Haematology

Question 1

What percentage of cases of neutropenia are suspected to be drug induced?

Answer 1

70%

Question 2

What are some of the main culprit drugs responsible for drug-induced neutropenia?

Answer 2

Antibiotics - Chloramphenicol, Dapsone, Isoniazid, Meropenem, Streptomycin, Sulfamethoxazole-trimethoprim

Antifungals - Terbinafine

Antimalarials - chloroquine, primiquine, quinine

Anti-inflammatories - diclofenac, ibuprofen, sulfasalazine

Anti-thyroid drugs - carbimazole, PTU

Antipsychotic drugs - chlorpromazine, clozapine

Antidepressants - mirtazapine, mianserin, tricyclics

Anti-epileptics - Carbamazepine, Ethosuximide, Phenytoin, Valproate, Zonisamide

Cardiovascular drugs - ACEIs, Acetazolamide, Digoxin, Flecainide, Procainamide, Propranolol, Spironolactone, Ticlopidine

Immunomodulators - hydroxychloroquine, leflunomide, rituximab

Others:
Colchicine
Deferiprone
Metoclopramide
Nitrous oxide
Pirfenidone

Question 3

Chemotherapy-induced neutropenia is often dose-dependent, associated with other cell lines (due to bone marrow toxicity) with the nadir occurring at 7-14 days and recovery over 3-4 weeks - what is unusual about the neutropenia that can occur in patients treated with chemotherapy + Rituximab therapy?

Answer 3

Patients who receive the anti-CD20 monoclonal antibody rituximab in addition to chemotherapy may, rarely, experience a delayed neutropenia beyond this 3-4-week period with unpredictable onset and recovery time

Question 4

Why is it important to differentiate between idiosyncratic drug-induced neutropenia and dose-dependent drug-induced neutropenia?

Answer 4

Because idiosyncratic drug-induced neutropenia is associated with increased rates of infection and mortality rates ranging from 2.5-25%

Question 5

How do you treat drug-induced neutropenia?

Answer 5

Cease the culprit medication immediately in patients with evolving neutropenia or agranulocytosis. However, if the effect is dose-dependent and mild, drugs can sometimes be continued with close monitoring, although making this distinction can be difficult

Question 6

What are the most common infectious-causes of neutropenia?

Answer 6

Viral infections

Short and self-limited:
Viral hepatitis
Viral exanthems (measles, rubella, varicella)
Influenza
Cytomegalovirus
Parvovirus

Prolonged:
HIV
EBV

Question 7

Can neutropenia be secondary to bacterial infection and if so, which ones in particular?

Answer 7

Brucellosis
Mycobacterial infections incl TB
Rickettsial infections
Malaria
Severe overwhelming sepsis - poor prognostic indicator

Question 8

How do you make the diagnosis of autoimmune neutropenia (ie related to autoimmune disease such as RA/SLE)

Answer 8

Largely clinical - as assays for antineutrophil autoantibodies are difficult to perform and generally considered to be unreliable or non-diagnostic

Question 9

What is the significance of autoimmune neutropenia?

Answer 9

Neutropenia can be triggered by a flare in the underlying disease and tends to track disease activity.

Question 10

How do you treat autoimmune neutropenia?

Answer 10

Most cases improve on management of the underlying condition and rarely require specific treatment

Question 11

What is the classic triad of Felty’s syndrome?

Answer 11

RA + neutropenia + splenomegaly

Question 12

What is the significance of recognising Felty’s syndrome?

Answer 12

Neutropenia tends to be severe and is associated with significant morbidity from infective complications and the RA is severe and deforming.

Question 13

How do you treat Felty’s syndrome?

Answer 13

Felty’s syndrome is currently rarely seen because of early and aggressive management as well as substantial advancements in the efficacy of available therapies

Controlling the RA tends to resolve the neutropenia, but G-CSF (filgrastim or pegylated filgrastim) may be necessary in refractory cases

Question 14

What nutritional deficiencies can cause neutropenia?

