Finally, a total of 3761 patients with hip fractures were collected in the current study, and 2520 patients met the inclusion criteria. The ROC analysis showed the optimum cut-off value for RDW, age, time to surgery and BMI were 14.23%, 80.5 years (based on the clinical situation, we used 81 years), 7.5 days, and 22.04 kg/m2, respectively (Table 1 and Figure 1). And 1641 patients had RDW value lower than 14.23%, and 879 had above 14.23%. After PSM, 747 pairs of patients constituted the study group (Figure 2).Before PSM, femoral neck fracture (51.8 vs 42.3), intertrochanteric fracture (48.2 vs 57.7),
diabetes (26.4 vs 20.7), tumor (2.3 vs 4.0), rural (50.6 vs 57.7), time to surgery (16.8 vs 22.2), smoking (5.9 vs 4.0), age (31.7 vs 38.6), ALB (84.0 vs 91.0), GLOB (13.2 vs 15.6), WBC (35.3 vs 35), NEU (56.4 vs 49.1), LYM (0.6 vs 0.5), MON (60.9 vs 53.0), RBC (0.1 vs 0.3), HGB (26.3 vs 19.6), HCT (29.5 vs 18.7), PLT (4.0 vs 8.4), MPV (3.7 vs 3.0), PDW (10.4 vs 9.8), PTA (1.5 vs 0.2), TT (6.2 vs2.4), FIB (41.4 vs 36.2), AT III (16.9 vs 22.9), D-D (19.1 vs 73.3), FDP (86.3 vs 77.6) differed between the high RDW group and the low RDW group. The preoperative DVT incidence rate was 12.6% (Table 2).
TABLE 1: The optimal cutoff value of continuity variables was determined by ROC analysis
Variables
|
Cut-off value
|
AUC
|
95% CI
|
P value
|
RDW
|
14.23
|
0.54
|
(0.51,0.58)
|
0.018*
|
Age (year)
|
80.50
|
0.52
|
(0.48,0.55)
|
0.384
|
Time to surgery (day)
|
7.50
|
0.69
|
(0.66,0.73)
|
<0.001*
|
BMI
|
22.04
|
0.59
|
(0.56,0.62)
|
<0.001*
|
Abbreviations: RDW, red blood cell distribution width; BMI, body mass index; AUC, the area under the ROC curve; 95% CI, 95% confidence interval.
*: P<0.05, it indicates statistically significant differences.
TABLE 2: Baseline characteristics of patients with hip fracture before and after PS matching
Variables
|
Before matching (N=2,520)
|
After matching (N=1,494)
|
|
Low RDW (n=1,942)
|
High RDW (n=878)
|
SMD
|
P value
|
Low RDW (n=747)
|
High RDW (n=747)
|
SMD
|
P value
|
Fracture type (intertrochanteric)
|
791 (48.2)
|
507 (57.7)
|
0.192
|
<0.001*
|
419 (56.1)
|
412 (55.2)
|
-0.019
|
0.715
|
Hypertension
|
869 (53.0)
|
479 (54.5)
|
0.031
|
0.461
|
405 (54.2)
|
409 (54.8)
|
0.011
|
0.835
|
Diabetes
|
433 (26.4)
|
182 (20.7)
|
-0.140
|
0.002*
|
174
(23.3)
|
166 (22.2)
|
-0.026
