Characteristics of Glanzmann Thrombasthenia: Laboratory Findings
Severe thrombocytopenia is NOT a characteristic laboratory finding in patients with Glanzmann thrombasthenia. 1
Laboratory Profile of Glanzmann Thrombasthenia
Glanzmann thrombasthenia (GT) is a rare autosomal recessive bleeding disorder characterized by specific laboratory abnormalities:
Platelet Count: Normal platelet count is typically present in GT patients. The absence of thrombocytopenia is a key distinguishing feature 1, 2
Glycoprotein Expression: Deficient GPIIb/IIIa (integrin αIIbβ3) is the hallmark of GT, detected by flow cytometry showing reduced or absent expression of CD41 (GPIIb) and/or CD61 (GPIIIa) 1, 3
Bleeding Time: Increased bleeding time is consistently observed in GT patients due to impaired platelet aggregation 1, 4
Platelet Aggregation: Abnormal platelet aggregation with multiple agonists including ADP, collagen, and epinephrine is characteristic. This is due to the inability of platelets to bind fibrinogen, which is essential for platelet-platelet interactions 1, 5
Diagnostic Laboratory Testing
The diagnosis of GT is confirmed through:
Light Transmission Aggregometry (LTA): Shows severely reduced or absent aggregation in response to multiple physiological agonists (ADP, collagen, epinephrine) but normal agglutination with ristocetin 1, 3
Flow Cytometry: Demonstrates deficient or absent expression of GPIIb/IIIa complex 1, 5
Peripheral Blood Smear: Shows normal platelet morphology and count 1
Coagulation Studies: PT and aPTT are typically normal 1
Clinical Correlation
GT patients present with:
- Mucocutaneous bleeding (epistaxis, gingival bleeding)
- Easy bruising
- Menorrhagia in women
- Gastrointestinal bleeding
- Prolonged bleeding after trauma or surgery
The severity of bleeding can vary between patients despite similar laboratory findings, suggesting that other factors may influence the clinical phenotype 5.
Common Pitfalls in Diagnosis
- Misdiagnosis: GT may be confused with other platelet function disorders or immune thrombocytopenia
- Incomplete Testing: Relying solely on platelet count without platelet function studies may miss the diagnosis
- Overlooking Normal Platelet Count: The presence of normal platelet count with bleeding symptoms should prompt consideration of platelet function disorders like GT
Remember that while GT patients have defective platelet aggregation, they maintain a normal platelet count, which distinguishes this condition from thrombocytopenic disorders 2, 4.