Written By: Dr Anitha Anchan | Published : April 6, 2016 6:52 PM IST
When a blood vessel is damaged, your body naturally responds to stop bleeding and loss of blood. Hemostasis or stoppage of bleeding occurs in three steps blood vessel constriction, platelet plug formation and blood clotting (coagulation). The blood vessel constricts to allow less blood to be lost. Platelets aggregate to form a plug at the injured site to temporarily seal the break in the vessel. The clotting factors are released that activate a complex series of events to form a clot. The clot reinforces the platelet plug. Certain factors are activated once a clot is formed. They slow the clotting process and ultimately begin to dissolve the clot when they are no longer needed.
Insufficient, absent or abnormally functioning platelets or clotting factors hinder the formation of a stable clot. Problems with coagulation can result in bleeding (hemorrhage) or obstructive clotting (thrombosis). An imbalance between clot formation and dissolution can also cause bleeding disorders. The lower or impaired clotting factors cause the impaired blood clotting in hemophilia.
Coagulation test what is it?
Clotting time is the time from the onset of bleeding till the clot formation. Typically, the time varies from 2 to 6 minutes. Clotting time is prolonged in coagulation disorders like hemophilia and conditions like vitamin K deficiency, anticoagulant therapy, disseminated intravascular coagulation, etc. Hemophilia A is caused due to factor VIII deficiency; hemophilia B is due to factor IX deficiency, and hemophilia C is due to factor XI deficiency. In thrombophilia, there is an increased tendency to clot mostly due to an abnormality of a blood-clotting factor which leads to an increase in their function.
Coagulation test or the blood clotting test measures the time required for your blood to clot to assess whether the blood clots normally. During the test, different chemicals are added to your blood sample to identify deficiency or absence of specific clotting factor or factors.
When are the tests recommended?
The coagulation tests are recommended when clotting disorders are suspected and need to be identified. The tests are also used to identify decreased or missing clotting factors and to monitor people who take warfarin or other anticoagulant medicines. The test may be advised prior to surgical procedures and in certain liver diseases.
Reading your coagulation test reports
Some of the general blood tests that are done to assess bleeding and clotting are platelet count, bleeding time, prothrombin time (PT) and activated partial thromboplastin time (aPTT). Various tests are done to measure the amount of specific clotting factor in the blood. These tests include thrombin time, factor V assay, fibrinogen level, D-dimer testing, etc. Your doctor may prescribe one or many of these tests.
1. Platelet Count
Most doctors will prescribe a complete blood count (CBC) as part of your routine examination. While a complete blood count is not a conclusive test, it can give information about the blood cells. Platelets play a significant role in hemostasis by forming a temporary seal. The platelet count parameter measures the number of platelets (the blood cells that help the blood to clot).
Platelet count: Adults: 140,000-400,000 cells/cubic mm
Children: 150,000-450,000 cells/cubic mm
Inference: Increased in bleeding, iron deficiency, cancer or diseases of bone marrow and decreased in idiopathic thrombocytopenic purpura (ITP), celiac disease, leukemia, chemotherapy, etc.
2. Bleeding Time
The time it takes for a platelet plug to form from the onset of bleeding is called bleeding time. Bleeding time test tells the time taken by the small blood vessels in the skin to close to stop the bleeding.
Bleeding time: Normal:1 to 9 minutes in adults:
1-13 minutes in children
9-15 minutes indicates platelet dysfunction
> 15 minutes is critical
Inference: Prolonged in blood vessel defect, defect in platelet aggregation, disseminated intravascular coagulation (DIC) and thrombocytopenia (low platelet count). Drugs like nonsteroidal anti-inflammatory drugs (NSAIDs) and salicylates can also increase bleeding time.
3. Prothrombin Time and INR
Prothrombin time test measures the clotting factors I, II, V, VII, and X. It is used to detect blood clotting disorders, to monitor the anticoagulant warfarin therapy and to determine liver damage and vitamin K status. Increased PT indicates an increased bleeding risk. Decreased PT indicates an increased risk of developing a clot. The international normalized ratio (INR) is a calculation that standardizes prothrombin time. It is used to measure the effect of warfarin therapy.