Answer 14

Vitamin B12 (assoc macrocytic anaemia)
Folate (assoc macrocytic anaemia)
Copper
Global - anorexia nervosa

Question 15

What features may suggest a bone marrow failure/infiltration/dysplasia as cause of neutropenia?

Answer 15

• Other cell lines affected (eg anaemia)
• B symptoms incl fevers, weight loss, night sweats
• lymphadenopathy or bone pain
• blood film abnormalities incl blasts or in solid organ malignancies assoc with marrow involvement -> leukoerythroblastic anaemia (that is, nucleated red cells and neutrophil precursors)

Question 16

What features does T-cell large granular lymphocytic leukaemia (T-LGLL)-associated neutropenia share with Felty’s syndrome?

Answer 16

An association with RA
Splenomegaly
Severe neutropenia
An association with HLA-DR4.

Question 17

How do you differentiate T-cell large granular lymphocytic leukaemia (T-LGLL)-associated neutropenia from Felty’s syndrome?

Answer 17

Monoclonal lymphocytes in T-LGLL
vs
Oligoclonal or polyclonal lymphocytes in Felty’s syndrome

Question 18

How do you diagnose Chronic Idiopathic Neutropenia?

Answer 18

Once you have excluded other causes eg with history and exam + bone marrow biopsy

More common in px with mediterranean ancestry + mild-to-mod neutropenia (rarely dips <0.8 or requires treatment)

Question 19

What is constitutional neutropenia (previously called benign ethnic neutropenia)?

Answer 19

A form of chronic, mild neutropenia in patients of the relevant ethnicity, with no other evident causes

Ethnicities - some Mediterranean, African, Yemenite Jewish, Ethiopian, Middle Eastern, Caribbean and West Indian populations

The diagnosis requires at least three blood tests showing neutropenia at least two weeks apart + exclusion of other causes

Note no associated increased rates of infection

Question 20

What are the core features of cyclic neutropenia (CN)?

Answer 20

Cyclic neutropenia (CN) is a rare condition characterised by self-limiting neutropenia associated with fever, skin or oral ulcers, and/or cervical lymphadenopathy during a neutrophil nadir that occurs every 2-5 weeks

Patients are generally well between episodes

The absolute neutrophil count oscillates and severe neutropenia typically lasts 4-5 days each cycle, during which patients are also prone to infections

Cycle lengths vary between patients but are consistent in an individual

To diagnose CN, serial FBCs are required 2-3 times a week for at least six weeks to establish the pattern of neutropenia

The diagnosis can be confirmed with genetic testing for ELANE gene mutations and does not routinely require a bone marrow biopsy.

CN is an autosomal dominant condition resulting from mutations in the ELANE gene, the same gene implicated in many cases of SCN

Question 21

What initial investigations should be ordered for a patient with neutropenia?

Answer 21

Recommended for all patients:
- FBC with differential.
- Blood film.
- EUC.
- LFTs.

Focused investigations based on clinical assessment:
- Septic screen (including blood culture).
- ANA, dsDNA, RF, anti-CCP, ESR/CRP.
- Flow cytometry
- B12/folate/copper
- HIV, HCV, HBsAg, HBsAb, HBcAb and other viral serology as appropriate.

Specialised investigations considered by a haematologist:
- Bone marrow biopsy.
- Genetic studies.

Question 22

What are the main risks with G-CSF (Filgrastim) therapy

Answer 22

bone pain, myalgias, splenomegaly and osteoporosis

There is also a theoretical increased risk for AML in Severe Congenital Neutropenia

G-CSF is safe in acquired causes of neutropenia with no identified increased risk for AML

Question 23

What are the indications for considering bone marrow transplant in a patient with Cyclic Neutropenia?

Answer 23

Disease refractory to G-CSF, recurrent severe infections, bone marrow failure and malignant transformation

Question 24

What is the most common inherited bleeding disorder?

Answer 24

Von Willebrand Disease

Question 25

What is the mode of inheritance for von Willebrand disease?

Answer 25

Autosomal with variable penetrance and expressivity

Question 26

What is the cause and pathophysiology of von Willebrand Disease?

