.

Table 1 Baseline Characteristics of All the Patients at Enrollment (n=815)

Hb Quartiles	Q1 (56–104g/L)	Q2 (105–120g/L)	Q3 (121–137g/L)	Q4 (138–187g/L)	P-value
Participants	204	195	203	213
SBP (mmHg)	149.734 ± 22.865	148.030 ± 21.677	142.886 ± 22.706	143.364 ± 22.497	0.003
DBP (mmHg)	80.241 ± 12.718	83.365 ± 12.244	81.821 ± 12.546	86.704 ± 14.199	<0.001
BMI (kg/m^2)	23.962 ± 3.630	25.185 ± 3.553	25.758 ± 3.640	25.986 ± 3.943	<0.001
Age (years)	55.711 ± 9.945	56.682 ± 9.800	58.463 ± 8.834	55.150 ± 10.728	0.004
WBC (*10^9/L)	7.633 ± 2.136	7.859 ± 2.152	7.896 ± 2.161	7.470 ± 1.773	0.119
BUN (mmol/L)	12.677 ± 5.706	10.056 ± 4.467	7.790 ± 3.078	6.503 ± 2.368	<0.001
UA (μmol/L)	438.414 ± 119.760	424.422 ± 118.138	412.553 ± 124.423	406.382 ± 108.543	0.031
Cys C (mg/L)	2.256 ± 0.949	1.845 ± 0.764	1.575 ± 0.715	1.284 ± 0.619	<0.001
CHOL (mmol/L)	5.433 ± 2.073	5.700 ± 2.067	5.641 ± 1.957	5.176 ± 1.734	0.029
LDL-C (mmol/L)	3.325 ± 1.429	3.594 ± 1.469	3.391 ± 1.310	3.184 ± 1.047	0.018
HDL-C (mmol/L)	1.164 ± 0.402	1.124 ± 0.333	1.167 ± 0.333	1.054 ± 0.302	0.002
TG (mmol/L)	1.745 (1.110–2.662)	1.940 (1.315–2.865)	1.800 (1.200–3.035)	1.990 (1.360–3.100)	0.044
ALT (U/L)	19.823 (13.000–29.459)	22.843 (16.996) 18.000 (12.149–27.718)	18.281 (14.000–28.000)	23.000 (16.229–34.000)	<0.001
AST (U/L)	20.974 (14.369–26.763)	19.000 (14.000–26.131)	19.000 (14.980–25.000)	20.468 (16.681–30.609)	0.006
TP (g/L)	61.192 ± 10.050	66.383 ± 8.967	67.487 ± 9.132	69.409 ± 7.145	<0.001
ALB (g/L)	31.073 ± 6.926	35.423 ± 6.536	36.711 ± 6.701	39.792 ± 5.101	<0.001
K (mmol/L)	4.186 ± 0.621	4.143 ± 0.600	3.991 ± 0.524	3.927 ± 0.490	<0.001
MG (mmol/L)	0.861 ± 0.112	0.843 ± 0.115	0.844 ± 0.122	0.837 ± 0.124	0.202
Ca (mmol/L)	2.180 ± 0.195	2.274 ± 0.153	2.291 ± 0.146	2.330 ± 0.117	<0.001
P (mmol/L)	1.420 ± 0.297	1.303 ± 0.224	1.206 ± 0.201	1.184 ± 0.206	<0.001
HbA1c (%)	7.684 ± 1.804	8.183 ± 2.223	8.650 ± 2.450	8.723 ± 2.154	<0.001
Hb (g/L)	91.747 ± 9.660	113.412 ± 4.642	129.148 ± 5.135	150.192 ± 9.735	<0.001
SCr (μmol/L)	181.691 ± 76.955	148.128 ± 72.286	116.516 ± 59.612	100.538 ± 44.273	<0.001
eGFR (mL/min per 1.73 m^2)	40.494 ± 23.267	51.679 ± 27.822	64.926 ± 28.116	78.554 ± 26.907	<0.001
Gender					<0.001
Male	121 (59.314%)	107 (54.872%)	119 (58.621%)	186 (87.324%)
Female	83 (40.686%)	88 (45.128%)	84 (41.379%)	27 (12.676%)
24hU-pro	3109.665 (1199.253–5435.745)	1487.041 (449.555–4744.710)	618.860 (182.663–2847.709)	273.773 (124.044–651.340)	<0.001
24hU-alb	1862.170 (657.950–3344.025)	890.900 (163.355–2549.350)	289.800 (61.368–1772.710)	88.400 (23.200–358.800)	<0.001
Renal biopsy					<0.001
No	134 (65.686%)	158 (81.026%)	173 (85.222%)	198 (92.958%)
Yes	70 (34.314%)	37 (18.974%)	30 (14.778%)	15 (7.042%)

