Coagulation Lab values Flashcards
D-Dimer
Qualitative: negative
Quantitative: <250 mcg/L)
This test assess both thrombin and plasmin activity. D-dimer is a fibrin degradation fragment that is made through lysis of cross-linked (D-dimerized) fibrin. As plasmin acts on the fibrin polymer clot, fibrin degradation products and D-dimer are produced. The D-dimer assay provides a highly specific measurement of the amount of fibrin degradation that occurs. Normal plasma does not have detectable amounts of fragment D-dimer. This provides a simple and confirmatory test for disseminated intravascular coagulation (DIC). Positive results of the D-dimer assay correlate with positive results of fibrin degradation products. The D-dimer assay may be more specific than the FDP assay, it is less sensitive. Therefore combining the FDP and the D-dimer may provide high sensitivity and specificity for recognizing DIC. Levels of D-dimer can also increase when a fibrin clot is lysed by thrombolytic therapy. Thrombotic problems such as DVT, PE, Sickle cell anemia, and thrombosis of malignancy are also associated with high D-dimer levels. Recently, D-dimer has been used as an effective screening test for DVT. it is able to accurately identify patients with DVT who are then sent for venous duplex scanning. If the D-dimer test is negative, its high predictability indicates that the patient does not have DVT, and further duplex scanning may not be necessary. Finally, The D-dimer test can be used to determine the duration of anticoagulation therapy in patients with DVT. Patients with an abnormal D-dimer level one month after the discontinuation of anticoagulant therapy have a significant incidence of recurrent DVT. This incidence can be reduced with reinstitution of anticoagulation therapy.
Fibrinogen
200-400 mg/dL (2.0-4.0 g/dL) Critical values (fourth reaction) in the coagulation system. Fibrinogen is converted to fibrin by the action of thrombin during the coagulation process. Fibrinogen, which is produced by the liver, is also an acute-phase reactant protein. It rises sharply during tissue inflammation or tissue necrosis. High levels of fibrinogen have been associated with an increased risk for CAD, stroke, MI, and peripheral arterial disease. Reduced levels can be seen in patients with liver disease, malnourished states, and consumptive coagulopathies (ex. DIC). Large-volume blood transfusions are also associated with low levels, because banked blood does not contain fibrinogen. Reduced levels of fibrinogen will cause prolonged prothrombin (PT) and partial thromboplastin (PTT) times.
Fibrin degradation products
<10mg/L)
Plasminogen
2.4-4.4 Committee on Thrombolytic Agents (CTA) units/mL
Platelet count (Adult)
150,000-400,000/mm^3 (150-400 x -109/L)
This test is performed on patients who develop petechiae (small hemorrhages in the skin), spontaneous bleeding, increasingly heavy menses, or thrombocytopenia. It is used to monitor the course of the disease or therapy for thrombocytopenia or bone marrow failure. Platelets main role is maintenance of vascular integrity. In blood vessel injury, hemostasis is required to form a clot that will durably plug the hole until healing can occur. The primary phase of the hemostatic mechanism involves platelet aggregation. From there, the platelets help initiate the coagulation factor cascade. Most of the platelets exist in the bloodstream. A smaller percentage ( 25%) exists in the liver and spleen. Survival of platelets is measured in days (average 7 to 9 days). Counts less than 100,000.mm^3 are considered to indicate thrombocytopenia; Thrombocytosis is said to exist when counts are greater than 400,000 mm^3. Thrombocythemia is a term used to indicate a platelet count in excess of 1 million/mm^3. Vascular thrombosis with tissue or organ infarction is the major complication of thrombocythemia. The most common diseases associated with spontaneous thrombocytosis are iron deficiency anemia and malignancy (leukemia, lymphoma, solid tumors such as of the colon). Thrombocytosis may also occur with polycythemia vera and postsplenectomy syndromes. It should be noted that even patients with elevated platelet counts can experience a bleeding tendency because the function (platelet aggregation) of those platelets may be abnormal. It is not uncommon for patients whose platelet counts exceed 1 million to experience spontaneous bleeding and thrombocytosis. Spontaneous bleeding is a serious danger when platelet counts fall below 20,000 mm^3. Petechiae and ecchymosis will also occur at that degree of thrombocytopenia. Causes of thrombocytopenia include: reduced production of platelets (secondary to bone marrow failure or infiltration of fibrosis, tumor, etc.). Accelerated destruction of platelets (secondary to antibodies, infections, drugs, prosthetic heart valves). Consumption of platelets (secondary to disseminated intravascular coagulation). Platelet loss form hemorrhage. Dilution with large volumes of blood transfusions containing very few, if any, platelets.