Answer 26

VWD is due to qualitative and quantitative defects in von willebrand factor secondary to an autosomal genetic condition Rarely patients can develop acquired von Willebrand syndrome secondary to lymphoproliferative disorders (e.g. MGUS, MM, Waldenstrom's) and has been reported with aortic stenosis and hypothyroidism Von Willebrand Factor is synthesised in endothelial cells and megakaryocytes and is a high molecular weight multimer VWF mediates platelet adhesion to exposed subendothelium at sites of vascular injury + stabilises and carries factor VIII (protective co-factor) Patients with vWD predominantly have symptoms of platelet dysfunction eg mucosal bleeding Type 1 = quantititive defect Type 2 = qualitative defect Type 3 = severe quantitative defect

Question 27

What subtypes of von Willebrand disease may be accompanied by haemarthroses and low factor VIII levels?

Answer 27

Type 2N and type 3 - can resemble haemophilia A Type 2N = marked decrease in the affinity of vWF for factorVIII thus patient's factor VIII half life is very short (plasma levels reduced to 5-25%) Type 3 = complete absence of VWF

Question 28

What is unique about Type 2B von Willebrand Disease?

Answer 28

It is actually a result of a gain-of-function mutation which increases binding of vWF to platelets resulting in the platelet-VWF complex being more readily cleaved by ADAMTS13 and subsequently cleared by the reticuloendothelial system These patients often have a mild-to-moderate thrombocytopenia

Question 29

What blood group has lower von Willebrand Factor levels at baseline?

Answer 29

O-type blood

Question 30

Why might a young adult with mucosal bleeding who is diagnosed with von Willebrand's disease have normal von Willebrand Factor levels in later life?

Answer 30

Because von Willebrand Factor levels increase with age and may, in a sizeable % of patients reach normal levels later in life Note vWF levels can increase with exercise, inflammation, stress and menstrual cycle/pregnancy

Question 31

What are the typical symptoms of von Willebrand Disease?

Answer 31

Easy bruising Excessive bleeding from minor wounds/surgery esp mucosal eg tonsillectomy, wisdom tooth extraction Mucosal bleeding Menorrhagia May have symptoms of iron deficiency/anaemia

Question 32

Which subtypes of VWD are associated with more severe disease?

Answer 32

Type 2 or 3 - symptoms may begin at earlier age, more likely to have positive family history (as autosomal dominant) and in cases of type 2N or 3 may have haemarthroses

Question 33

How do you test for von Willebrand Disease?

Answer 33

In addition to FBC and coagulation tests (which are often normal) request: 1) von Willebrand factor antigen (measures the quantity of plasma vWF using ELISA-based method; <30% = VWD, 30-50% with positive bleeding history also indicates VWB) 2) Platelet-dependent VWF activity (eg VWF:RCo or VWF:GP1BM or VWF:CB) - these assess the ability of VWF to bind to its normal binding partners VWF:RCo has been the gold standard but not automated and not as sensitive so VWF:GP1bM/collagen so now others mostly used <30IU = VWD 30-50IU and bleeding history = VWF 3 ) Factor VIII levels (often normal or low-normal but may be frankly decreased in VWD Type 2N or 3)

Question 34

How do you distinguish between VWD and mild haemophilia?

Answer 34

Clinically similar bleeding symptoms although VWD tends to have more mucosal bleeding Family history - VWD is autosomal whilst haemophilia is X-linked pattern Investigations: haemophilia have reduced Factor VIII with normal VWF Ag and activity Type 3 VWD - factor VIII + VWF ag + VWF activity all reduced Type 2N VWD - Use special VWF binding to normal factor VIII studies and/or genetic analysis of the VWF binding site for factor VIII

Question 35

How do you distinguish the subtype of VWD?

Answer 35

Initially can look at platelet-dependent VWF activity to VWF antigen level - if ratio >0.7 = Type 1 - if ratio <0.7 = Type 2 because it demonstrates platelet-dependent VWF activity is out of proportion to reduction of VWF in circulation Can also perform FactorVIII activity to VWF antigen (low in Type 2N) Can also perform VWF multimer analysis (visually quantifies the densitometry of the bands to distinguish those with large multimers from others

Question 36

What other tests might you consider in patient with newly diagnosed von Willebrand Disease?

