Coagulation Missed Questions Flashcards
Which vWD causes platelet aggregation and
thrombocytopenia in response to DDAVP ?
- Type 2B
- Gain of function that causes it to bind to GP IB/V/IX more readily
- usually a transient thrombocytopenia that does not cause bleeding or thrombosis
What is the main defect in vWD type 2A ?
- mutation in the vWF protease cleavage site
- leads to increased enzymatic cleavage
- lack of high and intermediate vWF multimers
What is the main defect in vWD type 2M ?
- caused by a loss of function mutation in the vWF binding site on GP IB/V/IX
- leads to decreased binding of vWF to platelets
What is the defect in vWD type 2N?
- mutation in the factor VIII binding site on vWF
What is the mechanism of HIT ?
- antibodies to platelet factor four complexed to Heparin occur
- antibodies can form in response to unfractionated heparin and LMW Heparin, although less likely because of the smaller molecule size
- generally presents as an unexplained thrombocytopenia 4-14 days after heparin administration
What is a Latex Immunoassay used for
in coagulation testing ?
- used for the quantitative detection of plasma proteins
- Process:
- latex is sensitized with reactant and the specimen
- provides a quantitative measurement by using light detection methods or turbidimetry (light absorption) or nephelometry (light scattering) to detect resultant antibody-antigen complexes
- IMP:
- this test does NOT measure activity levels
What is a chromogenic assay used for ?
- it is a qualitative assay, meaning it checks function
- it is a good first step in evaluation of bleeding when there is normal PT, aPTT, and fibrinogen levels
- how do the assays work:
- chromogenic assays provide all components of the coagulation cascade needed to clot except for the factor being measured
- the end point is cleavage of synthetic substrate thorugh enzymatic reaction
- this is determined colorimetrically
- the assay precisely measures the activity of the protein being tested
What sort of coagulation issue should be suspected in a newborn with
bleeding (post circumcision etc) with normal PT, aPTT, and fibriongen levels?
- Factor XIII functional deficiency or less likely quantitative deficiency
How is PCR used in coagulation testing ?
- it is NOT used to measure activity or levels of coagulation factors
How does a clotting assay work in coagulation testing ?
- these are modified PT and aPTT designed to make the factor of interest the rate-limiting step
- How it works:
- test plasma is compared with control plasma
- the amount of correction is then measured
- clot based assays give a broader view of the factor of interest function
- IMP
- activity of factor XIII cannot be detected by clot-based methods
- Clot stability is assessed through the use of 5M of urea or 1% monochloracetic acid
How does an ELISA assay work
in coagulation testing ?
- measures quantitative levels of plasma proteins
- fluorescent labeled antibody is combined with the patient sample, then a labeled detection antibody is added
- the level of fluorescence, luminscence or optical density is then measured to provide an accurate level of the protein of interest
- IMP
- this test does not measure activity levels
What are the different type of factor defects ?
- Type I: quantitative with reduced or absent amounts of factor
- Type II: qualitative with decreased activity despite normal numbers
- Acquired defects can behave as type I or II
- IMP
- when choose a PT or aPTT clot based assay vs. chromogenic assay remember levels of other proteins can affect the clot based assay results while chromogenic is not affected
What can be a cause of Heparin resistance ?
- AT deficiency
- inherited or acquired
- AT deficiency affects Heparin therapy because heparin is not able to accelerate AT effectively if AT is present in low amounts
Which factors are inactivated by Heparin binding to Antithrombin ?
- IIa (thrombin)
- IXa
- Xa
- XIa
Note: aPTT is usually used to monitor UFH therapy. If 25,000 to 35,000 IU of Heparin is administered in a 24 hour period without much affect on aPTT, then resistance should be considered.
IMP: if anti-Xa is elevated out of proportion to the measured aPTT then Heparin resistance should be considered
What are common causes for Heparin resistance ?
- elevated factor VIII activity (acute phase reactant)
- congenital or acquired AT deficiency
- increased Heparin clearance
- increased Heparin binding to proteins
What is the treatment for Heparin resistance ?
- switching to alternative anticoagulant
- Argatroban
- also can administer AT through infusion of plasma or AT concentrates
- monitoring with anti-Xa activity instead of aPTT
What is the function of Heparin cofactor II?
