Functional Platelet Disorders

Diagnosis

Indications for Testing

  • Lifelong history of
    • Easy bruisability
    • Frequent ecchymoses
  • Family history of bleeding disorders
  • Unexplained thrombocytopenia in infants and children

Laboratory Testing

  • Rule out more common causes of platelet-type bleeding (eg, VWD, acquired platelet dysfunction)
  • Initial testing – CBC with platelet count and peripheral smear to evaluate platelet morphology and size indices; basic coagulation tests (PT, PTT, fibrinogen)
    • Bleeding test not recommended – invasive, highly dependent on operator, lacks sensitivity and specificity
  • Further testing using platelet aggregation studies when functional disorders are suspected
    • Platelet aggregation studies must be performed locally due to requirement for fresh patient platelets and limited sample stability (~4 hours stability)
    • Prior to testing, the patient should have discontinued any medications that affect platelet function (eg, aspirin, NSAIDs) to assure that any abnormalities observed are due to an underlying intrinsic qualitative platelet disorder and not medication effect

Inherited Platelet Disorders – Diagnosis

Disorder

Diagnosis

Bernard-Soulier syndrome

Platelet count – decreased; giant platelets

Peripheral smear – giant platelets (similar in size to red blood cells)

Aggregation studies – failure to aggregate with high-dose ristocetin; normal aggregation with other agonists (note: patients with severe von Willebrand disease may have a similar aggregation profile)

Platelet flow cytometry – decreased expression of GPIb/IX/V (CD42b); flow cytometry may be normal with qualitative defects of CD42b

von Willebrand disease (VWD)

Platelet count and morphology – normal in most subtypes

Aggregation studies – may be normal, have reduced aggregation with high-dose ristocetin, or have abnormally increased aggregation with low-dose ristocetin, depending on subtype. Platelet aggregation is not considered first-line testing for VWD

VWD due to quantitative or qualitative defects in von Willebrand factor (VWF) rather than a platelet defect

Initial testing for VWD includes VWD antigen, VWF activity (ristocetin cofactor activity), and factor VIII activity

Multimeric analysis used for subtyping after initial diagnosis; ristocetin-induced platelet aggregation useful in certain cases but is not sensitive to mild forms of VWD

Pseudo-VWD (platelet-type) has similar clinical and laboratory features to type 2B VWD; they are differentiated by VWF:PB (platelet binding) assay (also called type 2B binding) or molecular studies

Glanzmann thrombasthenia

Platelet count and platelet morphology – normal

Aggregation studies – no response to epinephrine, adenosine 5'-diphosphate (ADP), collagen, arachidonic acid, or thrombin; normal aggregation to ristocetin (Note: Patients with afibrinogenemia will have a similar aggregation profile)

Platelet flow cytometry – decreased expression of GPIIb/IIIa (CD41/CD61); flow cytometry may be normal with qualitative defects of GPIIb/IIIa

Abnormal clot retraction (testing not widely available)

Oculocutaneous albinism (Hermansky-Pudlak syndrome)

Platelet count and morphology – normal

Electron microscopy – decreased or absent dense granules

Aggregation studies – see delta storage pool deficiency below

Chediak-Higashi syndrome

Platelet count and morphology – normal

Peripheral blood/marrow smears – abnormal granules in blood and marrow leukocytes

Electron microscopy – decreased or absent dense granules

Aggregation studies – see delta storage pool deficiency below

Wiskott-Aldrich syndromePlatelet count and morphology – decreased number and abnormal platelets (small)

Gray-platelet syndrome (alpha granule deficiency)

Platelet count and morphology – decreased number and abnormal morphology (agranular)

Peripheral smear – large gray (agranular) platelets; must be distinguished from acquired agranular platelets due to ongoing platelet activation

Aggregation studies – variable aggregation abnormalities; tend to have abnormal platelet secretion induced by ADP/collagen, modified thrombin responses

Electron microscopy – decreased alpha granules

Delta storage pool deficiency (dense granule deficiency)

Platelet count and morphology – normal

Aggregation studies – absent secondary wave in response to ADP and epinephrine; possible decreased aggregation to collagen and ristocetin; can stimulate secondary wave response to ADP by using high concentrations of ADP; aggregation studies may be normal in some patients

