Platelets

Question 1

Quantitative platelet disorders

Answer 1

Thrombocytopenia and thrombocytosis

Question 2

Qualitative platelet disorders

Answer 2

Abnormal platelet function

Question 3

Thrombocytopenia

Answer 3

A disorder in which there is a relative decrease of platelets present in blood, normal count is 150,000 to 450,000 platelets per microliter

Question 4

Clinical features of thrombocytopenia

Answer 4

Easy bruising, petechiae, prolonged bleeding, bleeding from gums or nose, blood in urine and stools, heavy menstrual flows, fatigue, enlarged spleen, jaundice

Question 5

Lab tests for abnormal bleeding

Answer 5

Platelet count, PT, APPT, bleeding test

Question 6

Thrombocytopenia causes

Answer 6

Decreased production, increased destruction, sequestration, pseudothrombocytopenia, dilutional thrombocytopenia

Question 7

Pseudothrombocytopenia

Answer 7

Artifactually low platelet count due to in vitro clumping of platelets, usually caused by antibodies that bind platelets only in presence of EDTA, seen in healthy individuals and in many disease states

Question 8

Diagnosis of pseduothrombocytopenia

Answer 8

Marked fluctuations in platelet count, thrombocytopenia disproportionate to symptoms, clumped platelets on smear, Platelet satellites, abnormal platelet/leukocyte histograms, platelet count varies with different anticoagulants

Question 9

Platelet satellitism

Answer 9

IgG antibody coats platelets, platelets rosette around segs, bands, and sometimes monocytes, if huddled around WBCs, not counted by automation, causing false decrease

Question 10

Dilutional thrombocytopenia

Answer 10

Large quantities of PRBC transfusion to treat massive hemorrhage can lead to dilution TP, due to absence of viable platelets in packed RBCs, usually platelet counts in patients receiving 15 to 20 units of PRBCs in 24 hours in 50k to 100k, can be prevented by giving platelets

Question 11

Decreased platelet production

Answer 11

Marrow failure, B-12, folate or iron deficiency, viral infection, drugs, amegakaryocytic thrombocytopenia, cyclic thrombocytopenia, inherited thrombocytopenia

Question 12

Thrombocytopenia and ppregnancy

Answer 12

Benign thrombocytopenia of pregnancy, occurs in 5% of term pregnancies, accounts for ~ 75% of cases of thrombocytopenia, asymptomatic, mild, occurs late in gestation, microangiopathy, ITP

Question 13

Increased platelet consumption

Answer 13

Immune destruction, non-immune destruction

Question 14

Non-immune mechanisms of destruction

Answer 14

Disseminated intravascular coagulation, thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, mechanical destruction by artificial heart valves

Question 15

Immune platelet destruction

Answer 15

Autoimmune (ITP), drug-induced (heparin, Quinine), Immune complex (infection), Alloimmune (post-transfusion purpura, neonatal purpura)

Question 16

Post-transfusion purpura

Answer 16

caused by re-exposure to foreign platelet antigen via blood transfusion, almost all cases in multiparous women, antibodies cause destruction of patient’s own platelets by uncertain mechanism, typically presents as sudden onset of severe thrombocytopenia 5-7 days after transfusion

Question 17

Neonatal alloimmune thrombocytopenia

Answer 17

Maternal alloantibodies against a platelet antigen (HPA 1a and 1b), symptoms appear at or shortly after birth and are self limited, rarely high mortality due to CNS bleeding

Question 18

Thrombocytopenia and infection

Answer 18

Immune complex-mediated platelet destruction, activation of coag cascade, vascular/endothelial cell damage, damage to platelet membrane components by bacterial enzymes, decreased platelet production, mixed production defect/immune consumption

Question 19

ITP childhood form

Answer 19

most < 10 years old), may follow viral infection or vaccination, peak incidence in fall and winter, ~50% receive some treatment, >75% in remission within 6 months

Question 20

ITP adult form

Answer 20

No prodrome, chronic, recurrences common, spontaneous remission rate ~5%

Question 21

ITP adult apidemiology

Answer 21

1-10/100,000, slightly more common in women, about 40% have an associated disorder

Question 22

ITP peak age

Answer 22

Children: 2-4 years
Adults: 20-40 years

Question 23

ITP platelet count

Answer 23

Acute: <20 x 10^9/L
Chronic: 30-80 x 10^9/L

Question 24

ITP Onset

Answer 24

Acute: Abrupt
Chronic: Insidious

Question 25

ITP antecedent infection

Answer 25

Acute: Common - 1-3 weeks Chronic: Unusual

Question 26

ITP spontaneous remission

Answer 26

Acute: ~93% Chronic: Rare, course of disease fluctuates

Question 27

ITP therapy

Answer 27

Acute: corticosteroids, Anti-D, IVIg Chronic: Corticosteroids, splenectomy

Question 28

ITP management in children

Answer 28

Platelets > 20-30K, no bleeding = no Rx Platelets <10K or <20K with significant bleeding = IVIg or corticosteroids Splenectomy reserved from chronic ITP or refractory disease with life-threatening bleeding

