In a recent Medscape article, a study is highlighted regarding serial DVT ultrasound (including doppler of iliacs) can rule out DVT in pregnancy. How about that?! This is a follow up to that last post regarding “best test” for first diagnosis of suspected DVT. The article is stated below:

“Conducting serial compression ultrasonography with Doppler imaging of the iliac vein over the course of 7 days can rule out deep-vein thrombosis (DVT) in symptomatic pregnant women, according to a prospective cohort study.

Wee-Shian Chan, MD, from the Department of Medicine, BC Women’s Hospital and Health Centre, Vancouver, British Columbia, Canada, and colleagues report their findings in an article published online January 14 in the Canadian Medical Association Journal.

Increasingly, healthcare providers suspecting DVT turn to serial venous compression ultrasonography to diagnose the blood clots; if negative, Doppler imaging is added to overcome ultrasound’s lack of sensitivity in diagnosing isolated iliac DVTs in pregnant women for whom pelvic veins cannot be compressed. The diagnostic approach is noninvasive, widely available, and does not expose the fetus to ionizing radiation, and thus has become the standard of practice for diagnosing DVT in pregnant women. Because no study has validated this approach, Dr. Chan and colleagues sought to evaluate the diagnostic accuracy of using serial compression ultrasonography and Doppler imaging of the iliac veins among symptomatic pregnant women during a 7-day period.

They focused on pregnant women consecutively referred for investigation of DVT from August 2002 to September 2010 at 4 Canadian centers and enrolled 221 women who had had a suspected first episode of DVT. Exclusion criteria included receipt of anticoagulant therapy for more than 48 hours before presentation, suspicion of pulmonary embolism, concomitant cardiac or pulmonary disease, and inability or lack of willingness to return for follow-up.

Trained technicians performed ultrasound examination of the symptomatic leg by compression of the proximal veins (ie, along the length of the femoral vein from the inguinal canal and the popliteal veins to the level of the calf trifurcation with Doppler studies of the iliac vein). If the first test results were negative for DVT, blood thinners were withheld and testing was repeated after 2 to 4 days and again after 6 to 8 days. Blood thinners were prescribed if results were positive. The research team excluded DVT based on full compressibility of the femoral and popliteal veins and normal Doppler imaging of the iliac veins.

“The overall prevalence of deep vein thrombosis in our study cohort was 7.7% (95% [confidence interval,] 4.9% – 12.0%),” Dr. Chan and colleagues write. “The iliac or femoral veins, or both, were involved in 65% (11/17) of cases. Of these, 2 (12%) cases were isolated to the iliac vein, and 4 (24%) were isolated to the femoral vein.”

Some 94% of DVT were detected by the initial compression ultrasonography with Doppler imaging. The serial testing that followed did not detect any new thromboses, the research team writes. “Our strategy of serial compression ultrasonography combined with Doppler imaging of the iliac veins appears to reliably exclude clinically important deep vein thrombosis,” the authors write.

Added Value Unclear

Additional studies are needed to determine what is better for pregnant women: ultrasonic testing with Doppler imaging or single whole-leg ultrasound, “the only other diagnostic strategy that has been formally validated for DVT suspicion in pregnancy,” Grégoire Le Gal, MD, from the University of Brest, France, told Medscape Medical News. Dr. Le Gal and colleagues found that conducting a single ultrasound test may rule out diagnosis of DVT in pregnant and postpartum women.

“In nonpregnant patients, the 2 strategies have been compared and showed similar safety. The use of single whole-leg ultrasound is convenient, because patients don’t need to come back for serial testing. But, on the other hand, it is more time-consuming and it leads to a positive diagnosis of DVT in a higher proportion of patients, mainly because all distal DVT are detected — and therefore treated — with anticoagulants, when this approach is used,” Dr. Le Gal says. Using serial compression ultrasonic testing, “only the distal DVT that extend proximally are detected on serial tests and treated.”

Dr. Le Gal also noted that in Dr. Chan’s study, a Doppler interrogation was performed in all patients. “Physicians willing to implement this diagnostic strategy in their clinical practice need to take this into account. Unfortunately, the yield of this test was not provided in the manuscript. Therefore, it is impossible to know the exact added value of this test as compared with a serial compression ultrasonography without Doppler,” Dr. Le Gal told Medscape Medical News.

