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Flashcards in Thrombophia Deck (11):

Principle of RVV

Russell’s viper venom (RVV) activates factor X, leading to a fibrin clot in the presence of factor V, prothrombin, phospholipid and calcium ions. A LAC prolongs the clotting time by binding to the phospholipid and preventing the action of RVV. dilution of the venom and phospholipid makes it particularly sensitive for detecting a LAC.7 Because RVV activates factor X directly, defects of the contact system and factor VIII, IX and XI deficiencies do not influence the test. The DRVVT should be combined with a platelet/phospholipid neutralization procedure to add specificity and this is incorporated into several commercial kits.


Low protein c

oral anticoagulant therapy.
sepsis (especially meningococcal septicaemia), liver disease
sickle cell disease
early postoperative period.


What is lupus anticoagulant

LACs are immunoglobulins that bind to certain proteins when bound to phospholipid. The effective sequestration of phospholipid can then cause prolongation of phospholipid-dependent coagulation tests such as the prothrombin time (PT) or activated partial thromboplastin time (APTT).


Method of dilute rvv test

Place 0.1 ml of pooled normal plasma and 0.1 ml of dilute phospholipid reagent in a glass tube at 37°C. Add 0.1 ml of dilute RVV and, after warming for 30 s, add 0.1 ml of CaCl2. Record the clotting time. Repeat the sequence using the test plasma. Calculate the ratio of the clotting times of the test and control (normal pool) plasma.


What is dilute RVV ratio

ratio of the clotting times of the test and control (normal pool) plasma usually up to 1.02 s
Greater than this suggests lac


DDx for driving ratio > 1.05s

ABN F2, 5, 10 f'gen or inhibitor


How to differentiate if LAC vs inhibitor

mixing test first to confirm the presence of an inhibitor and to exclude a factor deficiency then to confirm Apab
LAC- plt neutralisation procedure


Criteria for catastrophic apls

Evidence of involvement of 3 or more organs
Development over a week
Confirmation of histopatholohy if small vessel occlusion
Lab confirmation of apls

Definite if all 4 present
Probable if 1,2 and 4. 1,3,4 with a third event


Other things occuring with catastrophic apls

Haemolytic anaemia


Method or protein c testing

Elisa- sandwich method, cheap, rapid,
EIA- laurell rocker
Commercial, expensive, small batch size


Ddx arterial and venous clot

§   Defects in clot lysis (Dysfibrinogenemia*, Deficiency of plasminogen-activator inhibitor type 1)

§   Metabolic (Homocysteinemia)

§   Platelet disorders (HIT, Myeloproliferative disorders, PNH, Polycythemia vera (with thrombocytosis))

§   Hyperviscosity (Polycythemia vera, Waldenström’s macroglobulinemia, Sickle cell anemia, Acute leukemia)