| Test |
Measures |
Ordered when/to |
Abnormal results may indicate |
| aPTT (activated partial thromboplastin time) |
Time to clot test. Evaluates the intrinsic and common pathways of coagulation cascade |
- Investigate bleeding
- Pre-surgical screen for risk of excessive bleeding
- Monitor heparin anticoagulant therapy |
Prolonged aPTT suggests need for further tests.
May indicate:
- Coagulation factor deficiency
- Specific inhibitor (such as Factor VIII antibody)
- Nonspecific inhibitor (such as lupus anticoagulant)
- Patient on heparin and/or blood sample contaminated with heparin |
| FBC (full blood count) |
Counts and evaluates size and shape of platelets, red and white blood cells (WBCs), types of WBCs. Measures haemoglobin and haematocrit |
Ordered as a routine screen, to check for any abnormalities |
Decreased dysfunctional platelets may increase the risk of bleeding |
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 1 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 DIC (disseminated intravascular coagulation) |
| Factor inhibitors |
Individual tests for coagulation factor antibodies |
Evaluate excessive bleeding and prolonged aPTT |
If present, may cause specific factor deficiencies and excessive bleeding |
| Fibrinogen |
Reflection of clotting ability and activity |
Evaluate bleeding and clotting |
If low, may indicate decreased production or increased use. May be elevated with inflammation. It is an acute phase reactant |
| Platelet aggregation |
Evaluate platelet’s ability to form clumps |
Evaluate bleeding, especially when platelet count normal |
If prolonged increases risk of excessive bleeding, may indicate presence of one of several disorders including von Willebrand’s disease |
| Platelet function analyser |
An automated method to measure platelet function (this is the most widely used, there are also other analysers) |
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 |
| PT (prothrombin time) |
Time to clot test. Evaluates the extrinsic and common pathways of coagulation cascade |
Investigate bleeding or thrombotic episode
Presurgical screen for risk of excessive bleeding
Monitor warfarin (coumadin) anticoagulant therapy |
Most common use is monitoring warfarin anticoagulant therapy
Prolonged PT may suggest need for further tests. May be elevated in inherited or acquired conditions |
| 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 aPTT 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 |
Done 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 |
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