Because it is unethical to use leg venography with fluoroscopy or computed tomographic angiography in pregnant women to confirm DVT diagnoses, Dr. Chan and colleagues assumed that all diagnosed abnormalities were DVT. Another study limitation was that the current study showed a lower prevalence of DVT compared with 2 previous studies involving pregnant women; this could exaggerate the negative predictive value. In addition, the study investigators were thrombosis specialists based in secondary and tertiary referral centers, which raises the question of generalizability; because patients were recruited from a range of settings, however, the researchers argue that the study’s results are generalizable to most community-based hospitals.

“Our study highlights the importance of iliac vein visualization in symptomatic pregnant women,” the authors conclude. They add that the research also “shows that serial compression ultrasonographic studies with iliac vein visualization performed over a 7-day period can reliably exclude deep vein thrombosis in symptomatic pregnant women and that it is likely safe to withhold anticoagulation in women with negative imaging results.”

CMAJ. Published online January 14, 2013. Full text

A recent highlight from Mescape discusses a study published in Annals of Internal Medicine by Linkins et al. about how the D-Dimer may or may not help in DVT evaluation, and how ultrasound relates to the diagnosis of DVT in varying groups based on pre-test probability. Interesting read, and definitely something to make me go “hmmmm….”. The study concludes that in a certain group, a selective d-dimer testing paradigm can be of utility. The Mescape are states:

“It is best to base ᴅ-dimer testing on a patient’s clinical pretest probability (C-PTP) for deep vein thrombosis (DVT), rather than testing all patients who present with symptoms of first DVT episode. This strategy can exclude DVT in more patients without increasing missed diagnoses, according to a randomized, multicenter, controlled trial in 1723 patients at 5 medical centers in Canada.

Lori-Ann Linkins, MD, an assistant professor in the Division of Hematology and Thromboembolism, Department of Medicine, McMaster University in Hamilton, Ontario, Canada, and colleagues published their findings in the January 15 issue of the Annals of Internal Medicine.

ᴅ-dimer testing is sensitive but not specific for identifying DVT. Selectively testing ᴅ-dimer levels lowered the proportion of patients who needed ultrasonography and decreased the percentage of patients who required ᴅ-dimer testing by 21.8% (95% confidence interval [CI], 19.1% – 24.8%).

“In this trial comparing uniform with selective ᴅ-dimer testing in patients with suspected first DVT, a selective strategy — which used a higher ᴅ-dimer threshold to exclude first acute DVT in outpatients with low C-PTP and omitted ᴅ-dimer testing in outpatients with high C-PTP and all inpatients — was as safe as and more efficient than the uniform testing strategy, which used the same threshold to exclude DVT in all patients,” the authors write.

Patients were randomly assigned to the selective testing (n = 860) or uniform testing (n = 863) groups on presentation for suspected first DVT episode. Of the study participants, 1542 (89%) were outpatients and 181 (11%) were inpatients.

All patients in the uniform testing group underwent ᴅ-dimer testing. Levels less than 0.5 μg/mL were considered negative, and levels of 0.5 μg/mL or higher were considered positive. For patients with positive results, ultrasonography of the proximal veins in the symptomatic legs was conducted; patients with normal ultrasonogram and high C-PTP had ultrasonography repeated on the same legs 6 to 8 days later.

Patients in the selective testing group only underwent ᴅ-dimer testing if they were outpatients and had low or moderate C-PTP. Outpatients with high C-PTP and all inpatients underwent ultrasonography only. ᴅ-dimer levels in the low C-PTP group were considered negative if they were below 1.0 μg/mL and positive if they were 1.0 μg/mL or above.

For patients in the moderate C-PTP group, ᴅ-dimer levels were considered negative if they were below 0.5 μg/mL and positive if they were 0.5 μg/mL or above. Patients with positive results had ultrasonography, and patients with normal ultrasonogram and moderate or high C-PTP had ultrasonography repeated 6 to 8 days later.

Of the patients in the uniform testing group, 859 (99.5%) had ᴅ-dimer testing, 505 (58.5%) had initial ultrasonography, and 334 (38.7%) had ultrasonography repeated after 6 to 8 days.