Answer 36

TSH - to detect hypothyroidism Serum protein electrophoresis - to detect MGUS/MM

Question 37

How do you treat von Willebrand disease?

Answer 37

Depends on subtype Note if life-threatening bleeding - treat as for type 3 until more information required with: VWF-containing concentrate +/- platelet transfusion +/- cryoprecipitate Type 1 - see whether they respond to desmopressin (desmopressin results in release of vWF and Factor VIII from endothelial stores); patients show have at least 3-5x increase in levels of these 30-60mins post administration - antifibronolytics (e.g. tranexamic acid) + desmopressin (if desmopressin responder) OR vWF-containing concentrate (if non-responder) Type 2 - can use desmopressin for 2A and 2M (may respond) + antifibrolytic + VWF containing concentrates - however desmopressin ineffective in 2B (and may worsen thrombocytopenia) and 2N Type 3 - VWF-containing concentrates (note important to give high-purity concentrate which also contains Factor VIII as otherwise takes 6-8hrs post-VWF alone for endogenous levels of Factor VIII to reach haemostatic levels + antifibrinolytic therapy

Question 38

How do you treat patients with chronic or recurrent menorrhagia in setting of vWD?

Answer 38

Hormonal therapy (if benefits > risks) as oestrogen increases VWF and may reduce menstrual blood flow + antifibrinolytics Can consider desmopressin but evidence inconclusive

Question 39

How do you treat patients with chronic or recurrent or treatment refractory bleeding and VWD?

Answer 39

Prophylactic VWF-containing concentrates + haematologist care However note some patients can develop antibodies to VWF after treatment with VWF so you need to monitor levels if repeated administration + ensure factor VIII levels are not excessively elevated due to potential risk of thrombosis

Question 40

What key long-term management issues do you have to consider in patients with VWD?

Answer 40

1) May require intermittent acute treatment for active bleeding throughout their lives 2) May require prophylactic treatment before procedures throughout their lives 3) If become pregnant require high-risk obstetric and haematology care as higher risk incl for delayed/post-natal haemorrhage 4) Can develop antibodies to VWF after repeated administration of VWF-concentrates which reduces effectiveness of VWF-concentrates

Question 41

What is the mode of inheritance for Haemophilia?

Answer 41

X-linked pattern therefore occurs almost exclusively in males

Question 42

Haemophilia A is due to deficiency of which coagulation factor?

Answer 42

Factor VIII

Question 43

Haemophilia B results from the deficiency of which coagulation factor?

Answer 43

Factor IX (9)

Question 44

Are there any other forms of haemophilia?

Answer 44

Yes - there is an acquired/non-inherited haemophilia which is autoimmune-related

Question 45

Why might some women manifest with haemophilia-range clotting factors/bleeding symptoms?

Answer 45

Due to lyonisation (random inactivation of the normal X chromosome) or homozygosity or mosaicism or Turner syndrome

Question 46

What is the pathophysiology of haemophilia?

Answer 46

Genetic defects result in decreased or absent levels of coagulation factor 8 (Haemophilia A) or 9 (Haemophilia B). These are crucial for thrombin generation via the intrinsic pathway. Reduced thrombin generation leads to delayed and unstable clot formation that can be easily dislodged causing excessive bleeding.

Question 47

What is the hallmark form of bleeding in haemophilia?

Answer 47

Musculoskeletal bleeding

Question 48

When are patients typically diagnosed with haemophilia?

Answer 48

As children however some, particularly those with mild or even moderate haemophilia who have had no significant haemostatic challenges in their lives may go undiagnosed until adulthood. Acquired haemophilia is often not recognised or mistake for other acquired bleeding disorders

Question 49

How do you distinguish haemophilia A from haemophilia B?

Answer 49

The are indistinguishable clinically Therefore the only way is on plasma factor VIII and IX assay

Question 50

How do you grade haemophilia?

Answer 50

Into mild, moderate and severe based on factor level <0.01 = severe 0.01-0.05 = moderate 0.05-0.40 = mild

Question 51

What is the effect of emicizumab therapy on APTT/factor VIII levels in patients with haemophilia A?