Electron microscopy – decreased or absent dense granules

Differential Diagnosis

  • Thrombocytopenia
    • Inherited thrombocytopenias
    • Decreased platelet production due to bone marrow disorders – leukemias (eg, ALL, AML, MDS)
    • Increased platelet destruction
      • Immune causes
      • Non-immune causes (mechanical destruction)
      • Platelet sequestration in spleen
  • Antiplatelet medications – non-steroidal anti-inflammatory drugs (NSAIDs), acetyl salicylic acid (ASA), Plavix
  • Myeloproliferative neoplasms or lymphoproliferative disorders
  • Macrothrombocytopenias with neutrophilic inclusions (MYH9 disorders)
    • May-Hegglin anomaly, Sebastian syndrome, Fechtner syndrome, Epstein syndrome
  • Thrombocytopenia with small platelets (X-linked thrombocytopenia)
  • Oculocutaneous albinism
    • Griscelli syndrome
    • Waardenburg syndrome II

Clinical Background

Platelet dysfunction is frequently associated with excessive bleeding (frequently mucosal) and can be acquired or inherited.

Epidemiology

  • All inherited disorders are rare
  • Age – onset depends on disorder

Risk Factors

  • Acquired conditions
  • Genetics – family history of inherited disorders

Pathophysiology

  • Platelets originate from bone marrow megakaryocytes and have a life span of 5-10 days
  • Normal platelet function
    • Maintain vascular integrity and prevent prolonged bleeding
    • Circulate in close contact with endothelial cells
    • Adhere to blood vessel wall after vascular injury
      • Adhesion activates platelets, causing recruitment of additional platelets to site
      • Recruited platelets aggregate to form temporary platelet plug (the initial seal that stops bleeding)
  • Abnormalities in platelet function involve adhesion defects, release defects (granule deficiency or signal transduction defects) and aggregation abnormalities

Clinical Presentation

  • Inherited platelet disorders – autosomal recessive

    Inherited Platelet Disorders – Autosomal Recessive

    Disorder/Inheritance

    Defect/Gene(s)

    Clinical Presentation

    Bernard-Soulier syndrome

    Autosomal recessive

    Deficiency or dysfunction of platelet GPIb-IX-V complex (adhesion disorder)

    GP1BA, GP1BB, GP9

    Epistaxis, ecchymoses, menorrhagia, gingival hemorrhage, gastrointestinal bleeding

    Thrombocytopenia absent radius syndrome

    Autosomal recessive

    Elevated thrombopoietin

    Low megakaryocytes

    Defect is in megakaryocytic differentiation and platelet production

    Unknown mutation

    Cardiovascular defects (eg, tetralogy of Fallot), absent radii

    Glanzmann thrombasthenia

    Autosomal recessive

    Deficiency of dysfunction of platelet glycoprotein IIb-IIIa (aggregation disorder)

    ITGA2B, ITGB3

    Menorrhagia, ecchymoses, epistaxis, gingival hemorrhage

    Hermansky-Pudlak syndrome (plus oculocutaneous albinism)

    Autosomal recessive

    Scarce or absent granules (storage pool disorder)

    HPS1, AP3B1, HPS3-6, DTNBP1, BLOC1S3, BLOC1S6

    Oculocutaneous albinism, excessive mucosal bleeding, deposition of ceroid lipofuscin in organs, pulmonary fibrosis

    Chediak-Higashi syndrome (plus oculocutaneous albinism, neutropenia, increased infections)

    Autosomal recessive

    Scarce or absent granules (storage pool disorder)

    LYST (previously known as CHS1)

    Oculocutaneous albinism, recurrent infections, loss of pigment in hair and skin, central nervous system ataxia common, excessive mucosal bleeding

    Gray-platelet syndrome (alpha storage pool disease)

    Autosomal recessive or autosomal dominant

    Decreased alpha granules (storage pool disorder)

    NBEAL2

    Mild mucosal bleeding, myelofibrosis, splenomegaly

    Delta storage pool deficiency (dense granule deficiency)

    Autosomal dominant; autosomal recessive in association with some syndromes listed above