Positive ᴅ-dimer results were found in 506 patients (418 outpatients and 88 inpatients), and negative results were found in 353 patients (351 outpatients and 2 inpatients). Four patients had no test. DVT was diagnosed by initial ultrasonography in 56 ᴅ-dimer-positive patients (11.1% of the 506 ᴅ-dimer-positive patients and 6.5% of 863 patients in the uniform testing group). None of the 81 patients with low C-PTP and a ᴅ-dimer level between 0.5 and 1.0 µg/mL had DVT on ultrasonography.

“You’re Not Missing Cases”

Venous thromboembolism (VTE) was diagnosed during follow-up in 4 patients: 0.8% (95% CI, 0.2% – 2.0%) of the 506 ᴅ-dimer-positive patients with normal initial ultrasonogram and 0.5% (95% CI, 0.1% – 1.3%) of the 798 patients without DVT on initial testing who were still in the study at 3-month follow-up. No outpatients with low C-PTP and ᴅ-dimer levels between 0.5 and 1.0 μg/mL were diagnosed with VTE during follow-up. No VTE was diagnosed during follow-up in any ᴅ-dimer-negative patient (0.0%; 95% CI, 0.0% – 1.1%).

ᴅ-dimer testing was done in 668 of the 860 patients (77.7%), initial ultrasonography was done in 438 patients (50.9%), and ultrasound was repeated after 6 to 8 days in 383 patients (44.5%). ᴅ-dimer results were negative in 288 (80%) and positive in 72 (20%) of the 360 outpatients with low C-PTP.

None of the 288 ᴅ-dimer-negative patients (200 with ᴅ-dimer level < 0.5 μg/mL and 88 with ᴅ-dimer level 0.5 – 1.0 μg/mL) experienced VTE during follow-up (95% CI, 0.0% – 1.3%).

Of the 72 ᴅ-dimer-positive patients, 8 (11%) had DVT diagnosed by ultrasonography during initial testing. No patient with a normal ultrasonogram experienced VTE during follow-up (95% CI, 0.0% – 5.1%).

A total of 132 (43%) of the outpatients with moderate C-PTP were ᴅ-dimer-negative and 176 (57%) were ᴅ-dimer-positive. Two patients had no ᴅ-dimer testing. One ᴅ-dimer-negative patient experienced VTE during follow-up (0.8%; 95% CI, 0.0% – 4.3%), and 5 were lost to follow-up. DVT was diagnosed by ultrasonography during initial testing in 23 (13%) of the 176 ᴅ-dimer-positive patients. One of the 153 ᴅ-dimer-positive patients with normal ultrasonogram developed VTE during follow-up (0.6%; 95% CI, 0.0% – 3.2%); 4 patients were lost to follow-up.

DVT was diagnosed during initial testing in 20 (10.5%) of the 100 outpatients with high C-PTP and the 90 inpatients. VTE was identified during follow-up in 2 patients with normal ultrasonograms (1.1%; 95% CI, 0.1% – 3.8%). One patient was lost to follow-up.

DVT was diagnosed during initial testing in 51 (5.9%) of the selective testing patients. VTE developed during follow-up in 4 (0.5%; 95% CI, 0.1% – 1.3%) of the patients who had no DVT diagnosed during initial testing.

During follow-up, the difference between the groups in the number of VTE events was 0.0 percentage points (95% CI, −0.8 to 0.8 percentage points) in patients not diagnosed with DVT during initial testing and −0.3 percentage points (95% CI, −1.8 to 0.8 percentage points) in favor of selective testing in the outpatient or low C-PTP subgroup.

The difference between the groups in the proportion of those undergoing testing was −21.8 percentage points (95% CI, −24.8 to −19.1 percentage points) for ᴅ-dimer testing and −7.6 percentage points (95% CI, −12.2 to −2.9 percentage points) for ultrasonography, both in favor of selective testing.

The proportion of patients in the outpatient and low C-PTP subgroup who had ultrasonography was 20.0% in the selective testing group and 41.0% in the uniform testing group (difference, −21.0 percentage points in favor of selective testing; 95% CI, −27.6 to −14.2 percentage points).

Daniel J. Giaccio, MD, vice chair of medicine at Lutheran Medical Center in Brooklyn, New York, commented on the study in a telephone interview with Medscape Medical News. Selective testing enabled the researchers to avoid unnecessary ultrasounds, he noted. “In this day and age of cost-effectiveness, and especially with the incentives…for doctors to practice more cost-effective care, [it’s good] to know that you’re not missing cases — you’re actually picking up more,” Dr. Giaccio explained.”