|
0.622
|
Heart disease
|
540 (32.9)
|
287 (32.7)
|
-0.005
|
0.896
|
243 (32.5)
|
254 (34.0)
|
0.031
|
0.546
|
Tumor
|
38 (2.3)
|
35 (4.0)
|
0.085
|
0.017*
|
28
(3.7)
|
26
(3.5)
|
-0.014
|
0.782
|
Place of residence (urban)
|
811 (49.4)
|
372 (42.3)
|
-0.144
|
0.001*
|
327 (43.8)
|
330 (44.2)
|
0.008
|
0.876
|
Time to surgery (>7.5 days)
|
276 (16.8)
|
195 (22.2)
|
0.129
|
0.001*
|
162 (21.7)
|
161 (21.6)
|
-0.003
|
0.950
|
Smoking
|
97
(5.9)
|
35
(4.0)
|
-0.099
|
0.038*
|
36
(4.8)
|
33
(4.4)
|
-0.021
|
0.712
|
Gender
(male)
|
539 (32.8)
|
274 (31.2)
|
-0.036
|
0.392
|
243 (32.5)
|
234 (31.3)
|
-0.026
|
0.617
|
Age
(≥81 years)
|
520 (31.7)
|
339 (38.6)
|
0.141
|
0.001*
|
292 (39.1)
|
285 (38.2)
|
-0.019
|
0.710
|
BMI
(≥22.04 kg/m2)
|
1054 (64.2)
|
546 (62.1)
|
0.044
|
0.294
|
447 (59.8)
|
470 (62.9)
|
-0.063
|
0.222
|
ALB
(˂40 g/L)
|
1379 (84.0)
|
800 (91.0)
|
-0.244
|
<0.001*
|
675 (90.4)
|
675 (90.4)
|
0.000
|
1.000
|
GLOB
(˂20 g/L)
|
217 (13.2)
|
137 (15.6)
|
-0.082
|
0.039*
|
107 (14.3)
|
119 (15.9)
|
-0.043
|
0.687
|
WBC (>9.5⨯109/L)
|
580 (35.3)
|
308 (35.0)
|
-0.006
|
0.035*
|
277 (37.1)
|
275 (36.8)
|
-0.006
|
0.994
|
NEU (>6.3⨯109/L)
|
926 (56.4)
|
432 (49.1)
|
-0.146
|
0.001*
|
404 (54.1)
|
394 (52.7)
|
-0.027
|
0.726
|
LYM
(<1.1⨯109/L)
|
859 (52.3)
|
407 (46.3)
|
-0.023
|
0.012*
|
376 (50.3)
|
368 (49.3)
|
<0.001
|
0.917
|
MON (>0.6⨯109/L)
|
999 (60.9)
|
466 (53.0)
|
-0.157
|
0.001*
|
418 (56.0)
|
418 (56.0)
|
<0.001
|
1.000
|
RBC
(< lower limit)
|
1135 (69.2)
|
680 (77.4)
|
0.038
|
<0.001*
|
574 (76.8)
|
570 (76.3)
|
0.886
|
0.886
|
HGB
(˂ lower limit)
|
431 (26.3)
|
172 (19.6)
|
0.159
|
<0.001*
|
590 (79.0)
|
589 (78.8)
|
-0.003
|
0.710
|
HCT
(˂ lower limit)
|
484 (29.5)
|
164 (18.7)
|
0.270
|
<0.001*
|
597 (79.9)
|
591 (79.1)
|
-0.020
|
0.854
|
PLT
(> higher limit)
|
65
(4.0)
|
74
(8.4)
|
0.160
|
<0.001*
|
47
(6.3)
|
49
(6.6)
|
0.010
|
0.687
|
MPV (>11.0 f L)
|
61 (3.7)
|
26 (3.0)
|
-0.045
|
<0.001*
|
25 (3.3)
|
24 (3.2)
|
-0.008
|
0.982
|
PDW (>18.1 %)
|
22 (1.3)
|
27 (3.1)
|
0.100
|
<0.001*
|
16 (2.1)
|
16 (2.1)
|
<0.001
|
0.694
|
PT
(˂ lower limit)
|
24
(1.5)
|
7
(0.8)
|
-0.076
|
0.148
|
7
(0.9)
|
6
(0.8)
|
-0.015
|
0.781
|
PTA
(> higher limit)
|
24
(1.5)
|
2
(0.2)
|
-0.259
|
0.008*
|
6
(0.8)
|
2
(0.3)
|
-0.112
|
0.325
|
APTT
(˂ lower limit)
|
527 (32.1)
|
3.1 (34.2)
|
-0.042
|
0.278
