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1 Department of Radiology, University of Rochester Medical Center, 601 Elmwood
Ave., Box 648, Rochester, NY 14642.
2 University of Rochester School of Medicine and Dentistry, Box 601, Rochester,
NY 14642.
3 Clinical Research Center, University of Rochester Medical Center, Box MED/CRC,
Rochester, NY 14642.
4 Department of Medicine, University of Rochester Medical Center, Rochester, NY
14642.
Received March 11, 2002;
accepted after revision June 18, 2002.
Supported in part by the Division of Research Resources-GCRC, grant 5 MO1
RR00044, and the Society of Radiologists in Ultrasound.
Abstract
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SUBJECTS AND METHODS. In this randomized prospective study, patients were assigned to two groups. In one group, the deep calf veins were routinely evaluated in their entirety, and in the other group the calf was not evaluated unless the patient had symptoms or physical signs in the calf, in which case only the areas of symptoms or physical signs were evaluated. Patients were followed up for 3 months by medical record review, physician surveys, and telephone calls. An adverse outcome was a propagated deep venous thrombosis into the thigh or a pulmonary embolus. Examination times were recorded when possible.
RESULTS. Of the 235 patients in the group in which the deep calf veins were routinely evaluated, we saw no adverse outcomes (0.0%; 97.5% one-sided confidence interval [CI], 0.6-1.6%). Of the 261 patients in the group in which the calf was only evaluated if there were signs or symptoms, we saw two adverse outcomes (0.8%; 95% CI, 0.1-2.7%).
CONCLUSION. We found no significant difference in adverse outcomes in patients undergoing a protocol in which the deep calf veins were routinely evaluated or a protocol in which the calf was evaluated only if physical signs or symptoms were present.
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Patient Groups
For 2 years (March 21, 1999—March 29, 2001), we attempted to include
all patients presenting to our laboratory for suspected deep venous thrombosis
of the leg who were 18 years or older. Of 2071 patients who presented to our
laboratory over this time, 535 were missed, 1030 were ineligible for the study
on the basis of our exclusion criteria, and 10 patients were lost to
follow-up. Missed patients were those patients who presented for suspected
deep venous thrombosis but were not requested to participate in the study or
to sign an informed consent form. Patients were frequently missed if they
presented after hours. Exclusion criteria included the following: the patient
was on anticoagulation therapy at the time of the baseline sonogram, had an
inferior vena cava filter, was incompetent or refused to sign informed
consent, had deep venous thrombosis in the thigh, or had indeterminate
findings on thigh sonography. We excluded patients with deep venous thrombosis
in the thigh because our evaluation specifically focused on comparing two calf
sonographic protocols for potential subsequent complications related to
missing isolated calf thrombi. Patients were excluded because of the following
reasons: anticoagulation therapy (n = 336), refusal to participate
(n = 255), incompetent to sign informed consent (n = 312),
deep venous thrombosis of the thigh (n = 52), inferior vena cava
filter (n = 14), and other (n = 61). The specific
indications for leg sonography and patient risk factors for the development of
either a pulmonary embolus or deep venous thrombosis were recorded.
The resulting population included 235 patients in the complete calf protocol group (149 women, 86 men; age range, 19-89 years; mean age, 49.0 years) and 261 patients in the incomplete calf protocol group (178 women, 83 men; age range, 18-88 years; mean age, 48.9 years). Sonography was ordered for leg symptoms or signs of deep venous thrombosis in 192 patients (81.7%) in the complete calf protocol group and in 206 patients (78.9%) in the incomplete calf protocol group. Examinations were ordered for suspected pulmonary emboli in 19 patients (8.1%) in the complete calf protocol group and in 29 patients (11.1%) in the incomplete calf protocol group and for both symptoms and signs and a suspected pulmonary embolus in five patients (2.1%) in the complete calf protocol group and seven patients (2.7%) in the incomplete calf protocol group. A variety of other indications for ordering leg sonography were found in 13 patients (5.5%) in the complete calf protocol group and 16 patients (6.1%) in the incomplete calf protocol group. No reasons were indicated for ordering the examinations in 12 patients (5.1%) in the complete calf protocol group and in 15 patients (5.7%) in the incomplete calf protocol group. Table 1 summarizes the risk factors for the development of a deep venous thrombosis or pulmonary embolus in these groups.
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Patient Follow-Up
Patients were followed up for 3 months by medical record review, physician
surveys, and telephone calls. An adverse outcome was a propagated deep venous
thrombosis into the thigh or a pulmonary embolus. We considered adequate
follow-up to be sufficient information obtained by either telephone
conversations with the patient, contact with the patient's primary care
provider, or review of the medical record to determine whether a pulmonary
embolus or deep venous thrombosis in the leg had developed in the month after
baseline sonography.