Platelet antibodies
None
To assess for the presence of platelet antibodies to assist in diagnosing thrombocytopenia related to autoimmune conditions and platelet transfusion compatibility issues.
Prothrombin time (PT)
11-12.5 sec Full anticoagulant therapy > 1.5-2 times control value 20%-30% INR: 0.8-1.1
Critical values: PT >20 seconds, INR: 5.5
This is used to evaluate the adequacy of the extrinsic system and common pathway in the clotting mechanism.
A prothrombin time test can be used to check for bleeding problems. PT is also used to check whether medicine to prevent blood clots is working. Blood clotting factors are needed for blood to clot (coagulation). Prothrombin, or factor II, is one of the clotting factors made by the liver. Vitamin K is needed to make prothrombin and other clotting factors. Prothrombin time is an important test because it checks to see if five different blood clotting factors (factors I, II, V, VII, and X) are present. The prothrombin time is made longer by:
Blood-thinning medicine, such as heparin. Another test, the activated partial thromboplastin time (APTT) test, is a better test to find out if the right dose of heparin is being used.
Low levels of blood clotting factors.
A change in the activity of any of the clotting factors.
The absence of any of the clotting factors.
Other substances, called inhibitors, that affect the clotting factors.
An increase in the use of the clotting factors.
An abnormal prothrombin time is often caused by liver disease or injury or by treatment with blood thinners.
Another blood clotting test, called partial thromboplastin time (PTT), measures other clotting factors. Partial thromboplastin time and prothrombin time are often done at the same time to check for bleeding problems or the chance for too much bleeding in surgery.
Why It Is Done
Prothrombin time (PT) is measured to:
Find a cause for abnormal bleeding or bruising.
Check to see if blood-thinning medicine, such as warfarin (Coumadin), is working. If the test is done for this purpose, a PT may be done every day at first. When the correct dose of medicine is found, you will not need so many tests.
Check for low levels of blood clotting factors. The lack of some clotting factors can cause bleeding disorders such as hemophilia, which is passed in families (inherited).
Check for a low level of vitamin K. Vitamin K is needed to make prothrombin and other clotting factors.
Check how well the liver is working. Prothrombin levels are checked along with other liver tests, such as aspartate aminotransferase and alanine aminotransferase.
Check to see if the body is using up its clotting factors so quickly that the blood can’t clot and bleeding does not stop. This may mean the person has disseminated intravascular coagulation (DIC).
Partial Thromboplastin Time (PTT)
60-70 sec
critical values: aPTT: >70 sec, PTT: >100 sec
The PTT test is used to asses the intrinsic system and the common pathway of clot formation. It is also used to monitor heparin therapy. longer-than-normal PTT or APTT can mean a lack of or low level of one of the blood clotting factors or another substance needed to clot blood. This can be caused by bleeding disorders, such as hemophilia or von Willebrand’s disease.
A longer-than-normal PTT or APTT can be caused by liver disease, kidney disease (such as nephrotic syndrome), or treatment with blood thinners, such as heparin or warfarin (Coumadin).
A longer-than-normal PTT may be caused by conditions such as antiphospholipid antibody syndrome or lupus anticoagulant syndrome. These conditions happen when the immune system makes antibodies that attack blood clotting factors. This can cause the blood to clot easily in veins and arteries.
The PTT can get longer when you are using heparin, so your PTT value needs to be closely checked. If you have a longer PTT, you may have a higher risk of bleeding.`
Activated Partial Thromboplastin TIme (APTT)
30-40 sec
Recently activators have been added to the PTT test reagents to shorten normal clotting time and provide a narrow normal range. This shortened time is called the activated PTT. Desired ranges for therapeutic anticoagulation are 1.5 to 2.5 times normal (ex. 70 sec).