Notes: Continuous variables were summarized as mean (SD) or medians (quartile interval); categorical variables were displayed as percentage (%).

Abbreviations: BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; TC, total cholesterol; TG, triglyceride; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipid cholesterol; ALT, alanine aminotransferase; AST, aspartate aminotransferase; BUN, blood urea nitrogen; Scr, serum creatinine; UA, uric acid; Cys C, Cystatin C; WBC, white blood cell; TP, total protein; ALB, albumin; K, serum potassium; MG, serum magnesium; Ca, serum calcium; P, serum phosphorus; HbA1c, glycosylated hemoglobin; 24hU-pro, 24-hour urine albumin; 24hU-alb, 24 -hour urine protein.

Figure 2 Showed the distribution of Hb levels. It showed a normal distribution within a range from 56g/L to 187g/L (with an average of 121.5g/L).

Table 2 Incident Rate of Renal Composite Endpoint

Hb	Participants(n)	Renal Composite Endpoint Events(n)	Incidence Rate (95% CI)(%)	Cumulative Incidence (Per 100 Person-Year)
Total	815	182	22.331 (19.466–25.197)	12.875
Q1 (<104g/L)	204	82	40.196 (33.411–46.981)	32.875
Q2 (105–120g/L)	195	54	27.692 (21.356–34.029)	18.840
Q3 (121–137g/L)	203	35	17.241 (12.001–22.482)	7.978
Q4 (≥138g/L)	213	11	5.164 (2.168–8.160)	2.506
P for trend			<0.0001

Figure 3 The distribution of different eGFR levels and 24hU-alb severity levels with different hemoglobin levels. (A) The relationship between eGFR and Hb in male DKD patients. (B) The relationship between eGFR and Hb in female DKD patients. (C) The relationship between 24hU-alb and Hb in male DKD patients. (D) The relationship between 24hU-alb and Hb in female DKD patients.

Figure 4 Incidence of renal composite endpoint according to Hb quartiles. This figure showed that participants within the highest Hb group had lower incidence rate of renal composite endpoint compared to the group with the lowest Hb (p < 0.0001 for trend).