Most patients in both groups were followed up by at least a telephone call, with 227 (96.6%) of 235 patients in the complete calf protocol group contacted and 250 (95.8%) of 261 patients in the incomplete calf protocol group contacted. The remaining eight patients (3.4%) in the complete calf protocol group and 11 patients (4.2%) in the incomplete calf protocol group could not be contacted by telephone, but follow-up was considered to be adequate on the basis of medical record review. Follow-up imaging to exclude either a pulmonary embolus or a propagated deep venous thrombosis occurred in a small percentage of patients in both groups. Thirteen patients (5.5%) in the complete calf protocol group underwent subsequent imaging (10 patients, sonography of the leg; two patients, pulmonary angiography; and one patient, contrast venography), and 15 patients (5.8%) in the incomplete calf protocol group underwent subsequent imaging (10 patients, sonography of the leg; three patients, ventilation—perfusion lung scintigraphy; one patient, chest CT angiography; and one patient, contrast venography). The time and reason for all patient deaths were recorded.
Statistical Analysis
We used the binomial distribution for proportions to estimate the
confidence interval (CI) for the rates of adverse outcomes. The mean
examination times were compared using an independent Student's t
test. A p value of less than 0.05 was considered significant.
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Table 2 shows the type of examination actually performed (complete calf, focal calf, or no calf examination) and whether the deep calf veins could be satisfactorily visualized (diagnostic vs indeterminate). One hundred fifty patients (57.5%) in the incomplete calf protocol group had their calves evaluated, either focally or completely, for signs or symptoms; 111 patients (42.5%) in this group did not have their calves evaluated. Complete examinations of the calves were performed in 211 patients (89.8%) in the complete calf protocol group. In the remainder of patients in this group, focal calf examinations were performed (n = 10), or the calf was not evaluated (n = 14) in violation of protocol.
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Seven isolated deep venous thrombi of the calf were detected (Fig. 1). Four of these occurred in the incomplete calf protocol group (1.5%; 95% CI, 0.4-3.9%) versus three in the complete calf protocol group (1.3%; 95% CI, 0.3-3.7%). Four of these patients were treated with anticoagulation therapy. No subsequent bleeding complications resulted, and none of the seven patients had propagation of the thrombus into the thigh or a pulmonary embolus. Risk factors for the development of thrombosis in these individuals included smoking (n = 6), prior history of deep venous thrombosis (n = 4), and recent surgery (n = 3). None of these individuals had a history of malignancy, trauma, or the use of birth control pills.
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Two complications occurred in the incomplete calf protocol group (0.8%; 95% CI, 0.1-2.7%) compared with no complications in the complete calf protocol group (0.0%; 97.5% one-sided CI, 0.0-1.6%) (Table 3). One patient in the incomplete calf protocol group, who was referred because of diffuse calf symptoms, underwent a complete calf evaluation at the time of initial evaluation and developed a deep venous thrombosis of the thigh 25 days later. The findings of the initial leg sonography, including imaging of the calf, in this patient were negative, and the patient had no known risk factors for thrombosis. The other patient with a complication in the incomplete calf protocol group also presented with symptoms in the calf. The patient developed a subsequent pulmonary embolus confirmed 41 days after initial leg sonography by a high-probability ventilation—perfusion lung scan. The findings of an initial focal sonographic evaluation of the calf of the area of symptoms were negative. This patient was at high risk for thrombosis because of multiple risk factors including protein S deficiency, a prior history of deep venous thrombosis, and smoking. None of the 125 patients who had no calf evaluation (0.0%, 97.5% one-sided CI; 0.0-2.9%) developed a complication.
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Fourteen patients died of causes other than a pulmonary embolus, with seven of these in the complete calf protocol group (3.0%; 95% CI, 1.2-6.1%) and seven in the incomplete calf protocol group (2.7%, 95% CI, 1.1-5.5%) (Table 3).
Examination times were available for 85 patients with a unilateral leg examination with a completely diagnostic calf evaluation and for 57 patients with a unilateral leg examination in which the calf was not evaluated. The mean examination time was significantly shorter (p < 0.0001) for the group in which the calf was not evaluated (22.8 ± 13.7 min vs 32.4 ± 14.1 min in the other group).
Other documented findings in the lower leg besides a deep venous thrombosis occurred in a total of 41 patients (8.3%, 95% CI, 6.0-11.0%) with 22 of these patients in the complete calf protocol group (9.4%; 95% CI, 6.0-13.8%) and 19 of these patients in the incomplete calf protocol group (7.3%; 95% CI, 4.4-11.1%). Most other findings were fluid collections in the calf in 19 patients in the complete calf protocol group and in 18 in the incomplete calf protocol group. Most of the fluid collections were considered to be Baker's cysts. Other findings included superficial venous thrombi (two in the complete calf protocol group and one in the incomplete calf protocol group) and a small foot lesion identified in a patient in the complete calf protocol group, which was resected and pathologically characterized as an organized hematoma.
