Bleeding Disorders
When performing laboratory tests to evaluate bleeding disorders, the coagulation cascade can be thought of as having two branches: the extrinsic pathway and the intrinsic pathway. Each of these pathways utilizes different coagulation factors, proteins that are carried in an inactive form in the blood. These factors are sequentially activated down one pathway or the other and come together to complete the clotting process in the common pathway.
Using this approach, bleeding disorder testing is a step-by-step investigative procedure. If someone presents with a bleeding episode, a doctor may order a Prothrombin Time (PT), which evaluates the extrinsic and common pathways, Partial Thromboplastin Time (PTT), which evaluates the intrinsic and common pathways, and a CBC to see whether or not the patient is anemic and to evaluate the number of platelets present. If the PT is prolonged, further testing may be done to identify problems with factors involved in the extrinsic or common pathway. If the PTT is prolonged, then the doctor may follow-up with other testing to look for specific factor deficiencies in the intrinsic or common pathway and to see whether or not there may be factor inhibitors.
Some of the tests that may be ordered include:
Tests for Bleeding Disorders
| Test | Measures | Ordered When/To | Abnormal Results May Indicate |
|---|---|---|---|
| CBC (Complete Blood Count) | Counts and evaluates size and shape of platelets, red and white blood cells (WBCs), types of WBCs; measures hemoglobin and hematocrit |
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Decreased platelet numbers increase bleeding tendency |
| Coagulation Factors, Activity | Individual tests to measure the function of specific coagulation factors | Evaluate bleeding episodes | Decreased activity of one or more factors may increase risk of bleeding |
| Coagulation Factors, Antigen | Measures the quantity of individual factors | When factor activity is consistently low | Decreased production or increased use of one or more factors, increased risk of bleeding |
| D-dimer | Measures a specific type of cross-linked fibrin degradation | Evaluate blood clot formation during bleeding and clotting episodes | If elevated, indicates recent clotting activity may be due to acute or chronic condition, such as a thromboembolism or disseminated intravascular coagulation (DIC) |
| Factor Inhibitors | Individual tests for coagulation factor antibodies | Evaluate excessive bleeding and prolonged PTT | If present, may cause specific factor deficiencies and excessive bleeding |
| Fibrin degradation Products (FDP) | Reflection of clotting activity and breakdown | Evaluate bleeding and clotting | If increased, indicates recent blood clot formation and breakdown |
| Fibrinogen | Reflection of clotting ability and activity | Evaluate bleeding and clotting | If low, may indicate decreased production or increased use; may be elevated with infection and inflammation. It is an acute phase reactant. |
| Partial Thromboplastin Time (PTT) | Time to clot; evaluates the intrinsic and common pathways of coagulation cascade |
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Prolonged PTT suggests need for further tests. May indicate:
|
| Platelet aggregation (Platelet function test) | Evaluate platelet’s ability to adhere and form clumps | Evaluate bleeding, especially when platelet count normal | If abnormal, increases risk of excessive bleeding; may indicate presence of one of several disorders including von Willebrand’s disease |
| Platelet Function Analyzer | An automated method to measure platelet function (this is the most widely used; there are also other analyzers) | Sometimes used as a presurgical screen or to evaluate recurrent bleeding | Abnormal result may indicate acquired platelet disorder or von Willebrand’s disease. Indicates greater risk of excessive bleeding. This test has largely replaced the Bleeding time test. |
| Prothrombin Time (PT) | Time to clot tes; evaluates the extrinsic and common pathways of coagulation cascade |
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Most common use is monitoring warfarin anticoagulant therapy.
Prolonged PT may suggest need for further tests. May be elevated in inherited or acquired conditions.
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| Ristocetin Cofactor | Indirect measure of von Willebrand factor (vWF) activity/function | Evaluate bleeding episodes | vWF activity and decreased ability for platelets to adhere to injuries; may be due to von Willebrand’s disease, increased risk of bleeding |
| Thrombin Time (TT) | Time to clot; thrombin activates fibrinogen to fibrin stands; TT detects presence of inhibitors to this process | Help evaluate bleeding episode; sometimes when PTT prolonged; when heparin contamination suspected | If elevated, heparin may be contaminating blood sample; also elevated with FDP, with very low levels of fibrinogen, and with abnormal fibrinogen |
| von Willebrand Factor (vWF) Antigen | Quantitative measure of vWF |
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If low, may indicate platelet-related acquired condition or von Willebrand disease, increased risk of bleeding |