- heparin cofactor II binds to Heparin which leads to inactivation of factor IIa
- increased cofactor activity does NOT cause heparin resistance
Which hemoglobinopathies are associated with
sickling of the peripheral blood ?
- SS
- SC
- SD
- SO
- S/Beta Thalassemia
Note: Hb SG-Philadelphia behaves like a sickle cell trait.
Note: sickle cells are irreversibly damaged red cells. Boat cells are reversibly distorted and resume their discoid shape with oxygenation.
What is the treatment for acquired Factor X deficiency
due to systemic amyloidosis ?
- FFP or prothrombin complex concentrates
- Acquired Factor X deficiency can be seen in:
- vitamin K deficiency or liver disease
- but in these instances it is usually not isolated (II, VII, IX, etc)
- respiratory infections
- thymoma
- malignancies (RCC, adrenal adenocarcinoma, AML)
- aquired inhibitors or congenital deficiencies are rare
- vitamin K deficiency or liver disease
What does microhematocrit measure and how ?
- determines the PCV (percentage of red cells in whole blood) using a potassium EDTA whole blood sample
- how it works:
- a small volume of blood is taken up by the capillary action into a fixed bore capillary tube
- end of the tube is heat sealed and centrifuged for 5-10 minutes at a high rate
- sample separates into red cells, white cells, platelets, and plasma layer
- percentage of the column occupied by red cells (linear distance) compared with the total column is the packed cell volume
What factors affect the microhematocrit PCV ?
- centrifugation time
- centrifugal force
- red cell size and deformability
- increased ESR
- anticoagulant type
- deoxygenation of Hgb
How is the PCV by microhematocrit affected by SS disease, B-Thal,
decreased centrifugation time, increased ESR, and decreased centrifugal force ?
- SS Disease
- PCV is increased by microcytosis, SS disease and other causes of decreased RBC deformability
- B-Thal
- does not affect PCV
- Decreased centrifugation time
- PCV is increased because of excess plasma trapping
- Increased ESR
- causes falsely low PCV due to decreased plasma trapping
- Decreased centrifugal force
- PCV is increased because of incommplete reduction of plasma trapping
What is the inheritance pattern of
Bernard Soulier syndrome and what are the main defects ?
- Autosomal Recessive
- defect in GP Ib/V/IX complex
- Symptoms:
- bleeding
- thrombocytopenia
- large platelets
- bleeding often starts in childhood with frequent nosebleeds, gum bleeding, and easy bruising
How is the diagnosis of Bernard
Soulier made ?
- platelets fail to aggregate with ristocetin
- diagnosis can be confirmed with flow cytometry to analyze GPIb-alpha surface density
What is stored in the Weibel-Palade
bodies of endothelial cells ?
- vWF and P-selectin
- other proteins: IL-8, endothelin, tPA
- Weibel Palade bodies are secretory organelles found within endothelial cells
- they are oval or elongated with a whorled or fingerprint like appearance on EM
- vWF
- acts in primary hemostasis by binding platelets to the subendothelium and also stabilizes factor VIII in plasma
- P-selectin
- participates in leukocyte adhesion
Which is the preferred anticoagulant for a
CBC specimen ?
- K2EDTA
- Note:
- K3-EDTA can cause cell shrinkage and a slight dilution of the sample
- Na-Heparin: causes white cell clumping
- Na-Citrate: dilutes the blood sample and can also cause cell shrinkage
IMP: cell shrinkage causes a lower MCV and HCT
When diagnosing antiphospholipid antibody
syndrome what must be demonstrated ?
- antiphospholipid antibodies must be detected on two or more occasionas at least 12 weeks apart
- this is an acquired autoimmune condition
- symptoms include:
- thrombosis
- microvascular thrombosis usually manifest as catastrophic APS syndrome
- pregnancy loss
- persistent APS antibodies
- thrombosis
What are the clinical criteria for
APS Syndrome ?