|
254 (34.0)
|
248 (33.2)
|
0.014
|
0.742
|
TT
(>higher limit)
|
102
(6.2)
|
21
(2.4)
|
-0.250
|
<0.001*
|
25
(3.3)
|
20
(2.7)
|
-0.044
|
0.698
|
FIB
(>higher limit)
|
679 (41.4)
|
318 (36.2)
|
0.114
|
0.026*
|
301 (40.3)
|
291 (39.0)
|
0.039
|
0.589
|
AT III
(˂ lower limit)
|
2788 (16.9)
|
201 (22.9)
|
0.141
|
<0.001*
|
164 (22.0)
|
160 (21.4)
|
-0.013
|
0.932
|
D-D
(>0.5 mg/L)
|
1327 (19.1)
|
644 (73.3)
|
0.172
|
<0.001*
|
578 (77.4)
|
583 (78.0)
|
-0.015
|
0.756
|
FDP
(>5 mg/L)
|
1416 (86.3)
|
682 (77.6)
|
0.209
|
<0.001*
|
618 (82.7)
|
612 (81.9)
|
0.019
|
0.684
|
Abbreviations: RDW, red blood cell distribution width; SMD, standardized mean deviations; BMI, body mass index; ALB, albumin; GLOB, globulin; WBC, white blood cell; NEU, neutrophil; LYM, lymphocyte; MON, monocyte count; RBC, red blood cell; HGB, hemoglobin; HCT, hematocrit; PLT, blood platelet; MPV, mean platelet volume; PDW, platelet distribution width; PT, prothrombin time; PTA, prothrombin activity; APTT, partial thromboplastin time; TT, thrombin time; FIB, fibrinogen; AT III, anti-thrombase III; D-D, D-Dimer; FDP, fibrinogen degradation product.
*: P<0.05, it indicates statistically significant differences.
After PSM, 747 pairs of patients were identified. The SMD of all included covariates which ranged from -0.063 to 0.039 were less than 0.10 and indicated that the groups were relatively well matched. There were no statistically significant differences in all covariates between the high RDW group and the low RDW group (P>0.05) (Table 2).
The result of conditional logistic regression analyses revealed no significant association of factors with preoperative DVT, except RDW (P=0.001; 95% CI, 1.28 to 2.62), fracture type (P=0.003; 95% CI, 0.20 to 0.72), BMI (P=0.002; 95% CI, 1.39 to 4.18), and time to surgery (P<0.001; 95% CI, 1.89 to 7.35) (Table 3). And both before and after PSM, there existed a correlative relationship between RDW and preoperative DVT in elderly patients with hip fractures. RDW was associated with 1.83-fold increased risk (adjusted RR, 1.83; 95% CI, 1.28 to 2.62) of preoperative DVT, and it showed the 1.28-fold increased risk in raw data (crude RR, 1.28; 95% CI, 1.15 to 1.43) and 0.78-fold increased risk in the unadjusted data (RR, 0.78; 95% CI, 0.70 to 0.88). The preoperative DVT incidence rate was 15.53% (Table 4).
