Increased Use of CT-Pulmonary Angiography Is Not Justified
Increased Use of CT-Pulmonary Angiography Is Not Justified
Over the study period (2000 to 2010), there was a 27-fold increase in the total number of CTPA (Figure 1) without a corresponding increase in yield. The total number of CTPA in the three index years 2000, 2005 and 2008 were 84, 1114 and 2287 respectively. While the number of CTPA ordered increased in all departments, the ED had the largest increase. The numbers of scans performed in the ED per 100 visits were 0.14 in 2000, 1.82 in 2005 and 2.58 in 2008. The ED also had the steepest decline in the percentage of scans positive for PE (Figure 2).
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Figure 1.
The number of CTPA performed per calendar year from 2000 to 2011. The dark bars and percentages are the CTPA that were positive for PE.
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Figure 2.
Number of CTPA by hospital department for the index years 2000, 2005 and 2008. The largest increase occurred in the emergency department (ED) which also had the steepest decline in positive yield (% above bars).
We assessed whether the use of CTPA is justified in those with low or intermediate pre-test probability by the finding of an alternative diagnosis that might explain the patient's symptoms. The frequency of alternate diagnoses found on CTPA was as follows: ED: 10%, Medicine: 5%, Surgery: 3%; p = 0.08. When we examine the data more closely, only 3.2% of potentially avoidable CTPA (low or intermediate pre-test probability and negative D-dimer) had an alternative diagnosis that was neither previously known nor evident on a chest radiograph performed prior to the CTPA.
13% of the patients did not have a prior chest X-ray defined as within 48 hours of CTPA. Among those who did undergo a chest X-ray, the findings were as follows: 40% normal, 14% pleural effusion, 11% pulmonary edema, 6% atelectasis, 6% infiltrate, and 10% other.
In contrast to 2000 and 2005, those undergoing CTPA in 2008 were significantly younger and less acutely ill as evidenced by their higher oxygen saturation and lower respiratory rate (Table 1). Moreover, patients in 2008 were much less likely to have any risk factors for thrombosis or a prior history of venous thromboembolism. There was an increase in the use of CTPA in patients with chest pain, and for "other" indications (Table 1). The increase in number of scans ordered was accompanied by a significant drop in the diagnosis of PE from 22.6% in 2000 to 13% in 2010. We also noted a change in the size and location of pulmonary emboli detected over time: in 2008, a greater proportion of PE was found distal to the lobar arteries in the segmental or sub segmental branches (Table 2). Since younger patients and women may be more at risk from the potential carcinogenic effects of ionizing radiation, we also examined age and gender in our sample. The number of CTPA performed on women under the age of 40 years increased significantly over the study period (Table 1). While 11.8% of all CTPAs performed were on women less than 40 years of age, the presence of a PE in this cohort was lower than in all CTPAs reviewed (9.1% versus 17.7%).
Across all years, physicians ordering CTPA rarely documented the pre-test probability of PE in the patients' medical records (Table 3). Our calculation of pre-test probability based on the RGS showed that more patients with low pre-test probability of PE underwent CTPA in later years (Table 3). Overall, PE was present on CTPA in 9.3% of patients with a low pre-test probability, 20.9% patients with an intermediate pre-test probability and 29.6% with a high pre-test probability of PE. Slightly over one fifth (22.2%) of patients with a high pre-test probability of PE received any form of anticoagulation prior to undergoing CTPA.
D-dimer was assessed in an increasing number of patients with low or intermediate pre-test probability of PE. In 2000, no patient with a low or intermediate RGS underwent a D-dimer test. In 2005 this number was 21.3% and in 2008 was 31.9%. Notably, our data show that when the D-dimer was negative in such patients and PE was not diagnosed on CTPA (Table 4). Among those with high pre-test probability, the D-dimer was always positive when performed.
Since the increase in CTPA may be mirrored by a corresponding decrease in V/Q scans, we were interested as to whether the number of V/Q performed for the diagnosis of PE decreased accordingly (Figure 3). The installation and availability of another CT scanner in 2005 resulted in 19% drop in V/Q scans compared to 2000. By 2008, the number of V/Q scans being performed for the diagnosis of PE dropped by 31% compared to 2005 (Table 5), and by 44% compared to 2000. Table 5 also illustrates the changes in ED visits and hospital admissions for the index years 2000, 2005 and 2008.
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Figure 3.
Number of ventilation-perfusion scans (V/Q) performed for the diagnosis of PE from 2000 to 2012.