Table 3 The Results of Univariate Analysis of Renal Composite Endpoint

Variable	Statistics	HR (95% CI)	P value
SBP (mmHg)	146.668 ± 22.742	1.015 (1.008, 1.022)	<0.00001
DBP (mmHg)	83.405 ± 13.307	1.004 (0.993, 1.015)	0.46333
BMI (kg/m^2)	25.310 ± 3.357	0.900 (0.859, 0.943)	0.00001
SEX
Male	534 (65.441%)	1.0
Female	282 (34.559%)	0.747 (0.547, 1.021)	0.06722
Age (years)	56.461 ± 9.937	0.973 (0.959, 0.987)	0.00015
Hb (g/L)	121.527 ± 22.947	0.961 (0.955, 0.968)	<0.00001
24hUP	2461.425 ± 3241.219	1.000 (1.000, 1.000)	<0.00001
24hUAlb	1390.625 ± 1833.980	1.000 (1.000, 1.000)	<0.00001
SCr (μmol/L)	136.146 ± 71.376	1.013 (1.012, 1.015)	<0.00001
BUN (mmol/L)	9.215 ± 4.725	1.141 (1.114, 1.168)	<0.00001
UA (μmol/L)	425.199 ± 116.725	1.001 (1.000, 1.003)	0.02042
eGFR (mL/min per 1.73 m^2)	59.255 ± 30.212	0.963 (0.956, 0.970)	<0.00001
K (mmol/L)	4.040 ± 0.561	1.615 (1.246, 2.093)	0.00029
Ca (mmol/L)	2.269 ± 0.163	0.014 (0.007, 0.028)	<0.00001
P (mmol/L)	1.280 ± 0.245	3.856 (2.355, 6.314)	<0.00001
MG (mmol/L)	0.847 ± 0.131	5.867 (1.882, 18.292)	0.00229
HbA1c (%)	8.359 ± 2.224	0.894 (0.834, 0.959)	0.00162
Cys C (mg/L)	1.583 ± 0.772	2.898 (2.421, 3.468)	<0.00001
WBC (*10^9/L)	7.526 ± 2.078	1.018 (0.950, 1.091)	0.61731
TC (mmol/L)	5.446 ± 1.923	1.119 (1.061, 1.181)	0.00004
TG (mmol/L)	2.370 ± 1.908	1.002 (0.940, 1.067)	0.95493
LDL-C (mmol/L)	3.368 ± 1.310	1.281 (1.165, 1.408)	<0.00001
AST (U/L)	23.766 ± 14.275	0.997 (0.987, 1.007)	0.57404
ALT (U/L)	25.721 ± 24.524	0.998 (0.992, 1.004)	0.48887
ALB (g/L)	35.971 ± 6.886	0.883 (0.866, 0.900)	<0.00001
HDL-C (mmol/L)	1.130 ± 0.347	1.587 (1.063, 2.368)	0.02378

Notes: Continuous variables were summarized as mean (SD) or medians (quartile interval); categorical variables were displayed as percentage (%).

Abbreviations: BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; TC, total cholesterol; TG, triglyceride; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipid cholesterol; ALT, alanine aminotransferase; AST, aspartate aminotransferase; BUN, blood urea nitrogen; Scr, serum creatinine; UA, uric acid; Cys C, Cystatin C; WBC, white blood cell; ALB, albumin; K, serum potassium; MG, serum magnesium; Ca, serum calcium; P, serum phosphorus; HbA1c, glycosylated hemoglobin; 24hU-pro, 24-hour urine albumin; 24hU-alb, 24 -hour urine protein.

Figure 5 Kaplan–Meier survival curve. The probability of renal composite endpoint-free survival differed significantly between the Hb quartiles (Log rank test, p < 0.001). The probability of renal composite endpoint-free survival gradually decreased with decreasing Hb, suggesting that the group with the highest Hb had the highest probability of renal composite endpoint-free survival.

Table 4 Relationship Between Hb and Renal Composite Events in Different Models

Exposure	Crude Model (HR, 95% CI, P)	Model I (HR, 95% CI, P)	Model II (HR, 95% CI, P)	Model III (HR, 95% CI, P)
Hb	0.960 (0.954, 0.967) <0.00001	0.959 (0.952, 0.966) <0.00001	0.975 (0.966, 0.984) <0.00001	0.973 (0.962, 0.984) <0.00001
Anemia
No	1.0	1.0	1.0	1.0
Yes	6.698 (4.537, 9.887) <0.00001	6.527 (4.336, 9.825) <0.00001	2.592 (1.622, 4.140) 0.00007	2.781 (1.626, 4.756) 0.00019
Hb Quartile
Q1	1.0	1.0	1.0	1.0
Q2	0.562 (0.398, 0.794) 0.00106	0.580 (0.408, 0.824) 0.00234	0.875 (0.587, 1.304) 0.51189	0.856 (0.523, 1.400) 0.53472
Q3	0.208 (0.139, 0.312) <0.00001	0.237 (0.156, 0.361) <0.00001	0.505 (0.315, 0.810) 0.00458	0.467 (0.265, 0.821) 0.00820
Q4	0.064 (0.034, 0.121) <0.00001	0.043 (0.022, 0.087) <0.00001	0.141 (0.064, 0.312) <0.00001	0.118 (0.045, 0.307) 0.00001
P for trend	<0.00001	<0.00001	<0.00001	0.00001