TABLE 3: Risk for preoperative DVT
Variables
|
RR
|
95% CI
|
P value
|
RDW
|
1.83
|
1.28-2.62
|
0.001*
|
Fracture type (intertrochanteric)
|
2.65
|
1.40-5.04
|
0.003*
|
Hypertension
|
0.94
|
0.56-1.56
|
0.802
|
Diabetes
|
1.36
|
0.69-2.66
|
0.376
|
Heart disease
|
0.92
|
0.52-1.61
|
0.761
|
Tumor
|
1.19
|
0.30-4.63
|
0.807
|
Place of residence
(urban)
|
1.70
|
0.97-2.98
|
0.064
|
Time to surgery
(>7.5 days)
|
3.73
|
1.89-7.35
|
<0.001*
|
Smoking
|
3.11
|
0.81-11.92
|
0.099
|
Gender (male)
|
0.59
|
0.30-1.15
|
0.120
|
Age (≥81 years)
|
0.94
|
0.53-1.68
|
0.839
|
BMI (≥22.04 kg/m2)
|
2.41
|
1.39-4.18
|
0.002*
|
ALB (˂40 g/L)
|
1.38
|
0.45-4.25
|
0.573
|
GLOB (˂20 g/L)
|
0.76
|
0.39-1.46
|
0.401
|
WBC (>9.5⨯109/L)
|
0.85
|
0.55-1.32
|
0.479
|
NEU (>6.3⨯109/L)
|
0.99
|
0.66-1.48
|
0.954
|
LYM (˂1.1⨯109/L)
|
0.98
|
0.58-1.66
|
0.947
|
MON (>0.6⨯109/L)
|
1.05
|
0.73-1.50
|
0.798
|
RBC (˂ lower limit)
|
0.64
|
0.27-1.51
|
0.312
|
HGB (˂ lower limit)
|
0.92
|
0.40-2.10
|
0.845
|
HCT (˂ lower limit)
|
0.77
|
0.31-1.91
|
0.575
|
PLT (> higher limit)
|
1.19
|
0.71-2.00
|
0.507
|
MPV (>11.0 f L)
|
0.81
|
0.36-1.82
|
0.602
|
PDW (>18.1 %)
|
0.74
|
0.36-1.53
|
0.419
|
PT (˂ lower limit)
|
0.75
|
0.46-1.24
|
0.265
|
PTA (> higher limit)
|
0.85
|
0.33-2.20
|
0.742
|
APTT (˂ lower limit)
|
1.36
|
0.85-2.19
|
0.203
|
TT (> higher limit)
|
1.14
|
0.66-1.97
|
0.644
|
FIB (> higher limit)
|
1.01
|
0.76-1.34
|
0.949
|
AT III (˂ lower limit)
|
0.83
|
0.51-1.37
|
0.466
|
D-D (>0.5 mg./L)
|
1.03
|
0.45-2.16
|
0.938
|
FDP (>5 mg/L)
|
1.49
|
0.70-3.20
|
0.302
|
Abbreviations: RR, relative ratio; 95% CI, 95% confidence interval; RDW, red blood cell distribution width; BMI, body mass index; ALB, albumin; GLOB, globulin; WBC, white blood cell; NEU, neutrophil; LYM, lymphocyte; MON, monocyte count; RBC, red blood cell; HGB, hemoglobin; HCT, hematocrit; PLT, blood platelet; MPV, mean platelet volume; PDW, platelet distribution width; PT, prothrombin time; PTA, prothrombin activity; APTT, partial thromboplastin time; TT, thrombin time; FIB, fibrinogen; AT III, anti-thrombase III; D-D, D-Dimer; FDP, fibrinogen degradation product.
*: P<0.05, it indicates statistically significant differences.
TABLE 4: Comparison of the RR Value in Different Settings
Outcome
|
Preoperative
RDW (%)
|
Crude
|
PSM
|
Event/N
|
RR
(95% CI)
|
P
|
Event/N
|
Before Adjusted
|
After Adjusted
|
RR
(95% CI)
|
P
|
RR
(95% CI)
|
P
|
RDW
|
˂14.23
≥14.23
|
150/1641
168/879
|
1.28
(1.15-1.43)
|
<0.001*
|
90/747
142/747
|
1.58
(1.24-2.01)
|
<0.001*
|
1.83
(1.28-2.62)
|
<0.001*
|
Abbreviations: RR, relative ratio; 95% CI, 95% confidence interval; PSM, propensity score matching.
*: P<0.05, it indicates statistically significant differences.