It is difficult but there are some things you can look for. From a recent review:
Lower limb deep venous thrombosis (DVT) recurrence represents a diagnostic challenge.
Ultrasound is the first choice examination when DVT is suspected.
This review highlights the validated criteria for DVT recurrence.
An increase in vein diameter between 2 and 4 mm requires further examination.
New diagnostic imaging techniques are currently under evaluation.
Recurrent deep vein thrombosis (DVT) is often suspected in patients after anticoagulant drug withdrawal. The clinical signs can be confused with the onset of post-thrombotic syndrome. For these reasons, diagnosis of DVT recurrence must rely on an accurate method.
Materials and methods
In order to assess this challenging clinical issue, we performed an overview of the literature regarding ultrasound criteria for the diagnosis of recurrent DVT through a Medline search, which included articles published from January 1, 1980 to February 20, 2017.
Eighty-eight publications were found based on the defined keywords, of which nine articles with a relevant abstract were selected. By searching the reference lists of these nine articles, we obtained another 27 relevant articles. A new non-compressible vein or an increase in the diameter of a previously thrombosed vein segment by greater than 4 mm are sufficient to confirm the diagnosis of DVT recurrence. In contrast, an increase in diameter of less than 2 mm enables recurrence to be ruled out. An increase between 2 and 4 mm is deemed equivocal. Criteria based on echogenicity and Doppler venous blood flow are not reproducible. Other diagnostic imaging methods, mainly direct thrombus magnetic resonance imaging, are currently under evaluation.
Ultrasound remains the most useful test for the diagnosis of recurrent DVT. Further imaging tests need to be validated.