The value of using ultrasound to rule out deep vein thrombosis in cases of cellulitis

The “Things We Do for No Reason” series reviews practices which have become common parts of hospital care but which may provide little value to our patients. Practices reviewed in the TWDFNR series do not represent “black and white” conclusions or clinical practice standards, but are meant as a starting place for research and active discussions among hospitalists and patients. We invite you to be part of that discussion. https://www.choosingwisely.org/

Because of overlapping clinical manifestations, clinicians often order ultrasound to rule out deep vein thrombosis (DVT) in cases of cellulitis. Ultrasound testing is performed for 16% to 73% of patients diagnosed with cellulitis. Although testing is common, the pooled incidence of DVT is low (3.1%). Few data elucidate which patients with cellulitis are more likely to have concurrent DVT and require further testing. The Wells clinical prediction rule with D-dimer testing overestimates DVT risk in patients with cellulitis and is of little value in this setting. Given the overall low incidence, routine ultrasound testing is unnecessary for most patients with cellulitis. ultrasound should be reserved for patients with a history of venous thromboembolism (VTE), immobility, thrombophilia, congestive heart failure (CHF), cerebrovascular accident (CVA) with hemiparesis, trauma, or recent surgery, and for patients who do not respond to antibiotics.

A 50-year-old man presented to the emergency department with a 3-day-old cut on his anterior right shin. Associated redness, warmth, pain, and swelling had progressed. The patient had no history of prior DVT or pulmonary embolism (PE). His temperature was 38.5°C, and his white blood cell count of 18,000. On review of systems, he denied shortness of breath and chest pain. He was diagnosed with cellulitis and administered intravenous fluids and cefazolin. The clinician wondered whether to perform lower extremity ultrasound to rule out concurrent DVT.

WHY YOU MIGHT THINK ULTRASOUND IS HELPFUL IN RULING OUT DVT IN CELLULITIS

Lower extremity cellulitis, a common infection of the skin and subcutaneous tissues, is characterized by unilateral erythema, pain, warmth, and swelling. The infection usually follows a skin breach that allows bacteria to enter. DVT may present similarly, and symptoms can include mild leukocytosis and elevated temperature. Because of the clinical similarities, clinicians often order compression ultrasound of the extremity to rule out concurrent DVT in cellulitis. Further impetus for testing stems from fear of the potential complications of untreated DVT, including post-thrombotic syndrome, chronic venous insufficiency, and venous ulceration. A subsequent PE can be fatal, or can cause significant morbidity, including chronic VTE with associated pulmonary hypertension. An estimated quarter of all PEs present as sudden death.¹

WHY ULTRASOUND IS NOT HELPFUL IN THIS SETTING

Studies have shown that ultrasound is ordered for 16% to 73% of patients with a cellulitis diagnosis.^2,3 Although testing is commonly performed, a meta-analysis of 9 studies of cellulitis patients who underwent ultrasound testing for concurrent DVT revealed a low pooled incidence of total DVT (3.1%) and proximal DVT (2.1%).⁴ Maze et al.² retrospectively reviewed 1515 cellulitis cases (identified by International Classification of Diseases, Ninth Revision codes) at a single center in New Zealand over 3 years. Of the 1515 patients, 240 (16%) had ultrasound performed, and only 3 (1.3%) were found to have DVT. Two of the 3 had active malignancy, and the third had injected battery acid into the area. In a 5-year retrospective cohort study at a Veterans Administration hospital in Connecticut, Gunderson and Chang³ reviewed the cases of 183 patients with cellulitis and found ultrasound testing commonly performed (73% of cases) to assess for DVT. Only 1 patient (<1%) was diagnosed with new DVT in the ipsilateral leg, and acute DVT was diagnosed in the contralateral leg of 2 other patients. Overall, these studies indicate the incidence of concurrent DVT in cellulitis is low, regardless of the frequency of ultrasound testing.

Although the cost of a single ultrasound test is not prohibitive, annual total costs hospital-wide and nationally are large. In the United States, the charge for a unilateral duplex ultrasound of the extremity ranges from $260 to $1300, and there is an additional charge for interpretation by a radiologist.⁵ In a retrospective study spanning 3.5 years and involving 2 community hospitals in Michigan, an estimated $290,000 was spent on ultrasound tests defined as unnecessary for patients with cellulitis.⁶ A limitation of the study was defining a test as unnecessary based on its result being negative.