DVT diagnosis
Epidemiology § 1 in 1000 § Case fatality of 1-5% § Very age dependant Morbidity § Post-thrombotic syndrome in up to one third § Chronic pain § Swelling § Ulceration § Can occur early or have a latency of up to 10 years § 28% at 5 years § Half this with compression stockings for 2 years Pre- test probability § Active cancer incl. treatment within the previous 6 months 1 § Paralysis, plaster 1 § Bed >3 days, surgery within 4 weeks 1 § Tenderness along veins 1 § Entire leg swollen 1 § Calf swollen >3cm 1 § Pitting oedema 1 § Collateral veins 1 § Alternative diagnosis likely -2
§ Low risk = 0 (3% risk) § Moderate risk = 1-2 (17% risk) § High risk = 3 or more (75%) § Not recommended for patients with previous VTE/ pregnancy, they should all have imaging
D-dimers § Fibrinogen is a large glycoprotein with 3 pairs of disulphide bonded polypeptide chains § N-terminal, E-domain and 2 outer D-domains § Cleavage of a small peptide results in fibrin monomer formation § Monomers polymerize and form insoluble fibrin § Catalysed by activated factor XIII § Plasmin cleaves the polymer to yield soluble fragments § Throughout each breakdown step the y-y links which connect the D-domains are retained, so that d-dimers are formed
§ D-dimer assays § All use monoclonal antibodies § Techniques include turbidimetry, latex particle agglutination, fluorescence immunoassay, immunofiltration tests and ELISA § ELISA methods are generally more sensitive than the latex agglutination § Discrepancies in comparability of various assays § Partly explained by using combinations of monoclonal antibodies with differing specifity and affinity § Different commercial calibrants § Citrated plasma is the sample type of choice, as some X-oligomers may be consumed in clot formation § Serum samples could lead to false negative values § D-dimers to exclude thrombosis § Absence of a rise in d-dimers implies thrombosis is not occurring § Negative predictive value – requires highly sensitive tests § False positive results are common in hospital patients § Age of the clot § Return to normal 3 months after a DVT § The results of testing after 15 days had a significant effect on the discriminatory value § Position of clot § 20% are isolated calf vein thrombosis § Reduced sensitivity in isolated calf vein thrombosis § Presumably relates to quantity of clot § Heparin use § Levels fall after heparin
Diagnostic imaging § Ascending venography § Gold standard § Detects both distal and proximal thrombi § Diasadvantages § Invasive § Requires contrast § Expensive § Failure rates § Difficult cannulation esp in swollen legs § Contrast preferentially travels in superficial system § Intra-observer variability is high § Inadequate pelvic imaging because of contrast dilution § Ultrasound § Inability to compress the vein lumen § Sensitivity of 89% for all and 97% for proximal DVT § Advantages § Simple § Quick § repeatable § can identify alternative diagnoses § Serial ultrasound § DVTs usually start in the calf, but at time of presentation 80% have more proximal thrombosis § Between 3-20% with distal thrombosis at presentation, extend § Distal DVT that do not extend rarely result in clinically significant emboli § If clinical suspicion high and first scan negative, repeat scan in 1 week will pick up clinically important DVTs § Safe to withhold anticoagulation until repeat scan
§ Diagnosis of recurrent DVT § Abnormalities on US may be detected in up to 70% of patients despite no evidence of recurrent disease in the year following a DVT § Cumulative risk of recurrence is 17% at 2 years and 28% at 5 years § Compare current US with previous or use venography
Recommended diagnostic strategy § Non-pregnant, 1st event § Pretest probability and D-dimers § Low PTP and negative d-dimers = no imaging incl. serial § In high PTP, need imaging regardless of d-dimer |
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