LAB BOOK INVESTIGATING BLEEDING DISORDERS Clinical signs of coagulopathies may include petechial or ecchymotic haemorrhages, unexplained persistent haemorrhage or multiple haematomas. Terminology usually describes problems with clotting factors as clotting disorders and problems with platelets as bleeding disorders. CAUSES OF BLEEDING DISORDERS: Coagulopathies (all rare!) • Hepatic disease. Although the liver produces a large number of factors important in coagulation bleeding disorders are uncommon as a consequence of hepatic disease • Vitamin K deficieny may occur as a result of coumerol toxicity • Factor VIII deficiency (classic haemophilia) has been identified in Thoroughbreds, Standardbreds, Quarterhorses and Arabs • deficiency of Von Willebrand’s factor has been identified in Thoroughbreds and a Quarter horse • Prekallikrein deficiencyhas been identified in Belgian horses, American Miniature horses and a Quarter horse • Glanzmann’s thrombasthenia is a rare congential disorder of platelets Vasculitis • Infectious, immune-mediated, toxic and neoplastic diseasesmay all lead to vasculitis and result in coagulopathy (relatively common) • Equine Infectious Anaemia (NOTIFIABLE!) • Equine Viral Arteritis (NOTIFIABLE!) • Anaplasmosis • Piroplasmosis Thrombocytopaenia • Hereditary defects (rare) • Bone marrow disease (see anaemia) • DIC • Excessive haemorrhage • Thrombosis • EIA • Anaplasmosis • Immune-mediated (primary or secondary to infection/neoplasia/drugs) • Vitamin K deficiency (rare) COPYRIGHT © 2015 LIPHOOK EQUINE HOSPITAL. 21 LAB BOOK LAB BOOK DIAGNOSTIC TESTS Diagnostic Tests The diagnosti c tests that are available in practi ce are crude and comprise prothrombin ti me (PT) acti vated parti al thromboplastiThe diagnostic n teststi thatme (aPTT)are available and in bleeding practice are ti crude me. and Further comprise functi prothrombin onal tests time (PT) are activated used as partial research thromboplast toolsin buttime are not available(aPTT) commercially. and bleeding time. All Further tests shouldfunctional be tests compared are used as contemporaneously research tools but are notwith available a control commercially. horse as All reference tests should ranges be are unreliablecompared contemporaneously due to the number with a ofcontrol external horse asfactors reference that ranges may are aff unreliable ect the due test. to theValues number greater of external than factors 20% that above may the controlaffect are the considered test. Values greater abnormal. than 20% Horses above rarely the control develop are considered bleeding abnormal. diathesis Horses and coagulopathiesrarely develop bleeding are diathesismore likely and to manifestcoagulopathies as excessive are more clotti likely tong manifest and thrombus as excessive formati clotting and on thrombus than excessive formation thanand excessiveuncontrolled and uncontrolled haemorrhage. haemorrhage. • PT - (extrinsic pathway) is usually around 10-12 secs and depends on factors I, II, V, VII, and X and will be aff ected by coumarin-type anti coagulants, vitamin K defi ciency, liver damage and general consumpti ve coagulopathiest PT - (extrinsic (DIC).pathway) Factor is usually VII around has the 10-12 shortest secs and half-life depends of on all factors clotti I, II, V,ng VII,factors and X andso generalisedwill be affected clotti by coumarin- ng disorders maytype be detectedanticoagulants, by vitaminproloned K deficiency, PT prior liver to damage prolonged and general aPTT. consumptive coagulopathies (DIC). Factor VII has the shortest half-life of all clotting factors so generalised clotting disorders may be detected by proloned PT prior to prolonged aPTT. • aPTT - (intrinsic and common pathways) is usually around 30-45 secs and depends on factors I, II, V, VIII, IX, X, XI,t &aPTT XII and - (intrinsic will be and aff common ected pathways)by heparin is usually treatment, around 30-45 general secs andconsumpti depends on ve factors coagulopathies I, II, V, VIII, IX, X,(DIC), XI, & vonXII and Willebrand will disease, haemophilia and probably severe hepati c failure. be affected by heparin treatment, general consumptive coagulopathies (DIC), von Willebrand disease, haemophilia and probably • Bleedingsevere tihepatic me- failure.is a crude test of platelet functi on whereby a small stab incision is made in the skin and blood removed every 30 secs with ti ssue (without touching the skin). Bleeding should cease within 5 minutes in normalt Bleeding horses. time Bleeding – is a crude ti testme of is platelet aff ected function by whereby several a smallprocesses stab incision including is made thrombocytopaenia, in the skin and blood removed thrombasthenia, every 30 DIC,secs vasculiti with tissue s, aspirin,(without livertouching and the kidney skin). Bleeding failure. should cease within 5 minutes in normal horses. Bleeding time is affected by • Plateletseveral count processes - isincluding usually thrombocytopaenia, >100 x 109/L thrombasthenia, but is very DIC, suscepti vasculitis, ble aspirin, to liverartefactually and kidney failure. low measured values. If thrombocytopaenia is identi fi ed in EDTA samples then measurement should be repeated on a citrate sample t Platelet count – is usually > 100 x 109/L but is very susceptible to artefactually low measured values. If thrombocytopaenia as the likelyhood of artefactual platelet clumping is reduced when citrate is used as an anti coagulant. Bleeding disordersis identified are generallyin EDTA samples associated then measurement with platelet should counts be repeated < 20 x on10 9a/L. citrate Primary sample diff as theerenti likelyhood als for of artefactualthrombocytopaenia platelet includeclumping immune is reduced mediated when citrate disease, is used DICas an and anticoagulant. liver failure. Bleeding disorders are generally associated with platelet counts < 20 x 109/L. Primary differentials for thrombocytopaenia include immune mediated disease, DIC and liver failure. • D-Dimer is a product of fi brin breakdown and is increased in horses with colic, laminiti s, jugular thrombosis andt D-Dimerother infl is aammatory product of fibrindisorders. breakdown Increased and is increased concentrati in horses withons colic,may thereforelaminitis, jugular give thrombosis an indicati and otheron of inflamma coagulopathy.- D-dimertory disorders. concentrati Increased ons concentrationsin peritoneal may fl thereforeuid may givealso an beindication measured of coagulopathy. as an indicator D-dimer of concentrationsintra-peritoneal in peritoneal fi brinolyti c acti fluidvity may in alsohorses be measured with intesti as an indicator nal disease. of intra-peritoneal In plasma, fibrinolytic concentrati activity in horses ons with above intestinal 1000 disease. ng/ml In plasm area, consideredconcen- to indicate a coagulopathy and in colic cases a concentrati on > 4000 ng/ml is associated with reduced likelihood trations above 1000 ng/ml are considered to indicate a coagulopathy and in colic cases a concentration > 4000 ng/ml is associated of survival. with reduced likelihood of survival. 22 COPYRIGHT © 2015 LIPHOOK EQUINE HOSPITAL. 22 Copyright © 2012 The Liphook Equine Hospital..