Answer 51

It will shorten APTT and improve Factor VIII levels - this effect will persist for up to 6 months after discontinuation Note - in the rare case when the development of anti-emicizumab antibodies is suspected, APTT will be inappropriately prolonged (as emicizumab effect is absent)

Question 52

What testing should you order in patients with suspected haemophilia?

Answer 52

1) APTT - typically prolonged (but may not be in mild cases) - typically corrects with mixing - if clinical suspicion or prolonged APTT then order 2) Factor VIII and Factor IX assay 3) FBC - usually normal, may have anaemia if severe bleeding 4) PT - should be normal - if prolonged need to check factor VII and factor V 5) von Willebrand factor assay - to exclude VWD 6) LFTs - to evaluate for liver dysfunction as cause of prolonged PT/aPTT

Question 53

What does correction of aPTT with mixing study suggest?

Answer 53

A mixing study involves incubating patient plasma with normal plasma for 2 hours at 37deg and repeat aPTT If aPTT corrects with a mixing study it suggests a coagulation factor deficiency If aPTT does not correct it suggests the presence or a coagulation inhibitor

Question 54

If aPTT is prolonged (and correct on mixing studies) but factor VIII and factor IX levels are normal, what should you test for?

Answer 54

Factor XI and XII levels

Question 55

What are the key principles of (congenital) haemophilia care?

Answer 55

1) Treatment and prevention of bleeding 2) Rehabilitation after joint and muscle bleeds 3) Prevention and long-term management of joint and muscle damage - incl physiotherapy, joint protection, maintenance of ROM, balance 4) Education 5) Pain management 6) Dental care 7) QOL and psychosocial support 8) Gentetic counselling and diagnosis '

Question 56

What is meant by haemophilia patients having an aura?

Answer 56

Some patients may experience tingling sensation or tightness within the joint the preceeds the appearance of clinical signs of a joint bleed or recognise early signs before obvious bleedinge

Question 57

In patients with haemophilia B, the development of inhibitors is often heralded by what?

Answer 57

Anaphylaxis to factor IX products Thus important to administer in appropriate setting in first 10-20 factor IX exposure days Those who develop anaphylaxis have an increased risk of developing nephrotic syndrome upon factor IX exposure

Question 58

How do you treat acute bleeding in congenital haemophilia (in those without factor inhibitors)?

Answer 58

Factor VIII (Haemophilia A) or factor IX (haemophilia B) concentrate infusion + Antifibrinolytics (eg tranexamic acid) + pain medications + consider desmopressin (in patients with mild haemophilia A and demonstrated positive response to desmopressin) + topical haemostatic agents eg fibrin sealant + PRICE (protection, rest, ice, compression, elevation)

Question 59

How many haemophilia patients develop inhibitors to infused factor concentrates and how do you manage these patients when they present with acute bleeding?

Answer 59

30% of patients with haemophilia A 5% of patients with haemophilia B Treatment in these patients is complex and should be managed in a specialist haemophilia center. Depends on current and historical maximum inhibitor titre (determined by <5 Bethesda unit [low-responder inhibitor] vs >5 [high-responder] Options include: 1) Specific replacement factor at a much higher dose than usual 2) Bypassing agent such as recombinant factor VIIa (MOA: binds activated factor VII to tissue factor which activates factor X and leads to thrombin generation + at supraphysiological concentrations binds the surface of activated platelets activating factor X independent of tissue factor and generating thrombin) OR Factor VIII inhibitor bypassing fraction - contains variable amounts of vit=K dependent clotting factors which generate thrombin by bypassing factor VIII/factor XI in coagulation cascade) However, there is a risk of risk of thrombotic microangiopathy and thrombosis with the use of these - especially in those patients on emicizumab therapy (avoid for up to 6 months after) or with concurrent antifibrinolytic therapy (so don't give)

Question 60

What are the risk factors for development of factor inhibitors in haemophilia patients?