PT value: 11-134 seconds
INR value: Normal range is 0.8 1.2
During warfarin therapy: 2.0 3.0
Inference: Prolonged in vitamin K deficiency, liver disease, warfarin therapy, disseminated intravascular coagulation (DIC), etc. and decreased in Vitamin K supplementation. Target INR of 2.0-3.0 is considered as ideal during warfarin therapy
4. Activated partial thromboplastin time (aPTT)
Partial thromboplastin time (PTT) is a blood clotting test that helps detect the deficiency in clotting factors I, II, V, VIII, IX, X, XI, & XII. The test does not identify factors VII or XIII deficiencies. In the activated partial thromboplastin time (aPTT) test, an activator is added. This addition speeds up the clotting time. The tests are not only used to detect clotting disorders and to monitor the effects of the anticoagulant heparin therapy but may also at times be used to screen for excessive bleeding risk prior to a surgery.
PTT values: 60-70 seconds is normal
> 100 seconds is critical
aPTT values: 25 to 40 seconds is normal
> 70 seconds is critical
Inference: Prolonged times may indicate coagulation factor deficiency, hemophilia, disseminated intravascular coagulation (DIC), heparin therapy, presence of coagulation factors inhibitors, liver disease, Vitamin K deficiency, antiphospholipid syndrome (APS), etc. Critical values signify spontaneous bleeding.
5. Thrombin Time
Thrombin (activated form of coagulation factor II) mediates the conversion of clotting factor fibrinogen to fibrin during clot formation. Thrombin time (TT) is a clotting test that measures the time required for this thrombin-mediated conversion. It provides information about the level and function of fibrinogen and helps assess the effectiveness of heparin therapy too.
TT value: 12 to 14 seconds
Inference: Prolonged thrombin time may be seen in conditions with decreased or abnormal fibrinogen, heparin therapy, disseminated intravascular coagulation (DIC), liver disease, nutritional deficiency, etc.
6. Factor V Assay
Clotting factor V is one of the proteins involved in blood clotting. It helps convert prothrombin (factor II) into thrombin. The factor V assay measures the level of factor V.
Normal value: 50 200% of the lab reference value
Inference: Abnormally low level may indicate liver disease, disseminated intravascular coagulation (DIC) and primary fibrinolysis.
7. Fibrinogen Test
Fibrinogen (clotting factor I) level in your blood is measured along with other clotting tests to evaluate the clot formation and dissolution. The test can help diagnose disseminated intravascular coagulation (DIC). Abrupt low levels are often related to excessive use of fibrinogen. Persistently low levels may be due to no or decreased fibrinogen production.
Normal value: 150 to 400 mg/dL
Inference: Persistently low levels may be seen in afibrinogenemia, liver disease and severe malnutrition. Abrupt low levels may be seen with disseminated intravascular coagulation (DIC), infection, inflammatory conditions, some cancers and sometimes, following large volume blood transfusions.
8. D-dimer Test
Blood clot dissolution is a natural process that follows blood clot formation. It helps prevent blood clots from growing. D-dimer is a broken fragment present in the blood after a blood clot dissolute. A D-dimer test is mainly used to exclude thromboembolic conditions. It is used in the diagnosis of deep vein thrombosis (DVT) and disseminated intravascular coagulation (DIC). It also aids in monitoring the effectiveness of DIC treatment.
Test report: A normal test is negative.
Inference: Positive test report may indicate thromboembolic conditions, pregnancy, active malignancy and recent surgery1. Decreasing level of D-dimer means the DIC treatment is working.
References
1. Kabrhel C, Mark Courtney D, Camargo CA Jr, Plewa MC, Nordenholz KE, Moore CL, Richman PB, Smithline HA, Beam DM, Kline JA. Factors associated with positive D-dimer results in patients evaluated for pulmonary embolism. Acad Emerg Med. 2010 Jun;17(6):589-97. doi: 10.1111/j.1553-2712.2010.00765.x. PubMed PMID: 20624138; PubMed Central PMCID: PMC3538031.
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