Deep vein thrombosis laboratory tests

Editors-in-Chief: C. Michael Gibson, M.S., M.D. Associate Editor-In-Chief: Ujjwal Rastogi, MBBS [mailto:urastogi@perfuse.org]

Overview
Deep vein thrombosis is a common condition seen in the Emergency Department. Standard of care for diagnosis of DVT includes a combination of a clinical pre-test probability rule known as Well's criteria, D-dimer blood testing, and Radiology department ultrasound.

D-dimer
 In a low-probability situation, current practice is to commence investigations by testing for D-dimer levels. This cross-linked fibrin degradation product is an indication that thrombosis is occurring, and that the blood clot is being dissolved by plasmin. A low D-dimer level should prompt other possible diagnoses (such as a ruptured Baker's cyst, if the patient is at sufficiently low clinical probability of DVT.

It should be noted that latex D-dimer assays are insensitive and have no role in screening for deep vein thrombosis.

Other blood tests
Other blood tests usually performed at this point are:
 * complete blood count
 * Primary coagulation studies: PT, APTT, Fibrinogen
 * liver enzymes
 * renal function and electrolytes
 * prostate specific antigen measurement in men over the age of 50.

Test
However, these medical signs do not perform well and are not included in clinical prediction rules that combine best findings in order to diagnose DVT.
 * Homan's test: is said to be present when passive dorsiflexion of the ankle by the examiner elicits sharp pain in the calf.. A positive Homans sign does not positively diagnose DVT (poor positive predictive value), and anegative Homans sign does not rule out the DVT diagnosis (poor negative predictive value).
 * Pratt's sign: Squeezing of posterior calf elicits pain