    Abnormal or decreased dense granules (storage pool disorder)

    May occur alone or as a component of other hereditary disorders (see above)

    Mucosal bleeding

    If part of a hereditary syndrome, features of the syndrome will also be present

    Congenital amegakaryocytic thrombocytopenia

    Autosomal recessive

    Severe thrombocytopenia

    Lack of megakaryocyte precursors

    Elevated thrombopoietin

    MPL

    Progressive bone marrow failure

    No physical anomalies

    Inherited platelet disorders – autosomal dominant

    Inherited Platelet Disorders – Autosomal Dominant

    Disorder/Inheritance

    Defect/Gene(s)

    Clinical Presentation

    Pseudo-von Willebrand disease (VWD) (platelet-type VWD)

    Autosomal dominant

    Gain of function of platelet GPIb-IX-V complex – resembles VWD type 2B (adhesion disorder)

    GP1BA

    Epistaxis, ecchymoses, menorrhagia, gingival hemorrhage

    Gray-platelet syndrome (alpha storage pool disease)

    Autosomal recessive or autosomal dominant

    Decreased alpha granules (storage pool disorder)

    NBEAL2

    Mild mucosal bleeding, myelofibrosis, splenomegaly

    Delta storage pool deficiency (dense granule deficiency)

    Autosomal dominant; autosomal recessive in association with some syndromes listed above

    Abnormal or decreased dense granules (storage pool disorder)

    May occur alone or as a component of other hereditary disorders (see above)

    Mucosal bleeding

    If part of a hereditary syndrome, features of the syndrome will also be present

    May-Hegglin anomaly

    Sebastian syndrome

    Fechtner syndrome

    Epstein syndrome

    Autosomal dominant

    Abnormal nonmuscle myosin (a cytoskeletal protein for platelet formation)

    MYH9

    Nephritis, hearing loss for Fechtner and Epstein syndromes

    Mediterranean macrothrombocytopenia

    Autosomal dominant

    Similar defect to Bernard-Soulier syndrome

    GP1A

    Mild bleeding

    Paris-Trousseau syndrome

    Autosomal dominant

    Transcription factor dysfunction

    FLI1

    Severe thrombocytopenia psychomotor disability, trigonocephaly, facial dysmorphism, cardiac abnormalities

    Familial platelet disorder with predisposition to acute myelogenous leukemia

    Autosomal dominant

    Core binding transcription factor defect

    RUNX1

    Predisposition to AML or MDS

    Inherited platelet disorders – X-linked

    Inherited Platelet Disorders – X-Linked

    Disorder/Inheritance

    Defect/Gene(s)

    Clinical Presentation

    Wiskott-Aldrich syndrome

    X-linked

    Decreased small platelets, few alpha granules, lack delta granules

    WAS

    Eczema, recurrent infections, severe bleeding

    X-linked macrothrombocytopenia

    X-linked

    Transcription factor defect

    GATA1

    Mild to moderately severe bleeding

  • Acquired disorders include the following

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
CBC with Platelet Count 0040002
Method: Automated Cell Count

Identify thrombocytopenia

   
Prothrombin Time 0030215
Method: Electromagnetic Mechanical Clot Detection

Identify other potential causes for bleeding disorder

   
Partial Thromboplastin Time 0030235
Method: Electromagnetic Mechanical Clot Detection

Identify other potential causes for bleeding disorder

   
Platelet Aggregation Studies 0030160
Method: Qualitative Aggregation

Evaluate patients with suspected inherited qualitative platelet disorders

Evaluate patients with lifelong platelet-type bleeding

This is a time-sensitive test – this test is only available for local clients due to 4-hour sample stability

Do not order this test if platelets are decreased (<100,000/μL)

 
Fibrinogen Panel 0030137
Method: Electromagnetic Mechanical Clot Detection/Radial Immunodiffusion

Identify other etiologies for bleeding

   
von Willebrand Panel 0030125
Method: Electromagnetic Mechanical Clot Detection/Platelet Agglutination/Microlatex Particle-Mediated Immunoassay

Rule out VWD

Panel includes VWD antigen, ristocetin cofactor activity and factor VIII activity