Question 29

ITP in pregnancy

Answer 29

Mild cases are indistinguishable from gestational thrombocytopenia, rule out eclampsia, treatment if IVIg, splenectomy for severe, refractory disease, potential for neonatal thrombocytopenia

Question 30

Thrombotic microangiopathies

Answer 30

Presence of hemolytic anemia, low platelets, and organ damage due to formation of microscopic blood clots in capillaries and small arteries

Question 31

Thrombotic microangiopathies causes

Answer 31

infection, medications, connective tissue diseases, cancer, vasculitis, pregnancy, malignant hypertension, organ transplant, and metabolic disorders

Question 32

Thrombotic thrombocytopenic purpura presentation

Answer 32

abdominal pain, nausea, vomiting, weakness, 1/2 will have neurologic abnormalities

Question 33

The pentad for TTP

Answer 33

Microangiopathic hemolytic anemia, thrombocytopenia often with purpura, acute renal insufficiency, neurologic abnormalities, fever

Question 34

Causes of TTP

Answer 34

Idiopathic, drug-associated, autoimmune disease, infection, pregnancy/postpartum, bloody diarrhea prodrome, hematopoietic cell transplantation

Question 35

ADAMTS13 deficiency

Answer 35

VWF-cleaving protease, normally cleaves long VWF multimers secreted by endothelial cells, without ADAMTS13, long stick VWF multimers accumulate, react with platelets and cause formation of disseminated platelet thrombi

Question 36

Testing for ADAMTS13 deficiency

Answer 36

Assay techniques, severe deficiency predicts an increased rick of relapse

Question 37

Testing for ADAMTS13 deficiency

Answer 37

Assay techniques, severe deficiency predicts an increased risk of relapse

Question 38

HUS symptoms

Answer 38

Diarrhea, vomiting, urine output reduction, neurologic symptoms, typically follows GI infection

Question 39

Disseminated intravascular coagulation (DIC) causes

Answer 39

Excess tissue factor and endothelial damage, activation of fibrinolysis, other procoagulant or profibrinolytic substances

Question 40

Complications of DIC

Answer 40

bleeding, thrombosis, tissue necrosis

Question 41

Causes of bleeding in DIC

Answer 41

Clotting factor consumption, high levels of FDP, endothelial damage, increased fibrinolytic activity

Question 42

Thrombosis in DIC

Answer 42

Large vessel thrombosis is uncommon, more common in chronic DIC, clots may form around intravascular catheters

Question 43

Contributing factors of tissue necrosis and DIC

Answer 43

intravascular fibrin, endothelial damage, downregulated fibrinolysis, hypotension, pressor administration, acquired protein C deficiency

Question 44

Protein C

Answer 44

Physiological anticoagulant, Vitamin K dependent, destroys factors Va and VIIIa, activated by thrombin bound to endothelium, protective effect on endothelium, severe deficiency of protein C can cause tissue necrosis

Question 45

Protein C

Answer 45

Physiological anticoagulant, Vitamin K dependent, destroys factors Va and VIIIa, activated by thrombin bound to endothelium, protective effect on endothelium, severe deficiency of protein C can cause tissue necrosis

Question 46

DIC summary

Answer 46

Excess tissue factor + flowing blood = DIC, inflammatory cytokines set the stage for DIC and contribute to tissue damage, excessive fibrinolysis associated with higher bleeding risk, acquired protein C deficiency associated with high risk of tissue necrosis/purpura

Question 46

DIC summary

Answer 46

Excess tissue factor + flowing blood = DIC, inflammatory cytokines set the stage for DIC and contribute to tissue damage, excessive fibrinolysis associated with higher bleeding risk, acquired protein C deficiency associated with high risk of tissue necrosis.purpura

Question 47

Diagnosis of DIC

Answer 47

Platelet count, increased fibrinogen degradation products

Question 48

Thrombocytosis cause essential

Answer 48

primary, other myeloproliferative disorders

Question 49

Thrombocytosis cause reactive

Answer 49

Secondary, inflammation, surgery, hyposplenism, asplenia, hemorrhage and/or iron deficiency

Question 50

Criteria for essential thrombocytosis

Answer 50

Platelet > 450K, megakaryocytic proliferation with large, mature morphology and with little granulocytic or erythroid expansion, not meeting other myeloid criteria, demonstration of JAK2V617F or other clonal marker or lack of evidence of a secondary