Answer 60

Disease severity - more common in severe haemophilia Environmental - more common early in factor concentrate treatment, ethnicity (higher in african populations), and varies with infection, age, type of production Genetic mutation - people with family history or those with mutations that result in absence of a gene product (e.g. large deletions, nonsense mutations) more likely

Question 61

What are the contraindications to antifibrinolytic agents (e.g. TXA)?

Answer 61

Any haematuria (as unlysed clots will behave like stones causing obstructive nephropathy) Bleeding into the thoracic cavity - an unlysed haematoma may interfere with respiration

Question 62

What treatment may be indicated in haemophilia patients with recurrent bleeds into a target joint?

Answer 62

Radioactive synovectomy (synovioorthesis) - if this fails, may require surgical synovectomy

Question 63

What are the indications and agents for prophylaxis in haemophilia patients?

Answer 63

Severe haemophilia A or B (including those with inhibitors) + those with mild-to-moderate haemophilia with a severe phenotype Primary prophylaxis = when started before age 3 / before clinically detectable joint damage Secondary prophylaxis = therapy initiated after 2 or more joint bleeds but before the onset of joint disease Tertiary prophylaxis = therapy started after development of joint disease Agents: Haemophilia A - factor VIII concentrates OR emicizumab Haemophilia B - factor IX concentrate

Question 64

What is the role of Emicizumab in haemophilia A treatment?

Answer 64

Prophylaxis only in haemophilia A patients with or without inhibitors Cannot be used to treat acute bleeds, cover surgical procedures or haemophilia B prophylaxis

Question 65

How do you treat haemophilia patients with factor inhibitors?

Answer 65

Goal is to eliminate the inhibitor with the use of Immune Tolerance Induction (ITI) This involves high doses of relevant factor concentrate for months to years (usually once a day) If this doesn't work - can try rituximab

Question 66

If you come across a patient with haemophilia who was commenced on treatment in the 1970s, what else do you have to be conscious of?

Answer 66

That they may have contracted HCV / HBV or HIV from blood products 70-90% of those treated in 1970s-80s contracted blood-borne diseases (ie before certain measures were instituted)

Question 67

What are more common - Group 1 or Group 2 inherited thrombophilias?

Answer 67

Group 2 eg factor V Leiden, prothrombin gene mutation and sickle cell disease Group 1 = reduced level of inhibitors of coagulation cascade Group 2 = increased levels/function of coagulation factors

Question 68

What are the 5 types of Group 1 inherited thrombophilias?

Answer 68

1) Antithrombin deficiency 2) Protein C deficiency 3) Protein S deficiency 4) Plasminogen deficiency 5) Dysfibrinolysis

Question 69

What is the role of antithrombin in coagulation?

Answer 69

AT is a major inhibitor of blood coagulation (ie a natural anticoagulant) - it works by inhibiting the coagulation proteases 2a (thrombin), 10a, 9a and 11a. Following the administration of heparin or fondaparinux, AT activity is accelerated dramatically due to conformational change induced by heparin binding that exposes the reactive center in AT converting AT from a slow inactivator of coagulation factors to a rapid inactivator (1000-fold increase in AT activity) Endogenous heparin sulfates in endothelium likely provide this role in normal physiology therefore localising the inhibitory activity of AT to endothelial surface of blood vessels. The half life of AT is 3-5 days - production (by the liver) and turnover is highly regulated AT deficiency (due to quantitative or qualitative defects in AT) leads to uncontrolled thrombin generation and fibrin deposition within the vasculature leading to increased thrombotic risk +/- insensitivity to heparin

Question 70

What are the causes of antithrombin deficiency?

Answer 70

AT deficiency can be acquired or inherited Acquired = diseases that cause reduced AT levels e.g. - liver disease (primarily cirrhosis) - nephrotic syndrome - acute thrombosis (accelerated consumption) - DIC (consumption) - ECMO - surgery/trauma - asparaginase therapy (for ALL) - heparins - oestrogrens Genetic = autosomal dominant with variable penetrance - heterozygosity for a variant in SERPINC1 gene - note do not see homozygosity for AT deficiency as not compatible with life Resulting phenotypes characterised as type 1 and type 2 deficiency - type 1 = reduced AT level - type 2 = functional deficiency due to pathogenic variants

Question 71

Is antithrombin affected by pregnancy?

