1. In the context of clotting disorder diagnosis, how do you differentiate between acquired and congenital bleeding disorders, and what tests are commonly employed for this differentiation?
A detailed clinical history will guide whether the clotting disorder is acquired or congenital.
The screening tests performed are Complete Blood Count with Platelet Count, Peripheral Blood Smear Examination, Prothrombin Time, Activated Partial Thromboplastin Time, Bleeding time (by template method), PFA-100, Thrombin Time.
The specialized investigations are ordered after reviewing the screening tests and may include, mixing studies in the case of abnormal PT or APTT, coagulation factor assays to confirm and assess the severity of the coagulation factor deficiency such as in Hemophilia A or B, platelet aggregation studies to confirm platelet qualitative defects and investigations for Von Willebrand disease.
If all baseline screening tests are normal, then investigations for factor XIII deficiency and alpha 2-antiplasmin deficiency are warranted.
It is worth noting that some patients with a definite history of bleeding have normal results for baseline screening tests. Further diagnostic evaluation for such patients is needed to consider mild hemophilia and Von Willebrand disease (VWD), for mild hemophiliacs may have a normal APTT. Therefore, repeated testing may often be needed to diagnose VWD, especially in mild cases because of the fluctuation of Von Willebrand factor in the plasma.
If all investigations are found normal, the patient should be investigated for blood vessel wall abnormalities – hereditary hemorrhagic telangiectasia and Ehlers-Danlos Syndrome, or
acquired like Henoch-Schonlein purpura, scurvy and Cushing’s syndrome.
2. Can you discuss the role of specialized coagulation studies such as mixing studies, factor assays, and platelet function assays (PFAs) in diagnosing clotting disorders?
Mixing studies are typically used to investigate abnormal clotting time results. It helps to distinguish clotting time prolongation due to a coagulation factor deficiency or an inhibitor (specific or nonspecific). Mixing study may direct further coagulation testing but it is not by itself diagnostic.
A coagulation factor test is used to detect problems of the clotting mechanism – too little or too much. Factor assays are performed based upon the PT or APTT test results, which are specific for factors II, V, VII and X or factors VIII, IX, XI and XII, respectively.
The PFA test is a new laboratory screening test of platelet function that measures both platelet adhesion and aggregation (primary hemostasis). Platelet aggregation testing is the gold standard in platelet function testing and can diagnose a variety of inherited and acquired platelet function disorders. It is typically performed at academic medical centers or large hospitals due to the complexity of the testing and interpretation.
3. Could you explain the significance of D-dimer testing in the context of clotting disorders?
D-dimer is a protein fragment from the breakdown of a blood clot. It is normally undetectable or only detectable at a very low level unless the body is forming and breaking down significant blood clots.
The D–dimer test is used to determine the presence of a blood clotting condition e.g., Deep Vein Thrombosis, Pulmonary Embolism, Disseminated Intravascular Coagulation, Stroke. The test cannot reveal what type of clotting condition is present or where the clot is in the body.
4. What are the primary challenges or limitations in diagnosing rare or less common clotting disorders, eg. Haemophilia, thrombophilia, Factor X deficiency? How do you overcome them?
Rare bleeding disorders (RBDs) are inherited deficiencies of coagulation factors such as fibrinogen, Factor (F) FII, FV, FVII, combined FV/FVIII, FX, FXI, and FXIII. They have a low prevalence in the general population.
Inherited hypercoagulable conditions:
Factor V Leiden (most common)
Prothrombin gene mutation (G20210A)
Deficiencies of natural proteins that prevent clotting (antithrombin III, protein C and S)
Dysfibrinogenaemia or hyperfibrinogenaemia
Elevated levels of Factor VIII, IX, XI
Abnormal fibrinolytic system
Acquired hypercoagulable conditions:
Antiphospholipid Syndrome
Disseminated Intravascular Coagulation
The above conditions are precipitated by Cancer, medications, hormone replacement therapy, surgery, heparin-induced thrombocytopenia
The importance of detailed clinical history, screening tests and testing for the above conditions can help arrive at diagnosis. The tests are performed at a few academic centres and molecular pathology labs, where qualified staff with good interpretative skills are present.
