Clinical Factors Associated with Positive Active Bleeder CT Angiography in the Emergency Setting

Author

Lu Mao

Statistical analysis

Categorical variables are summarized by n (%) and continuous variables by median (inter-quartile range, IQR). The chi-square test is used to compare categorical variables and the Wilcoxon rank-sum test for continuous variables. The predictive value of CT imaging against gold standard is assessed by sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic odds ratio (DOR) with 95% confidence intervals (CI). The association between clinical factors and CT positivity is evaluated by univariate and multiple logistic regression models. The receiver operating characteristic (ROC) curve is plotted to assess the predictive performance of the logistic model. Imaging statistics are compared by median (IQR) and Wilcoxon signed-rank test.

Characteristics by CT imaging result

Patient demographics and clinical variables are summarized by CT imaging result for bleeding status in Table 1 below. Quantitative variables are summarized by median (inter-quartile range, IQR) and categorical variables by n (%).

Table 1: Patient characteristics by CT imaging for bleeding status.
Characteristic CT-Negative, N = 2631 CT-Positive, N = 561 p-value2
Age at time of exam 62 (49, 74) 67 (53, 73) 0.4
Gender

0.7
    Female 124 (47%) 25 (45%)
    Male 139 (53%) 31 (55%)
Race

0.11
    White 237 (90%) 52 (93%)
    Black/African American 13 (4.9%) 0 (0%)
    Asian/Pacific Islander 8 (3.0%) 4 (7.1%)
    Other/Unknown 5 (1.9%) 0 (0%)
BMI 27 (23, 32) 28 (24, 33) 0.4
Disposition

<0.001
    Admitted (incl. ICU) 180 (68%) 55 (98%)
    Discharged/Home 76 (29%) 1 (1.8%)
    Hospice/Assisted Living 3 (1.1%) 0 (0%)
    Deceased 2 (0.8%) 0 (0%)
    Inpatient 2 (0.8%) 0 (0%)
Endoscopy Positive 14 (5.3%) 9 (16%) 0.009
IR Positive 8 (3.0%) 19 (34%) <0.001
Surgery Positive 0 (0%) 1 (1.8%) 0.2
Systolic BP 130 (114, 147) 117 (101, 138) 0.014
Diastolic BP 74 (64, 82) 66 (56, 78) 0.008
Heart Rate 85 (74, 98) 83 (72, 96) 0.5
Respiratory Rate 18.0 (16.0, 20.0) 18.0 (16.0, 19.0) 0.2
Oxygen Saturation 97.00 (95.00, 99.00) 98.00 (96.00, 99.00) 0.024
Cancer 69 (26%) 14 (25%) 0.8
Hypertension 126 (48%) 32 (57%) 0.2
Diabetes 58 (22%) 11 (20%) 0.7
Coronary Artery Disease 35 (13%) 15 (27%) 0.012
Peptic Ulcer Disease 3 (1.1%) 3 (5.4%) 0.069
Alcohol Abuse 29 (11%) 4 (7.1%) 0.4
Chronic Livear Disease 24 (9.1%) 4 (7.1%) 0.8
Portal HTN (varices) 16 (6.1%) 3 (5.4%) >0.9
Diverticulosis 16 (6.1%) 8 (14%) 0.048
End Stage Liver Disease 8 (3.0%) 1 (1.8%) >0.9
H. Pylori 2 (0.8%) 1 (1.8%) 0.4
Abd surgery within 3 months 43 (16%) 15 (27%) 0.066
Hb (g/dL) (record all prior to CT) 11.10 (8.50, 13.40) 10.50 (7.80, 12.70) 0.2
Hct (g/dL) (record all prior to CT) 34 (26, 41) 32 (27, 39) 0.3
Platelets 252 (191, 332) 251 (193, 319) 0.7
BUN 17 (13, 27) 20 (14, 31) 0.13
Creatinine 0.90 (0.71, 1.13) 0.97 (0.81, 1.22) 0.061
Glucose 115 (100, 140) 129 (108, 162) 0.021
AST 22 (16, 34) 23 (16, 45) 0.4
ALT 20 (13, 33) 24 (15, 41) 0.3
aPTT 31 (26, 35) 29 (26, 36) 0.7
INR 1.20 (1.00, 1.40) 1.20 (1.00, 1.60) 0.4
Anticoagulation 58 (22%) 11 (20%) 0.7
Antiplatelets 45 (17%) 15 (27%) 0.093
SSRI 32 (12%) 10 (18%) 0.3
Steroids 22 (8.4%) 7 (13%) 0.3
Any Medication 128 (49%) 30 (54%) 0.5
1 Median (IQR); n (%)
2 Wilcoxon rank sum test; Pearson’s Chi-squared test; Fisher’s exact test

Predictive value of CT imaging against gold standard

Gold standard for active bleeding status is defined as either endoscopy, interventional radiology (IR), or surgery positive (see Table 1). A cross-tabulation between the imaging result and gold standard is shown in Table 2 below.