Answer 71

No, not in normal pregnancies However AT levels may decrease significantly with pregnancy-induced hypertension, PET or eclampsia Also, patients with AT deficiency appear at particularly high risk of thrombosis during pregnancy

Question 72

Is antithrombin considered an acute phase reactant?

Answer 72

No

Question 73

Can antithrombin function be assessed by routine coagulation tests/ affects coagulation testing?

Answer 73

No - does not affect PT, aPTT or TT

Question 74

When should you test for antithrombin deficiency?

Answer 74

Rarely May test in cases of: - suspected inherited thrombophilia based on family history or atypical presentation - children with thromboembolism in absence of CVC - suspected heparin resistance - asparaginase therapy or ECMO

Question 75

Can you test for antithrombin deficiency at the time of thromboembolic event?

Answer 75

No because thrombosis may cause a transient reduction in AT levels that could be misinterpreted as an underlying inherited deficiency

Question 76

What is the best first test for Antithrombin deficiency?

Answer 76

Antithrombin-heparin cofactor assay It is a functional assay that measures the ability of heparin to inhibit coagulation factor 2a (thrombin) or 10a (more specific) which requires AT activity

Question 77

Why is the functional assay measuring the ability of heparin to inhibit Factor 10a preferred over inhibition of Factor 2a (thrombin) when testing for antithrombin deficiency?

Answer 77

Because factor 10a is inhibited by AT (heparin cofactor 1) alone via a heparin-dependent mechanism whereas thrombin can also be inhibited by a heparin cofactor 2 (thus differences in heparin cofactor 2 activity may affect assay results)

Question 78

What is the lower limit of normal for Antithrombin activity?

Answer 78

80% Most patients with hereditary AT deficiency have levels in the 40-60% range

Question 79

When after a thromboembolic event should you test for antithrombin deficiency if you are going to test for it?

Answer 79

Most times should delay until patient recovers or is no longer receiving an anticoagulant Exceptions: - family members of individuals with AT deficiency for whom rapid diagnosis is important for care eg in setting of emergency surgery - individuals receiving heparin therapy for whom a therapeutic aPTT cannot be achieved and/or additional thrombosis develops and for whom AT replacement therapy or change in anticoagulant might be indicated - individuals receiving asparginase for whom AT replacement would be indicated if AT deficiency diagnosed Note, if patient on direct Xa inhibitor (eg rivaroxaban) can test thrombin-based assay; if patient on direct thrombin-inhibitor (eg dabigatran) can test factor Xa-based assay Warfarin does not affect antithrombin levels

Question 80

Is genetic testing necessary for diagnosing antithrombin deficiency?

Answer 80

No, not routinely ordered Demonstration of SERPINC1 mutation is confirmatory but not required However do have to exclude acquired causes

Question 81

How does the presence of antithrombin deficiency alter management for VTE?

Answer 81

- Often requires indefinite anticoagulation - Preference for initial parenteral anticoagulation especially for severe thromboses - Slight preference for warfarin over DOAC given more data and clinical experience plus able to monitor anticoagulant effect (using INR) and establish if people taking anticoagulant/was in target INR range if have recurrent event (note this is important as some patients with AT deficiency are extremely thrombosis-prone and sustain recurrent VTE events despite therapeutic anticoagulation)

Question 82

When might you use antithrombin replacement?

Answer 82

In some cases of AT deficiency with unusually severe thrombosis, recurrent thrombosis despite adequate anticoagulation or heparin resistance (especially those on ECMO, undergoing cardiopulmonary bypass surgery or on dialysis)

Question 83

What other long-term management considerations are there for patients with antithrombin deficiency?

Answer 83

- Avoid estrogen containing contraceptives - Thromboprophylaxis during pregnancy (usually with LMWH) - Monitor AT levels during asparaginase therapy and provide LMWH thromboprophylaxis

Question 84

What is the most common site of asparaginase-associated thrombosis?

