Thrombocytopenia

-low level of platelets.
-150-400*10^9/L-normal
-purpura and bleeding from mucous membrane when low

-Features according to levels:
 >500-thrombosis or haemorrhages
>500-100-no clinical effect/ manifestation
100-50-moderate clinical manifestationemorrhage after injury
50-20-purpura may occur after injury
<20-purpura(common), sponstanous haemorrhage from mucous membrane, ICH

Causes:
-decreased production
-excessive peripheral destruction
-sequestration in enlarged spleen

Impaired production:
-selective megakaryocyte depression(rare congenital defect, drugs, chemical, viral)
-as a part of general bone marrow failure.
-cytotoxic drugs and chemicals.
-megaloblastic anaemia
-leukaemia
-myelodysplastic syndrome.
-myelofibrosis
-solid tumour of infiltration
-aplastic anemia
-HIV infection

Excessive peripheral destruction:
-Immune-
   autoimmune:
             -autoimmune ITP(-immune -mediated thrombocytopenia purpura)
             -drug induced.-penicillin, thiazide
              systemic immune-sle, chronic lympocytic leukemia
             -alloneonatal thrombocytopenia(genetic differnces between mom and fetus-Ag by fetus-->therefore Mother produces Ab by mother against it)
             -post transfusion purpura(after 5-7 days transfusion)
             -DIC-pathological activation of coagulation pathway in response to different clinical conditions)
             -thrombotic thrombocytic purpura

Excessive Consumption/sequestration
-spleenomegaly
-hyperspleenism(overactive spleen)