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Both protocols were safe, with no significant difference found between the complete calf protocol and incomplete calf protocol groups in propagated deep venous thrombosis into the thigh and subsequent pulmonary emboli. Two patients in the incomplete calf protocol group had these complications. However, each of these patients presented with calf symptoms, with one patient undergoing a complete calf evaluation and the other, a focal examination directed to the area of symptoms. No patients who did not have their calves evaluated presented with subsequent pulmonary emboli or a propagated deep venous thrombosis into the thigh. Our results suggest that not performing routine complete calf sonography on patients without calf symptoms or signs does not increase their subsequent risk of clinically significant propagation of thrombi into the thigh veins or pulmonary emboli.
We also documented a potential time-savings of approximately 10 min per leg between an examination in which the calf is completely evaluated and one in which the calf is not evaluated at all. A complete calf examination could take substantially longer in patients who have large legs or are immobile. A less time-consuming sonography of the leg for deep venous thrombosis could translate into increased patient throughput.
We found a large number of indeterminate findings on calf evaluations for the presence of a deep venous thrombosis, both in the complete calf protocol group and in patients in the incomplete calf protocol group. The high rate of indeterminate findings on calf evaluations in our laboratory most likely was due to our strict requirement that all segments of the paired deep calf veins be visualized satisfactorily to label a study as diagnostic and the relatively large number of immobile patients in our study population because study participants were often drawn from relatively sick inpatients and emergency department patients. Many of our calf examinations called "indeterminate" had segments of the individual calf veins visualized but not their entire lengths, raising our rate of indeterminate examinations. Differences in patient populations and in criteria for a diagnostic calf evaluation have been found previously to lead to a large range in the reported rates of indeterminate calf studies, with these rates varying between 9.3% and 82.7% [19].
Our study randomized patients into two groups (complete calf protocol and incomplete calf protocol groups) on the basis of a protocol that specified evaluating the deep calf veins routinely in their entirety in the complete calf protocol group and only evaluating the calf when necessary in the incomplete calf protocol group. It would be inappropriate not to evaluate the calf at all, in patients with signs or symptoms, in the incomplete calf protocol group because sonography can, on occasion, reveal the cause of the patients' symptoms or signs in the calf, including a ruptured Baker's cyst, abscess, or tumor [7]. Other findings in the lower leg explained patient symptoms or signs in 8.3% of patients, with similar percentages in both the complete calf protocol and the incomplete calf protocol groups.
Our study had several limitations. As with any clinical trial, crossovers existed between study groups. A small percentage of patients in the complete calf protocol group had either focal or no calf evaluations, despite being randomized to undergo a complete examination. This omission did not affect our study results because none of these patients had a subsequent complication, despite an abbreviated calf evaluation. Conversely, more than half of the patients in the incomplete calf protocol group had either complete or focal calf examinations. This change was permitted by protocol because these patients had physical signs or symptoms in the calf that required either a complete or a limited evaluation directed to the area of clinical concern.
A relatively large number of potential patients were missed, with most of these presenting after hours. If these patients had been included, our results may have been altered. However, we lacked the resources to recruit patients 24 hr a day, 7 days a week to avoid this potential bias.
A relatively small percentage of our patients were documented on follow-up imaging to be negative for a propagated thrombosis into the thigh or pulmonary emboli. Lack of follow-up imaging serves as a potential limitation in identifying patients with silent pulmonary emboli or patients with or without leg symptoms who have unsuspected deep venous thrombosis in the thigh. However, our methods of determining patient outcomes, including telephone calls in most patients, were sufficient to identify clinically significant adverse events.
The rate of detection of isolated calf thrombi was approximately the same for both protocols, 1.5% for the incomplete calf protocol group versus 1.3% for the complete calf protocol group. The rate of detection of isolated calf thrombi was slightly lower, although within the range of rates (2.1-4.8%) reported in the literature [20,21,22]. Four of the seven patients were treated with anticoagulation therapy, and three were not. No bleeding complications from anticoagulation therapy occurred, and none of these patients presented subsequently with either propagated thigh deep venous thromboses or pulmonary emboli.
Isolated calf thrombi occurred uncommonly [20,21,22] and were detected at nearly identical rates in the complete calf protocol and the incomplete calf protocol groups. Our results suggest that clinically significant calf thrombi are present only in patients with physical signs or symptoms in the calf at the site of the thrombus.
In summary, no significant risk exists in performing a calf examination only if there are symptoms or physical signs in the calf and in not evaluating the calf otherwise. The calf should not be part of the routine leg sonography protocol for suspected deep venous thrombosis unless signs or symptoms are present in the calf.
Acknowledgments
We thank Valerie Bates for her secretarial assistance and the sonographers
in the department of radiology for the time and effort devoted to this
project.
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