Answer 84

Intracranial eg dural sinus thrombosis (Therefore consider if headache, focal neurologic findings or encephalopathy when on asparaginase-chemotherapy)

Question 85

What is the cause of Factor V Leiden (FVL)?

Answer 85

A point mutation F5 gene which encodes the factor V protein in the coagulation cascade Factor V is a procoagulant that circulates in its inactive form in plasma - at the site of tissue injury, a small amount of thrombin activates factor V which then serves as a cofactor in the prothrombinase complex which cleaves prothrombin to generate more thrombin - that is, it amplifies the production of thrombin (which converts fibrinogen to fibrin leading to clot formation) Meanwhile, thrombin also slows its production by creating a separate negative feedback loop by converting protein C to activated protein C which degrades factor Va and VIIIa reducing thrombin production (note aPC uses free protein S as a cofactor in these reactions) The single point mutation in F5 (replacement of arginine with glutamine at amono acid 506) renders both active and inactive forms of Factor V insensitive to the actions of activated protein C (aPC) by abolishing the Arg506 cleavage site for aPC This means FVL increases clotting by 2 changes: 1) activated FVL (procoagulant) cannot be cleaved by aPC 2) unactivated FVL (anticoagulant) cannot act as effective cofactor for aPC resulting in reduced degradation of FVa and FVIIIa Therefore, FVL increases the risk of VTE

Question 86

What is the mode of inheritance of FVL?

Answer 86

Autosomal dominant 99% are heterozygous for the variant 1% homozygous or pseudo-homozygous - disproportionate risk of VTE

Question 87

What percentage of FVL heterozygotes will experience VTE during their lifetime?

Answer 87

5-10%

Question 88

What is the FVL paradox?

Answer 88

The occurrence of isolated PE (ie without evidence of DVT) in individuals with FVL is less common than individuals without FVL

Question 89

When should you suspect FVL?

Answer 89

- in someone with positive family history - individual with VTE at young age <50 - individual with VTE in unusual location eg portal vein, cerebral vein - individual with recurrent VTE

Question 90

What test should you order to diagnose FVL?

Answer 90

Genetic test - if positive family history - if antiphospholipid syndrome - if receiving anticoagulant that might interfere with results - if positive functional assay (Genetic testing can be done on peripheral blood, fairly straightforward and inexpensive and is unaffected by anticoagulants BUT it will not detect other hereditary causes of aPC resistance or acquired causes of aPC resistance) Functional aPC resistance assays (2nd generation) - first line for individuals not fitting above (cheaper than genetic testing HOWEVER may be falsely abnormal if lupus anticoagulant present or falsely normal if taking DTI (dabigtran) or Xa inhibitor (apixaban etc)

Question 91

What non-VTE conditions are associated with FVL?

Answer 91

Osteonecrosis Legg-Calve-Perthes disease

Question 92

How does the presence of FVL influence the management of VTE?

Answer 92

It doesn't influence initial treatment of VTE Doesn't influence the decision of VKA or DOAC May influence duration of anticoagulation although this is individualised; similar to general population, would be more likely to advise indefinite anticoagulation if VTE unprovoked, life-threatening, at unusual site or multiple episodes

Question 93

Do FVL carriers (heterozygotes without personal or family hx of VTE) require any special treatment?

Answer 93

- VTEpr as per general population - Avoid estrogen-containing contraceptives - more likely to anticoagulate during pregnancy/post-partum if other risk factors present - suggest leg exercises/ambulation when flying + consider compression stockings + consider low-dose aspirin (but not supported by high quality evidence) - counsel on risk of VTE/signs etc

Question 94

Is it worth covering individuals with FVL with low dose LMWH during pregnancy to prevent miscarriage or miscarriage?

Answer 94

No - 2023 ALIFE2 trial suggested nil benefit

Question 95

What are other acquired causes of activated Protein C resistance?

Answer 95

Cancer Proteinuria Obesity Smoking Antiphospholipid antibodies Pregnancy Oestrogen / Menopausal hormone therapy Increased factor VIII Note also rare variants in Factor V other than FVL that produce the aPC resistance phenotype eg Factor V Cambridge etc