Deep Venous Thrombosis Diagnostic Modalities
The signs and symptoms of DVT are varied and depend on the severity. Generally, DVTs can cause pain, swelling, tenderness, skin discolouration and increased warmth of the affected area. The signs and symptoms of PE are nonspecific and can include sudden chest pain, dyspnea, tachypnea, hemoptysis, and loss of consciousness (fainting), which often leads to difficulties with diagnosis. Several methods and techniques are currently used for diagnosis.
Although the various methods of DVT detection will be discussed, it is important for health care professionals, patients, family members and caregivers to be educated in the early signs and symptoms. Expert consensus, as noted by the PVA Consortium of Spinal Cord Medicine (2005) guideline for the prevention of thromboembolism, suggests that all extremities should be inspected twice daily for an increase in the calf or thigh venous pattern or circumference, low-grade fever of unknown origin and/or pain, tenderness, or heaviness of an affected extremity. Since individuals can sometimes be asymptomatic, it is also suggested that health care providers, including family and caregivers, be familiarized with risk factors such as lower limb fractures, dehydration, obesity, age, malignancy, congestive heart failure, estrogen therapy, pregnancy, and a history of thrombosis.
Another measure, considered by expert consensus to be important and preventative, is the routine practice of active and passive range of motion exercises. Mobilization and movement of the extremities (with careful consideration of spinal stability in the acute phase) should be essential in the prevention of DVT after a SCI.
Venous ultrasound has become the primary noninvasive diagnostic test for DVTs (Furlan & Fehlings 2007). Furlan and Fehlings (2007) note that ultrasound is well recognized as an important tool in the initial workup of clinically suspected DVT. However, concern exists for ultrasound as a screening tool of asymptomatic DVTs because of relatively low sensitivities in other populations.
Venography is an invasive study whereby contrast dye is injected into the leg veins. It is considered a definitive test for DVT. Diagnosis of DVT is made if an intraluminal-filling defect is noted. Furlan and Fehlings (2007) note that:
Although contrast venography is considered as the gold standard for investigation of symptomatic or asymptomatic DVT, venography has been considered an unsuitable tool for routine assessment of asymptomatic DVT due to its invasive nature, potential complications, technical issues and costs [Kelly et al. 2001; Tapson et al. 1999; Zierler 2004].
D-dimer assay tests are rapid, noninvasive and inexpensive (Gill & Nahum 2000). Fibrin is the main component of thrombus formation and fibrin degradation products include d-dimers (Gill & Nahum 2000). A positive d-dimer test is highly sensitive but lacks specificity since d-dimers are found in other disease states including cancer, congestive heart failure and inflammatory conditions (Raimondi 1993). For example, Masuda et al. (2015) report sensitivity and specificity at 77.3% and 69.2%, respectively, among a sample of 268 individuals with acute traumatic SCI. D-dimer assays have a high negative predictive value, so that when it is negative it is unlikely that the individual has a DVT. However, it has poor positive predictive value so that when it is positive the cause could be a condition other than DVT (i.e. false positive). To illustrate, Akman et al. (2004) reported that the sensitivity and negative predictive values of the D-dimer test were high, at 95.2% and 96.2% respectively, in a group of 68 rehabilitating individuals admitted with a diagnosis of stroke, SCI (n=43%), hip arthroplasty or traumatic brain injury. The specificity and positive predictive value were low, at 55.3% and 48.7%. Therefore, the d-dimer test appears to be a useful and widely available screening test for VTE. It is been utilized to screen for DVT at two weeks after the SCI (Masuda et al. 2015) or on admission to rehabilitation unit from acute care (Eichinger et al. 2018). If levels are high, further investigation is warranted (Wada et al. 2013)
The screening test of choice for asymptomatic DVT needs to be determined. A systematic review on noninvasive diagnosis of DVT from the McMaster Diagnosis of Deep Venous Thrombosis Working Group indicated that: 1) venography is the only reliable test for the diagnosis of asymptomatic DVT; 2) the role of surveillance testing with ultrasound in asymptomatic individuals at high risk of DVT is uncertain; and 3) surveillance testing with impedance plethysmography is not recommended.