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Laboratory tests

Bleeding disorder testing is a step-by-step investigative procedure. You usually cannot tell the cause of the bleeding by its location, timing or severity. To evaluate a bleeding tendency useful tests are a PT (prothrombin time – evaluates the extrinsic and common pathways), APTT (activated partial thromboplastin time – evaluates the intrinsic and common pathways), full blood count (FBC) first to see whether or not the patient is anaemic, and to measure the platelet count.  If the APTT is prolonged, then follow-up is done with other testing to look for specific factor deficiencies and to see whether or not there may be factor inhibitors.

Some of the tests that may be ordered include:

Tests for bleeding disorders

The tests listed here are the more common tests performed to evaluate bleeding disorders.
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
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
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
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 pre-surgical 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 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
Pre-surgical 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
von Willebrand Activity (vWF:GP1bM assay) Direct measure of von Willebrand factor (vWF) activity/function Evaluate bleeding episodes The older RiCoF assay used Ristocetin to bridge Glycoprotein1b and vWF. This replacement assay uses modified Gp1b removing the need for ristocetin and is more easily standardised.
 
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 protein Done when activity  is low. Evaluate bleeding episodes If low, may indicate platelet related acquired condition or von Willebrand disease, increased risk of bleeding
 

Last Review Date: May 1, 2018