Table 2: Cross-tabulation of CT imaging result and gold standard.
Gold standard Total p-value1
Negative Positive
CT Result


<0.001
    CT-Negative 242 (76%) 21 (6.6%) 263 (82%)
    CT-Positive 28 (8.8%) 28 (8.8%) 56 (18%)
Total 270 (85%) 49 (15%) 319 (100%)
1 Pearson’s Chi-squared test

Diagnostic metrics, such as sensitivity, specificity, positive predictive value (PPV), negative predictive value, and diagnostic odds ratio (DOR), along with their 95% confidence intervals (CI) are shown below.

Table 3: Diagnostic metrics of CT imaging against gold standard for bleeding status.
Metric Estimate 95% CI
Sensitivity 0.571 0.433, 0.7
Specificity 0.896 0.854, 0.927
PPV 0.5 0.373, 0.627
NPV 0.92 0.881, 0.947
DOR 11.5 5.8, 22.9

Factors associated with CT positive

A set of factors are picked from Table 1 based on their strength of asssociation with CT positivity.

Univariate analysis

First, a univariate logistic regression model is built for each factor to assess its association with CT result. The univariate odds ratios (OR; for CT positivity) are summarized in Table 4 below.

Table 4: Univariate logistic regression analysis of CT positivity against clinical factors.
Characteristic OR1 95% CI1 p-value
Discharged

<0.001
    No 1.00 —
    Yes 0.04 0.00, 0.21
Systolic BP 0.99 0.97, 1.00 0.017
Diastolic BP 0.97 0.95, 0.99 0.006
Oxygen Saturation 1.14 1.01, 1.30 0.032
Coronary Artery Disease

0.017
    No 1.00 —
    Yes 2.38 1.17, 4.70
Diverticulosis

0.051
    No 1.00 —
    Yes 2.57 1.00, 6.20
Abd surgery within 3 months

0.077
    No 1.00 —
    Yes 1.87 0.93, 3.63
BUN 1.01 0.99, 1.02 0.31
Creatinine 1.10 0.99, 1.52 0.052
Glucose 1.00 1.00, 1.01 0.34
1 OR = Odds Ratio, CI = Confidence Interval

Multiple logistic regression

A multiple logistic regression model is fit below to evaluate each factor’s independent contribution to predicting CT positivity in the presence of others. Oxygen saturation and diverticulosis are two strongest independent predictors of a positive outcome.

Table 5: Multiple logistic regression analysis of CT positivity against clinical factors.
Characteristic OR1 95% CI1 p-value
Discharged


    No — —
    Yes 0.00
0.2
Systolic BP 1.00 0.98, 1.02 >0.9
Diastolic BP 0.98 0.94, 1.01 0.2
Oxygen Saturation 1.19 1.05, 1.37 0.011
Coronary Artery Disease


    No — —
    Yes 2.00 0.81, 4.83 0.12
Diverticulosis


    No — —
    Yes 4.48 1.51, 13.2 0.006
Abd surgery within 3 months


    No — —
    Yes 2.11 0.96, 4.58 0.059
BUN 0.99 0.97, 1.01 0.4
Creatinine 1.15 1.04, 1.64 0.14
Glucose 1.00 1.00, 1.01 0.2
1 OR = Odds Ratio, CI = Confidence Interval

The receiver operating characteristic (ROC) curve (by 10-fold cross-validation) of the logistic model in Table 5 for predicting CT positivity is plotted below.

Comparison of imaging statistics

Table 6: Comparison of imaging statistics by median (IQR) and Wilcoxon signed-rank test.
# Images Total Exam (No Thins) # Images Venous Exam (No Thins) p-value
1454 (1339.5, 1591.5) 554 (509.5, 606) <0.001
# Images Total Exam (With Thins) # Images Venous Exam (No Thins) p-value
5643 (5214.5, 6108) 554 (509.5, 606) <0.001
CTDIvol Total Exam CTDIvol Venous Series p-value
53 (36.6, 72.2) 16.2 (11.1, 23.1) <0.001
DLP Total Exam DLP Venous Series p-value
2687.7 (1823.6, 3834.6) 845.5 (555.6, 1233.3) <0.001