- vascular thrombosis: one or more episodes of venous, arterial or small vessel
- pregnancy morbidity
- one or more unexplained deaths of normal fetus at or. >10 weeks
- one or more preterm births of normal neonate before 34th week of gestation due to eclampsia or pre-eclampsia
- 3 or more unexpalined consecutive spontaneous miscarriages before 10th week with other possible causes excluded (hormonal, chromosomal etc)
What are the laboratory criteria
for APS Syndrome ?
- LAC present in plasma on 2 or more occasions, 12 weeks apart of IgG or IgM isotype present at medium or high titer
- Anti-B2 glycoprotein 1 antibody of IgG or IgM isotype in serum or plasma on 2 or more occasions at least 12 weeks apart
- Prolongation of Phospholipid dependent tests on 2 or more occasions
- Demonstration of presence of an inhibitor
- Demonstration of the phospholipid dependence inhibitor
Note: LAC activity is an in vitro phenomenon that is prolongation of phospholipid dependent coagulation tests and not a specific inhibitor to coagulations factors
What are phsopholipid based tests that
can be used to test for LAC antibodies ?
- should always use two or more tests when testing for APS
- Tests
- low phospholipid concentration PTT
- dilute Russell viper venom time
- kaolin clotting time
- dilute PT
- Confirmator testing
- use a high phospholipid concentration test or LAC-insensitiv test to demonstrate phospholipid dependence
What test is used to look for
aCL and anti-B2-glycoprotein antibodies ?
- ELISAS
What lab findings can suggest an
alpha thalassemia trait ?
- presence of microcytosis
- normal hemoglobin fractions (normal A2 and F)
- normal iron studies (may be denoted by normal platelets and Ferritin levels)
Note: alpha thalassemias are most commonly caused by deletion of 1 or more alpha globin genes
How does delta-B Thalassemia present
with lab findings ?
- microcytosis by MCV
- elevated Hgb F
- normal Hgb A2
How does Hgb E trat present in the lab ?
- Microcytosis
- there is peak that elutes on HPLC in the A2 window
IMP: Hgb Lepore also presents in this way on HPLC
How does B-Thalassemia trait present
by HPLC ?
- microcytosis
- elevated Hgb A2
What are the percentages of hemoglobins by HPLC
for Sickle cell trait and S/B Thalassemia ?
- Sickle cell trait:
- Hgb A. > Hgb S fraction
- S/B Thal
- Hgb S > Hgb A
What are antifibrinolytic medications ?
- aminocaproic acid
- aprotinin
- tranexamic acid
What are Howell Jolly Bodies composed of. ?
- DNA
- think …..DNA is long and complex just like the name Howell Jolly Body
What is the size and distribution of the RBCs
on the RBC histogram in treated B 12 def, end stage liver disease,
pseudothrombocytopenia, B-thal trait, and treated Fe def anemia ?
- Treated B12
- macrocytosis
- ESLiver Dz
- macrocytosis
- Pseudothrombocytopenia
- platelet clumps are small and should not have a large distribution of microcytic cells
- B Thal trait
- uniformly distributed microcytic cells
- Fe Def anemia
- variable distribution with microcytes and the macrocytes represent reticulocytes that are being pushed out
What is the Coulter method for detection of
cells in the hematology analyzer ?
- electrical-impedence method
- cells are suspended in an electrolyte solution and passed through an aperture with an electrical field around it
- measures numbers of cells as well as size
- size is X axis, number of cells is Y axis
- IMP
- a dimorphic red cell histogram corresponds to two RBC populations
- dimorphic RBC s can represent treated Fe deficiency anemia, transfused RBCs, treated megaloblastic anemia, sideroblastic anemia, hemolytic anemias
What is the advantage of the red cell histograms ?
- the MCV may be normal in the presence of dimorphic red cell populations
How are Fe deficiency anemia and B-Thalassemia
differentiated on a RBC cytogram ?
- B thal trait
- microcytosis (downward shift) but the hemoglobin content per cell does not decreased
- Fe Def Anemia
- microcytosis and decreased hemoglobin content (leftward shift)
Note: sickle cell disease is usually normochromic, normocytic anemia
What are some general considerations with
Factor V Leiden ?
- inherited thrombophilia disorder with increased risk of VTE
- mutation of Factor V at 1691 G* APC is 10x slower at inactivating FVL than WT
- most common genetic risk factor for VTE, ~5% of caucasians
