Acquired hemophiliaPocket card

Issue number 3 2012

Incidence Underlying defect

Inheritance Severity

Hemophilia A 1/4,000–5,000 male births~80% hemophilia cases

FVIII deficiency X-linked recessive*

Severity varies largely depending on factor level

Hemophilia B (Christmas disease)

1/25,000 male births~15–20% hemophilia cases

FIX deficiency X-linked recessive*

Severity varies largely depending on factor level

Hemophilia C Rare (1/100,000) overall but common in Jews of Ashkenazi descent

FXI deficiency Autosomal recessive but not complete; heterozygous individuals also show increased bleeding

Generally mild; degree of severity unrelated to factor level; at risk of bleeding following surgery or major trauma

Acquired hemophilia

1–2/1,000,000 worldwide

Autoantibodies to FVIII or rarely FIX; can be idiopathic or associated with a wide range of illnesses/conditions

No known genetic link

Ranges from severe and life-threatening to mild

Main types of hemophilia:Summary

* 10% of female carriers are symptomatic, typically with mild disease

Table 1

Table 2

Classification of hemophiliaseverity

Severity Factor activity IU/mL Bleeding tendency

Mild 5–40% 0.05–0.40 Few or no bleeding episodes; bleeding may occur with major trauma or surgery; no spontaneous bleeding

Moderate 1–5% 0.01–0.05 Bleeding may occur with minimal trauma or minor surgery; spontaneous bleeding rare (variable)

Severe <1% <0.01 High risk of severe, spontaneous bleeding

Effect of hemophilia on normal hemostasis

INTRINSICUnphysiological surfaces

Hemophilia B

Hemophilia A

Plateletaggregation Tissue factor (TF)

Prothrombin

Fibrinogen

FibrinopeptidesA B

Plasminogen activator

Plasminogen Plasmin

Fibrin FibrinFibrin

degradationproducts

Thrombin

Contact activation(collagen, cell fragments, glass)

EXTRINSICLesion

XII

XI XIa

X XXa

IX

V

VIII VIIIa

IXIXa

VaXIII

XIIIa

XIIa VIIa VII

Hemophilia C

Acquired hemophilia:Antibodies to FVIII or FIX

Fig. 1

Inheritance of hemophilia Aand B

‘Carrier’ father and mother without hemophilia

Father (without hemophilia)

Father (withhemophilia)

Mother (not a carrier)

Normalmale

Normalfemale

Carrierfemale

Normalmale

Carrierfemale

Normalmale

Carrierfemale

Male with hemophilia

Mother (carrier for hemophilia gene)

+

X Y

X Y XX

X XH

X XH XH Y X Y X XHX XH XY

Father with hemophilia and mother who is not a carrier

XH Y X X

Fig. 2

Hemophilia A and B: Laboratory work-up

•Standardhemostasis - Normal PT, bleeding time, platelet

count, fibrinogen - aPTT prolonged (severe and moderate

disease); corrected on mixing tests - a normal aPTT may not exclude mild

hemophilia because of the relative insensitivity of the test

•ReducedFVIII–hemophiliaA - Mild hemophilia A is not excluded by

the finding of a normal FVIII level by one-stage chromogenic assay; should be checked using a two-stage clotting or chromogenic assay in patients with a clinical history compatible with hemophilia A

- Conditions that can increase FVIII levels (e.g. ABO blood type, stress, exercise) can obscure the diagnosis of hemophilia A

•ReducedFIX–hemophiliaB - Measurement in neonates may need to

be repeated where family history of mild disease exists

• Differentialdiagnosis -vonWillebranddisease(vWD)should

be ruled out in patients with decreased FVIII levels

- Bleeding time (BT) may be prolonged invWD

- Test von Willebrand factor antigen and ristocetin cofactor activity

Inhibitor development during replacement therapy

•Approximately30%ofindividualswithsevere hemophilia A treated with FVIII replacement therapy develop inhibitory antibodies (‘inhibitors’) to FVIII

•LesscommoninhemophiliaB(2–3%)

•Highestriskinpatientswithseveredisease

•Developmentofinhibitorsassociatedwithdiminished treatment effect or treatment failure, and/or uncontrolled bleeding

• InpatientswithhemophiliaB,development of inhibitors may be associated with infusion and anaphylactoid reactions to continued FIX therapy

•Classification: -Lowresponders:inhibitorlevels

<5 Bethesda units (BU) -Highresponders:inhibitorlevels>5BU

FVIII and FIX inhibitor testing

•Frequencyoftestingforinhibitorsinhemophilia A and B should reflect the type and severity of hemophilia, the regimen of factor replacement (prophylactic or on-demand) and the extent of prior exposure to factor concentrate:

- Initial screening -Every5exposuredays(EDs)until20

EDs -After21EDs,every10EDsuntil50

EDs -Atleasttwiceayearuntil150EDs

- Follow-up screening - Annually thereafter - Whenever clinically indicated - Before and after surgery - Before and after a switch of replacement

products - If positive, repeat and check recovery of

factor concentrate

•Tests -Screening:aPTTprolonged,not

corrected on mixing studies - Inhibitor assay (Bethesda/Nijmegen)

The Bethesda/Nijmegeninhibitor assay

•BU,Bethesdaunits(definedastheamount of an inhibitor that will neutralise 50%of1unitofFVIII:Cinnormalplasmaafter120minutesincubationat37°C)

•FVIII,FactorVIII

•Differencesbetweenthetwomethodsarecircled.