Notes: Crude model adjust for: None. Model I adjust for: SBP; DBP; BMI; Gender; Age. Model II adjust for: SBP; DBP; BMI; Gender; Age; BUN; UA; Cys C; TC; LDL-C; HDL-C; TP; ALB; ALT; K; CA; P; HbA1C; 24hUP; 24hUalb. Model III adjust for: SBP (Smooth); DBP (Smooth); BMI (Smooth); Gender; Age (Smooth); BUN (Smooth); UA (Smooth); Cys C (Smooth); TC (Smooth); LDL-C (Smooth); HDL-C (Smooth); TP (Smooth); ALB (Smooth); ALT (Smooth); K (Smooth); Ca (Smooth); P (Smooth); HbA1C (Smooth); 24hU-pro (Smooth); 24hU-alb (Smooth). Restricted cubic spline were applied.

Table 5 The Results of Two-Piecewise Regression Linear Model

Incidence of Normalization of Blood Glucose	HR, 95% CI	P
Fitting model by standard Cox regression	0.976 (0.967, 0.985)	<0.0001
Fitting model by two-piecewise Cox regression
Inflection points of Hb
< 109	1.008 (0.990, 1.026)	0.3782
> 109	0.946 (0.929, 0.962)	<0.0001
P for log-likelihood ratio test		<0.0001

Notes: We adjusted SBP; DBP; BMI; Gender; Age; BUN; UA; Cys C; TC; LDL-C; HDL-C; ALB; ALT; AST; K; Ca; P; HbA1C; 24hU-pro; 24hU-alb.

Figure 6 The non-linear relationship between Hb and the renal composite endpoint among DKD patients. We used a Cox proportional hazards regression model with cubic spline functions to evaluate the relationship between Hb and renal composite endpoint. The result showed that the relationship between Hb and renal composite endpoint was non-linear, with the inflection point of Hb being 109g/L.

Table 6 Results of Subgroup Analysis and Interaction Analysis

Subgroup	Endpoints-Free	Endpoints		HR (95% CI)	P	P for Interact
All patients	633	182
Gender						0.0267
Male	409	124	0.975 (0.965, 0.984)	0.975 (0.965, 0.984)	<0.0001
Female	224	58	1.000 (0.979, 1.022)	1.000 (0.979, 1.022)	0.9876
Age						0.2204
<60	358	118	0.976 (0.966, 0.987)	0.976 (0.966, 0.987)	<0.0001
≥60	275	64	0.987 (0.972, 1.003)	0.987 (0.972, 1.003)	0.1059
SBP						0.1721
<140	275	54	0.971 (0.956, 0.987)	0.971 (0.956, 0.987)	0.0003
≥140	358	128	0.984 (0.973, 0.995)	0.984 (0.973, 0.995)	0.0041
DBP						0.4057
<90	427	124	0.984 (0.974, 0.994)	0.984 (0.974, 0.994)	0.0024
≥90	206	58	0.976 (0.960, 0.993)	0.976 (0.960, 0.993)	0.0049
BMI						0.1258
<25	302	103	0.987 (0.975, 0.999)	0.983 (0.971, 0.996)	0.03140
≥25	331	79	0.974 (0.961, 0.987)	0.980 (0.968, 0.992)	<0.0001
UA						0.9824
<420	339	85	0.981 (0.969, 0.993)	0.981 (0.969, 0.993)	0.0021
≥420	294	97	0.981 (0.969, 0.993)	0.981 (0.969, 0.993)	0.0022
ALB						0.0842
<30	83	79	0.988 (0.975, 1.002)	0.988 (0.975, 1.002)	0.0993
>30	550	103	0.973 (0.962, 0.985)	0.973 (0.962, 0.985)	<0.0001

Notes: The model above is adjusted for SBP, DBP, Gender, Age, BUN, UA, Cys C, TC, LDL-C, HDL-C, ALB, ALT, AST, K, Ca, P, HbA1C, 24hU-pro, 24hU-alb, eGFR, but not adjusted for stratification variables.

Data Sharing Statement

The original contributions presented in the study are included in the article/Figures Material. Further inquiries can be directed to the corresponding author.