Chapter 140 - Disorders of Platelets and Vessel Wall Flashcards
“Genetic and acquired influences on the platelet and vessel wall, as well as on the coagulation and fibrinolytic systems, determine whether normal hemostasis or bleeding or clotting symptoms will result.”
True or False?
True.
Which hormone is the major regulator of platelet production?
Thrombopoietin (TPO).
How much mass of the platelets reside within the spleen? How low can be the platelet count due to an enlarged spleen?
“Approximately one-third of the platelets reside in the simple, and this number increases in proportion to splenic size, although the platelet count rarely decreases to less than 40 000/uL”
Von Willebrand Factor (vWF) is exposed in the subendothelium when there is damage to the vessel wall but there is also plasmatic vWF.
True or False?
True.
What are the major components of the platelet granules?
“Activated platelets undergo release of their granule contents, which include nucleotides, adhesive proteins, growth factors, and procoagulantes that serve to promote platelet aggregation and blood clot formation and influence the environment of the forming clot.”
How many endothelial cells do we have in our circunlatory tree?
1-6 x 10 to the 13, which is “enough to cover a surface area equivalent to about six tennis courts.”
Name the primary vasodilator and vasoconstrictor secreted by the endothelium and name, if applicable, their hemostatic functions.
Nitric oxid is secreted by the endothelium and is the most important vasodilatador which also functions as a platelet inhibitor. Conversely, endothelin is the major vasocontritor secreted by the endothelium which also functions as a platelet activator.
What are the 3 major processes that lead to thrombocytopenia?
“(1) decreased bone marrow production; (2) sequestration, usually in an aenlarged sleen; and/or (3) increased platelet destruction.”
What is the explanation for pseudothrombocytopenia and how can you differentiate from true thrombocytopenia?
“Pseudothrombocytopenia is an in vitro artifact resulting from platelet agglutination via antibodies (usually IgG, but also IgM and IgA) when the calcium content is decreased by blood collection in ethylenediamine tetraacetic (EDTA) (…) If a low platelet count is obtained in EDTA-anticoagulated blood, a blood smear should be evaluated and a platelet count determined in blood collected into sodium citrate (blue top tube) or heparin (green top tube), or a smear of freshly obtained unanticoagulated blood, such as from a finger stick, can be examined.”
The blood smear will reveal platelet clumping in pseudothrombocytopenia.
What is the first step in evaluating a patient with thrombocytopenia?
It is fundamental to evaluate the hemoglobin and white blood count. “Except in unusual inherited disorders, decreased platelet production usually results from bone marrow disorders that also affect red blood cell (RBC) and/or white blood cell (WBC) production).”
In a patient older than 60 year old of age that presents with isolated thrombocytopenia, what might be an important evaluation?
“Because myelodysplasia can present with isolated thrombocytopenia, the bone marrow should be examined in patients presenting with isolated thrombocytopenia who are older than 60 years of age.”
What is the most sensitive bedside technic that can evaluate splenomegaly?
Abdominal ultrassonography.
Name three important findings in patients with thrombocytopenia that denote an increased risk of life-threatening hemorrhage.
Wet purpura, blood blisters and retinal hemorrhage.
How different might be the cell blood count in a patient with early versus late HIV infection?
A patient with early HIV might present with isolated thrombocytopenia. On the other hand, late HIV presents with pancytopenia (anemia is almost always present) and the platelets are dysplatic.
When is it that invasive testing in HIV-infected patients with fever of unknown origin are recommended?
“a bone marrow examination and culture are recommended when the diagnosis is needed urgently or when other, less invasive methods have been unsuccessful.”
Which group of drugs induce thrombocytopenia in a dose-dependent manner?
Chemotherapeutic drugs in general, for example.
What are the most frequent drugs that can induce classsic drug-dependent antibodies?
Quinine and Sulfonamides.
How different in timing is the thrombocytopenia induced by classic drug-dependent antibodies, abciximab and heparin?
Classic drug-dependent antibodies lead to thrombocytopenia after a period of initial exposure with a median of 21 days, resolving 7-10 days after drug withdrawal. Abciximab might induce thrombocytopenia within 24 h of initial exposure. Heparin-induced thrombocytopenia (HIT) might occur affter exposure to heparin for 5-14 days, occuring before 5 days in those who were exposed in the last ~100 days and occuring rarely after 14 days as a form of delayed-onset HIT.
What is the difference between ELISA and platelet activation assay in the study of heparin-induced thrombocytopenia?
ELISA is more sensitive but less specific, namely because it detects the antibodies anti-heparin/PF4), which might occur in asymptomatic patients. The platelet activation assay is more specific but less sensitive since it measures the ability of the patient’s serum to activate platelets in the presence of heparin.
What is the major consequence of heparin-induced thrombocytopenia?
Thrombosis.
