Ultrasound (Doppler scan) is not 100 percent effective at detecting a deep vein thrombosis, a life-threatening blood clot that can dislodge and travel to the lungs and be fatal.
Percentage of DVT’s Missed by Ultrasound
“Sensitivity and specificity of ultrasound detecting DVT in the leg above the knee is 97% and 94%, respectively, meaning, while they are very accurate, it can miss it,” explains Dr. Kurtis Kim, MD, a vascular surgeon at Mercy Medical Center in Baltimore.
Dr. Kim continues, “This stresses the importance of seeing a specialist, as at times, even with negative ultrasound, physicians initiate anticoagulation due to strong clinical suspicion.”
If a physician suspects a deep vein thrombosis – even in the absence of a positive ultrasound result – the doctor will prescribe anticoagulant medication (blood thinners).
What would make a doctor suspect a DVT if the ultrasound is negative?
The physician knows that the ultrasound will, on average, miss a very small percentage of deep vein thromboses detection. But what brought the patient into the exam room in the first place?
Suppose both the patient’s legs are swollen. There is no pain or redness. A week prior the patient had back surgery and reports that for the past week he’s been doing way more sitting than usual.
The ultrasound of his legs is negative; no apparent DVT.
A doctor won’t have a high suspicion of a blood clot due to this patient’s presentation and medical history.
The suspicion for DVT when both legs are swollen equally isn’t very high, especially since excessive sitting (such as that can occur after back surgery) can cause edema or fluid retention in the legs.
But if a patient presents with only one leg newly swollen, and it has a reddish color, and the calf area hurts regardless of activity or rest – the doctor will suspect a deep vein thrombosis even if the ultrasound is negative.
“Unlike CT or X-ray, accuracy of ultrasound is highly operator-dependent, so finding a good vascular specialist and associated vascular lab is important,” says Dr. Kim.
Specializing in minimally invasive procedures, Dr. Kim combines medical expertise with a caring approach to diagnose and treat patients with circulatory issues including leg pain, swelling and blood clots in the legs and lungs.
Lorra Garrick has been covering medical, fitness and cybersecurity topics for many years, having written thousands of articles for print magazines and websites, including as a ghostwriter. She’s also a former ACE-certified personal trainer.