Page 498 - Medicine and Surgery

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494 Chapter 12: Haematology and clinical immunology

Aetiology/pathophysiology Clinical features
Mutations on the X chromosome including deletions, The first signs may be bleeding into the tissues partic-
pointmutationsandinsertions.FactorIXisthelastcom- ularly mouth, nose and at venepuncture sites. Patients
ponent of the intrinsic pathway (see Fig. 2.12). are shocked and acutely ill, they develop multi organ
ischaemia and dysfunction.
Clinical features
Similar to haemophilia A with mild deficiency causing Investigations
Coagulation studies reveal prolonged clotting times
onlybleedingpostsurgeryandtrauma.Severedeficiency
and low fibrinogen levels.
presents in early life with recurrent joint and muscle
Fibrinogen degradation products are raised (D-
bleeds.
dimer).
There is thrombocytopenia, blood film reveals frag-

Investigations
mented red blood cells.
Activated partial thromboplastin time is raised, but

correctablewith50%normalserum(i.e.notduetoan
Management
inhibitor of coagulation) other coagulation measures
DIC is managed by treating the underlying cause and
are normal.
blood components using platelets, fresh frozen plasma,
Factor XI levels are low. cryoprecipitate and red cell concentrates. Patients re-

quire supportive care and normally are managed in in-
Management tensive care units.
Treated with factor IX concentrates. Patients who de-
velop antibodies to factor IX concentrates may be suc- Vitamin K deficiency
cessfully treated with recombinant factor VIIa.
Definition
Deficiency of vitamin K, a fat-soluble vitamin, leads to a
Disseminated intravascular bleeding tendency.
coagulation
Aetiology
Definition
Insufficient vitamin K intake or absorption. Sources of
Disseminated intravascular coagulation (DIC) is a gen-
dietary vitamin K include vegetables, peas, beans and
eralised activation of the coagulation system causing
liver. Deficiency occurs in obstructive jaundice and cer-
widespread generation of fibrin within blood vessels and
tain malabsorption syndromes. Warfarin prevents the
consumption of clotting factors.
reduction of vitamin K to its active form leading to func-
tional vitamin K deficiency.
Aetiology
Causes include Gram −ve and meningococcal sep- Pathophysiology
ticaemia, disseminated malignant disease, haemolytic Vitamin K is a co factor in the synthesis of clotting fac-
transfusion reactions, trauma, burns, surgery and P. fal- tors II (prothrombin), VII, IX and X. In its absence the
ciparum malaria. factors do not have an active binding site and are there-
fore functionally deficient. Vitamin K is also involved in
Pathophysiology producing proteins required for bone calcification.
Widespread activation of intrinsic, extrinsic pathways
and platelet aggregation causes consumption of platelets Clinical features
and clotting factors (a consumptive coagulopathy) re- Patients present with bruising, mucosal bleeding and
sulting in a severe bleeding risk. Fibrin is deposited in haematuria.
small vessels within the brain, kidney and lungs caus-
ing ischaemic damage. Red cells are fragmented during Investigations
passage through occluded vessels causing a micro angio- The prothrombin time and the partial thromboplastin
pathic haemolytic picture. time are prolonged.