•FVIIIstabilityinNPPiscompromisedbyfactors such as pH

•ThiscanleadtofalsepositiveBethesdaresults

•TheNijmegenmodificationaddressesthis by using buffered NPP and by substituting FVIII deficient plasma for buffer.

Classical Bethesda Assay

Normalpooledplasma(NPP)

Incubate2h @ 37ºC

Measure FVIII activity in mixtures

Patient FVIII activity/control FVIII activity = corrected residual FVIII activity

Convert residual FVIII activity to BU/mL using a converter table/chart andmultiply BU/mL value by dilution factor for corrected BU/mL titer

Patientplasma

Patient1:1 mixture

Control1:1 mixture

Imidazolebuffer

(pH 7.4)

Nijmegan Modification

BufferedNPP

(pH 7.4)

Incubate2h @ 37ºC

Measure FVIII activity in mixtures

Patientplasma

Patient1:1 mixture

Control1:1 mixture

FVIII-deficientplasma

Fig. 3

Acquired autoantibodies(inhibitors) against Factor VIII in non-hemophiliacs*

•Estimatedincidenceof1–4casespermillion per year

•Noknowngeneticinheritancepattern

•Majorityofcasesareidiopathic,butmay be associated with a range of autoimmune diseases (e.g. systemic lupus erythematosus, rheumatoid arthritis), drugs (e.g. penicillin, interferon), infections or during pregnancy

•Classicallypresentswithbleedingranging from acute, life-threatening haemorrhage (9–22% mortality) to mild bleeding that requires no treatment in patients with no personal or family history of bleeding

•Principalmanifestationsarebleedinginto the skin (purpura) and soft tissues; bleeding into the joints (hemarthroses) is less common compared with inherited hemophilia

•Bleedscanbeserious,leadingtoseveremorbidity and possible mortality if untreated

•Clinicalphenotypedoesnotcorrelatewith Factor VIII level or inhibitor titre

• Initialhemostasistestingshowsisolated prolonged activated partial thromboplastin time (aPTT), with normal prothrombin time (PT), bleeding time and platelet count, and reduced FVIII

* Inhibitor antibodies to Factor VIII or Factor IX may arise as alloantibodies in patients withhemophiliaA(upto20–30%)orB(upto3–5%)treatedwithexogenousFactorVIIIor Factor IX, respectively

Algorithm for the managementof patients with suspected acquired hemophilia

From:Collinsetal.Consensusrecommendationsforthediagnosisandtreatment ofacquiredhemophiliaA.BMCResNotes2010;3:161.© BioMed Central Open Access license agreement.

Isolated prolonged aPTT

Mixing test

aPTT correction Weak/no aPTT correction

Suspect acquired hemophilia or LA

Tests for LAMeasure FVIII and inhibitor

PositiveNegativeAcquired hemophilia

Lupus Anticoagulant

Consult comprehensivecare hemophilia center

Suspect clotting factor deficiency

Measure FVIII, IX, XI, XII

Single factor deficiency

Confirm aPTT

Exclude heparin contamination

Consider anticoagulant influence

Acute bleeding

Occult bleeding

No bleeding

37C at 0 and 2 hrs

Time and temperaturedependent

Not time and temperaturedependent

Suspect coagulationfactor deficiency or LA

Negative personal andfamily history of

bleeding disorder

Fig. 4

Laboratory diagnosis ofhemophilia: Summary

* May be normal in mild forms

** Mild hemophilia A is not excluded by the finding of a normal FVIII level by one-stage chromogenic assay; should be checked using a two-stage clotting or chromogenic assay in patients with a clinical history compatible with hemophilia A

Standard hemostasis tests

PT aPTT BT Platelet levels Fibrinogen

Hemophilia A

Hemophilia B

Acquired hemophilia

Differentialdiagnoses

von Willebrand disease

Disseminatedintravascular coagulation

Specific assays

Factor VIII Factor IX Mixing test Other

Hemophilia A aPTT corrected

Genetic testing F8

Hemophilia B aPTT corrected

Genetic testing F9

Acquired hemophilia

Weak/no aPTT correction

Rule out lupus anticoagulant (Russell viper venom test) FVIII inhibitor assay

Differentialdiagnoses

von Willebrand disease

aPTT corrected

von Willebrand factorantigen; ristocetin cofactor activity

Disseminatedintravascular coagulation

aPTT corrected

Soluble fibrin monomer (SF)D-dimer,fibrindegradation productsAntithrombin and Protein C

Table 3

Table 4

ReferencePeerschke et al. (2009). Am J Clin Pathol;131: 552–58.

©2009 American Society for Clinical Pathology ©2009 American Journal of Clinical Pathology

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