Laboratory Tests
If a doctor suspects that a person's signs and symptoms are due to a bleeding disorder, she may order several laboratory tests. The investigation of a bleeding disorder is usually a step-by-step process. A doctor may begin by ordering screening tests such as Prothrombin Time (PT) and Partial Thromboplastin Time (PTT), which evaluate various components of the clotting process (hemostasis), and a CBC to evaluate the number of platelets present and to determine if bleeding has led to anemia. If the PT and/or the PTT are prolonged, for example, further testing may be done to identify problems with coagulation factors and to see whether or not there may be factor specific inhibitor.
The following table summarizes some of the tests that may be done in the investigation of a bleeding disorder. Not all of the tests listed in the table are needed for each person with a suspected bleeding disorder. The tests are listed in alphabetical order; for detailed information about each test, click on the name of the test to go to the specific article.
Tests for Bleeding Disorders
| Test | Description | Reason for testing | possible significance of Abnormal Results |
|---|---|---|---|
| Blood Smear | Microscopic examination of blood; estimates the number and evaluates appearance and size of platelets | If platelet count is abnormal | Abnormal platelets may indicate a platelet disorder |
| CBC (Complete Blood Count) | Counts the different types of blood cells, including platelets, red blood cells (RBCs), and white blood cells (WBCs), types of WBCs; measures hemoglobin and hematocrit | Routine screen and general test to check for any abnormalities; detects anemia | Decreased platelets may indicate a platelet disorder; anemia may indicate excessive bleeding |
| Coagulation Factors, Activity | Individual tests to measure the activity (function) of specific coagulation factors | If PT or PTT results are abnormal | Decreased activity of one or more factors may indicate factor deficiency or specific factor inhibitor |
| Coagulation Factors, Antigen | Measures the amount of individual factors | When the activity of a specific factor is consistently low | Low level may indicate factor deficiency due to decreased production or increased consumption of a factor |
| D-dimer | Measures a specific type of cross-linked fibrin degradation product | 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 thrombosis, thromboembolism or disseminated intravascular coagulation (DIC) |
| Factor Inhibitors | Detects antibodies directed against individual coagulation factors | If coagulation factor activity test is abnormal | If present, may cause specific factor deficiencies and excessive bleeding |
| Fibrinogen (activity) | 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) | A general screen that evaluates factors XII, XI, IX, VIII, X, V, II (prothrombin), and I (fibrinogen) as well as prekallikrein (PK) and high molecular weight kininogen (HMWK) | Investigate bleeding |
Prolonged PTT suggests need for further tests; may indicate coagulation factor deficiency, specific inhibitor (such as Factor VIII antibody), nonspecific inhibitor (such as Lupus anticoagulant) |
| Platelet Function Tests (aggregation study) | Evaluate platelets' ability to adhere and form clumps (aggregate) | Evaluate bleeding, especially when platelet count is normal | If abnormal, may indicate presence of one of several disorders including von Willebrand's disease |
| Prothrombin Time (PT) | A general screen that evaluates factors VII, X, V, II, and I (fibrinogen) | Investigate bleeding or thrombotic episode | Prolonged PT may suggest need for further tests; may indicate coagulation factor deficiency or dysfunction, or specific factor inhibitor |
| Ristocetin Cofactor | Indirect measure of von Willebrand factor (vWF) activity/function | Evaluate bleeding episodes | If decreased, may indicate low vWF activity and decreased ability for platelets to adhere to injuries; may be due to von Willebrand disease |
| Thrombin Time (TT) | 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 presence of fibrin degredation products, with very low levels of fibrinogen, and with abnormal fibrinogen (e.g., dysfibrinogenemia) |
| von Willebrand Factor (vWF) Antigen | Measures amount of vWF | When activity (measured as Risocetin Cofactor) is low; evaluate bleeding episodes | If low, may indicate platelet-related acquired condition or von Willebrand disease, increased risk of bleeding |
| Thromboelastography (TEG) | Global assessment of clotting abilities, including the functional status of platelets, coagulation cascade, and fibrinolytic activity | When there is need to assess the potential cause of excessive or prolonged bleeding during and after major surgery (e.g., cardiopulmonary bypass) | Abnormal result(s) could be due to quantitative or qualitative defect in platelets, coagulation factors, and/or fibrinolytic factors. The results are useful in guiding patient's management, particularly blood product transfusion. |
Basic metabolic panels may be ordered to assess the liver and kidney functions. Patients with liver and/or kidney failure have increased risk of bleeding.