Results
Over the study period (2000 to 2010), there was a 27-fold increase in the total number of CTPA (Figure 1) without a corresponding increase in yield. The total number of CTPA in the three index years 2000, 2005 and 2008 were 84, 1114 and 2287 respectively. While the number of CTPA ordered increased in all departments, the ED had the largest increase. The numbers of scans performed in the ED per 100 visits were 0.14 in 2000, 1.82 in 2005 and 2.58 in 2008. The ED also had the steepest decline in the percentage of scans positive for PE (Figure 2).
(Enlarge Image)
Figure 1.
The number of CTPA performed per calendar year from 2000 to 2011. The dark bars and percentages are the CTPA that were positive for PE.
(Enlarge Image)
Figure 2.
Number of CTPA by hospital department for the index years 2000, 2005 and 2008. The largest increase occurred in the emergency department (ED) which also had the steepest decline in positive yield (% above bars).
Justification for CTPA
We assessed whether the use of CTPA is justified in those with low or intermediate pre-test probability by the finding of an alternative diagnosis that might explain the patient's symptoms. The frequency of alternate diagnoses found on CTPA was as follows: ED: 10%, Medicine: 5%, Surgery: 3%; p = 0.08. When we examine the data more closely, only 3.2% of potentially avoidable CTPA (low or intermediate pre-test probability and negative D-dimer) had an alternative diagnosis that was neither previously known nor evident on a chest radiograph performed prior to the CTPA.
Findings on Prior Chest X-ray
13% of the patients did not have a prior chest X-ray defined as within 48 hours of CTPA. Among those who did undergo a chest X-ray, the findings were as follows: 40% normal, 14% pleural effusion, 11% pulmonary edema, 6% atelectasis, 6% infiltrate, and 10% other.
Patients Undergoing CTPA
In contrast to 2000 and 2005, those undergoing CTPA in 2008 were significantly younger and less acutely ill as evidenced by their higher oxygen saturation and lower respiratory rate (Table 1). Moreover, patients in 2008 were much less likely to have any risk factors for thrombosis or a prior history of venous thromboembolism. There was an increase in the use of CTPA in patients with chest pain, and for "other" indications (Table 1). The increase in number of scans ordered was accompanied by a significant drop in the diagnosis of PE from 22.6% in 2000 to 13% in 2010. We also noted a change in the size and location of pulmonary emboli detected over time: in 2008, a greater proportion of PE was found distal to the lobar arteries in the segmental or sub segmental branches (Table 2). Since younger patients and women may be more at risk from the potential carcinogenic effects of ionizing radiation, we also examined age and gender in our sample. The number of CTPA performed on women under the age of 40 years increased significantly over the study period (Table 1). While 11.8% of all CTPAs performed were on women less than 40 years of age, the presence of a PE in this cohort was lower than in all CTPAs reviewed (9.1% versus 17.7%).
Pre-test Probability
Across all years, physicians ordering CTPA rarely documented the pre-test probability of PE in the patients' medical records (Table 3). Our calculation of pre-test probability based on the RGS showed that more patients with low pre-test probability of PE underwent CTPA in later years (Table 3). Overall, PE was present on CTPA in 9.3% of patients with a low pre-test probability, 20.9% patients with an intermediate pre-test probability and 29.6% with a high pre-test probability of PE. Slightly over one fifth (22.2%) of patients with a high pre-test probability of PE received any form of anticoagulation prior to undergoing CTPA.
Use of D-dimer
D-dimer was assessed in an increasing number of patients with low or intermediate pre-test probability of PE. In 2000, no patient with a low or intermediate RGS underwent a D-dimer test. In 2005 this number was 21.3% and in 2008 was 31.9%. Notably, our data show that when the D-dimer was negative in such patients and PE was not diagnosed on CTPA (Table 4). Among those with high pre-test probability, the D-dimer was always positive when performed.
V/Q Scanning
Since the increase in CTPA may be mirrored by a corresponding decrease in V/Q scans, we were interested as to whether the number of V/Q performed for the diagnosis of PE decreased accordingly (Figure 3). The installation and availability of another CT scanner in 2005 resulted in 19% drop in V/Q scans compared to 2000. By 2008, the number of V/Q scans being performed for the diagnosis of PE dropped by 31% compared to 2005 (Table 5), and by 44% compared to 2000. Table 5 also illustrates the changes in ED visits and hospital admissions for the index years 2000, 2005 and 2008.
(Enlarge Image)
Figure 3.
Number of ventilation-perfusion scans (V/Q) performed for the diagnosis of PE from 2000 to 2012.