thrombocytopenia
Table of Contents
thrombocytopenia
see also:
- artefectual results are common, and unexpected significantly low platelet counts should be re-checked
- be alert to the possibility of TTP or heparin-induced thrombocytopenia, as a delay in diagnosis can result in serious morbidity or mortality
- patients with counts < 20,000 or those having surgery may warrant platelet transfusion
introduction
- thrombocytopenia is defined by an excessively low concentration of platelets in the peripheral blood < 150 x 10^9/L
- platelets are formed by fragmentation of megakaryocytes, most of which occurs in the lungs and not the bone marrow as was thought 1) and circulate in the blood for 7-10 days
- bleeding time is generally not prolonged until the platelet count is below 100,000/µL
- platelet counts from 20,000/µL to 50,000/µL, petechiae and ecchymoses are observed following mild trauma
- platelet counts below 20,000/µL pose significant risks of major spontaneous haemorrhage
- platelet counts below 10,000/µL, the risk of spontaneous mucocutaneous bleeding (gingival bleed, epistaxis, menorrhagia, petechiae and ecchymoses) and life threatening, spontaneous intracranial haemorrhage or gastrointestinal bleeding increases rapidly
- the risk of bleeding is also dependent upon presence of functional platelet defects
aetiology
- artefactual or pseudothrombocytopenia
- accounts for ~15% of cases in ambulatory patients
- this is caused by in vitro clumping of platelets when ethylenediaminetetraacetic acid (EDTA) is used as an anticoagulant
- dilutional
- 5% of the normal population will fall outside the “normal range” by definition
increased destruction
-
- counts rarely fall below 40,000/µL
- immune-mediated:
-
- esp. well young women
- acute
- chronic
- Evans syndrome: ITP with autoimmune haemolytic anaemia
- heparin-induced thrombocytopenia (HIT)
- Type 1 HIT is a modest transient decrease in platelet counts that occurs within the first 2 to 3 days after heparin initiation and returns to normal spontaneously, even with continuation of heparin
- Type 2 HIT is less common, seen in about 0.3 to 5% of patients caused by antibodies against platelet factor 4-heparin complex, usually occurs 4 to 14 days after heparin initiation. Abnormal thrombosis, sometimes catastrophic, is the predominant manifestation of HIT and bleeding is uncommon. Cease heparin and do not use LMW heparin. - see also thrombosis with thrombocytopenia syndrome (TTS / VITT / VIPIT)
- drug-induced antibodies
- GPIIb/IIIa inhibitor related
- unlike other drug-induced thrombocytopenias, GPIIb/IIIa inhibitor-induced thrombocytopenia develops within 24 hours of exposure
- post-transfusion purpura
- rare, mostly in women, it presents as severe thrombocytopenia 5 to 10 days after red cells or platelet transfusion
- HELLP in pregnant patients
- gestational thrombocytopenia occurs in 5% near delivery
-
- connective tissue (CT) disorders such as systemic lupus erythematosus (SLE), rheumatoid arthritis and antiphospholipid antibody disorder
- non-immune:
- cardiac valves
-
- also have microangiopathic hemolytic anemia (schistocytes, elevated LDH, and indirect hyperbilirubinemia)
- may also have neurologic abnormalities, fever, and renal disease
- may be related to clopidogrel or ticlopidine
- caused by deficiency (due to autoantibodies) of von Willebrand factor-cleaving protease known as ADAMTS13 leads to accumulation of large multimers of von Willebrand factor which cause spontaneous platelet aggregation and thrombi
- emergent plasma exchange is the cornerstone of TTP treatment
- Kasabach Merrit syndrome
decreased production
- haematologic malignancies
- aplastic anaemia
- myelodysplasia
- drugs:
-
- with most chemotherapy agents, nadir blood count occurs 7 to 10 days after chemotherapy and recovery over 2 to 3 weeks
- certain agents like mitomycin can also cause TTP
-
- EBV / glandular fever / infectious mononucleosis, cytomegalovirus (CMV), varicella-zoster virus (chickenpox/shingles), mumps, rubella, parvovirus
- rare infections such as:
- vitamin D deficiencies
- folate deficiency
- hereditary thrombocytopenias
- Congenital amegakaryocytic thrombocytopenia
- Thrombocytopenia absent radius syndrome
- Fanconi anemia
- Bernard-Soulier syndrome, associated with large platelets
- May-Hegglin anomaly, the combination of thrombocytopenia, pale-blue leuckocyte inclusions, and giant platelets
- Grey platelet syndrome
- Alport syndrome
- Wiskott–Aldrich syndrome
- metastatic tumours to bone marrow
Mx of incidental thrombocytopenia
- exclude artefactual cause ⇒ repeat full blood examination (FBE)
- if within 4-20 days of an Astra-Zeneca Covid-19 vaccine then investigate for possible thrombosis with thrombocytopenia syndrome (TTS / VITT / VIPIT)
- if neutropenia and/or anaemia as well then ?aplastic anaemia
- is patient pregnant?
- LFT's ⇒ ?HELPP vs gestational vs ITP
- history - PH ITP, drugs, heparin, chemotherapy, cancer, etc.
- examination - evidence of bleeding, splenomegaly,
- if febrile, search for underlying illness eg. sepsis, TTP, viral infections, typhoid, etc
- check full blood examination (FBE) smear:
- platelet clumps ⇒ artefactual
- giant platelets ⇒ hereditary thrombocytopenia
- schistocytes or spherocytes ⇒ look for haemolysis (LDH, bilirubin) and if confirmed:
- Direct Coombs
- +ve: Evans syndrome
- -ve: check for disseminated intravascular coagulation (DIC), if negative then ?thrombotic thrombocytopenic purpura (TTP)
- suspicious smear for primary marrow disorder ⇒ bone marrow Bx
- nucleated red cells
- bilobed neutrophils
- macrocytosis
- blasts
- isolated thrombocytopenia
- ?chemotherapy-induced
- ?drug-induced (eg. heparin) ⇒ cease drug and platelet count should recover in 5-7days
- consider bone marrow biopsy
indications for platelet transfusion
- platelet count < 10,000/µL
- platelet count < 20,000/µL plus presence of bleeding, fever, infection, platelet function defect, or coagulopathy
- platelet count < 50,000/µL prior to minor procedures, in actively anticoagulated patients or in the presence of active bleeding
- platelet count < 75,000/µL prior to general surgery
- platelet count < 100,000/µL prior to neurologic or ophthalmologic surgery2)
thrombocytopenia.txt · Last modified: 2021/05/10 22:08 by gary1