| Which of the following is not a variable in the effectiveness of hemostasis? | View Page |
| The organ associated with the production of the vast majority of clotting factors is the: | View Page |
| What laboratory test result is commonly used to monitor oral anticoagulant therapy? | View Page |
| An Introduction to the Fundamentals of Coagulation The ability of the body to maintain a state of homeostasis, or physiological equilibrium, is absolutely essential for effective, efficient functionality of all body systems.
The mechanisms involved in blood coagulation, also known as hemostasis or blood clotting, serve to illustrate this concept.
Hemostasis is the cessation of free blood flow, external to the vascular system, when a vessel wall has been breached.
With the maintenance of homeostasis in mind, it is vital that the body be able to rapidly repair vascular damage, arresting blood flow in the process, while simultaneously maintaining blood in a fluid state within the vascular compartment.
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| An Introduction to the Fundamentals of Coagulation Blood flow is arrested by way of a complex series of interrelated physiological and biochemical processes. There are a wide variety of factors that influence the effectiveness of hemostatic processes including the following: Type of, and degree of, vessel damage Ability of vasoconstriction to occur Availability of platelets & their functionality Availability of clotting factors & their functionality Absence of inhibitors & anticoagulants | View Page |
| An Introduction to the Fundamentals of Coagulation Vessel size as related to time required for clotting to occur, amount of products used (platelets and clotting factors), and size of the corresponding bleed. | View Page |
| Primary Hemostasis – Characteristics of the Platelet Platelets play a significant role in primary hemostasis, as they are the “bricks”, or building blocks of the developing platelet plug, the forerunner to the end stage fibrin clot. Platelets have inherent adhesive properties which are essential for adherence to the site of vascular damage, and for binding to one another in aggregation activities. Platelets must be present in sufficient number, and be functionally active for optimal clotting to occur. Platelet functionality tends to be more crucial than the number of platelets available, however, as patients with lower platelet counts can still clot relatively effectively as compared to those patients with intrinsic platelet defects. | View Page |
| Tests of Hemostatic Function – Fibrinogen Assay The fibrinogen assay performed in the clinical laboratory is a quantitative measure of factor I.
This assay is used to determine whether there is enough fibrinogen present to allow for normal clotting.
It is performed in cases of an unexpected, prolonged bleeding event, or an unexpected abnormal PT and/or APTT.
Additionally, it is also used to aid in the diagnosis of disseminated intravascular coagulation (DIC).
A normal reference range is typically around 200-400 mg/dl.
That range is significant because fibrinogen levels
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| Coagulation Disorders - Acquired Disseminated Intravascular Coagulation (DIC) is best described as a disorder of consumption, because clotting factors are depleted from the blood. Basically, clotting occurs randomly throughout the body, as opposed to just in the localized areas where vascular damage has occurred, consuming clotting factors and other components such as platelets in the process. Symptoms may range from a mild bleed, to severe, profuse bleeding, primarily dependant upon the availability of clotting factors. As more and more coagulation factors and components are consumed, the disorder progresses and symptoms worsen. Most heavily impacted are the levels of factors I, V, and VIII as well as the number of available platelets. Clinically, DIC is detected via an elevated (positive) FDP, positive D-dimer test, a prolonged PT and APTT, plus the manifestation of hemorrhagic episodes. DIC is diagnosed as two primary types, acute and chronic. Acute DIC manifests in a few hours or a few days, has a high mortality rate, and is seen in infections, obstetric complications, liver disease, and tissue injury. Chronic DIC is a secondary condition to some other disease state. Once you treat the primary disease, this type of DIC will go away. Treatment is often factor replacement therapy through the use of fresh frozen plasma and/or cryoprecipitate. | View Page |
| Coagulation Disorders and Liver Disease The liver is the site of production for the vast majority of our clotting factors. Therefore, impaired liver function could adversely affect these hemostatic proteins. Some early indicators of a potential liver problem include: An increase in factor VIII. It is not produced in the liver and will be present in elevated numbers as the body attempts to compensate. The PT is sensitive to liver function, so an unexpected, prolonged PT should be evaluated. A lack of fibrinogen is often indicative of severe liver disease. It is difficult to treat liver disease, so therapy typically centers around replacing the missing factors by way of administration of fresh frozen plasma. | View Page |
| Which of the following statements regarding coagulation disorders is incorrect? | View Page |
| Anticoagulation Therapy - Heparin Therapy The use of heparin is prophylactic. It is used either to prevent thromboembolism (a condition in which a blood clot forms inside a vessel), or used to limit a previous thromboembolism. Heparin inhibits thrombin. The degree of inhibition is dosage dependant. Low doses of heparin inhibit initial thrombin formation in the coagulation cascade, and act to slow down overall thrombin generation. At higher doses, heparin can inhibit thrombin entirely, making blood coagulation impossible. Heparin is a potent anticoagulant. Accurate monitoring is essential. The activated partial thromboplastin time (APTT) and/or activated clotting time is used to monitor unfractionated heparin therapy. | View Page |
| Anticoagulation Therapy - Oral Anticoagulant Therapy The therapeutic use of oral anticoagulants is typically the long-term solution for the patient in terms of managing situations of thrombosis. Warfarin, a dicumarol derivative, is one of the most popular oral anticoagulants used today. While heparin is administered intravenously and acts to inhibit thrombin, warfarin is given orally, taken in pill form, and functions as a Vitamin K antagonist. In earlier discussions, it was mentioned that certain clotting factors are considered to be vitamin K dependant. They require vitamin K molecules for their action to occur. Vitamin K dependant factors include factor II, VII, IX, and X. Vitamin K dependant metabolic processes involved with these coagulation factors are inhibited by drugs such as warfarin. The chemical structure of warfarin and similar anticoagulants enables them to bind competitively with free vitamin K. The prothrombin time (PT/INR) is used to monitor oral anticoagulant therapy. | View Page |
| Warfarin cont. The genes involved in warfarin metabolism are CYP2C9 and vitamin K epoxide reductase complex subunit 1 (VKOR). Warfarin owes its anticoagulant action to its inhibition of VKOR. This enzyme recycles vitamin K, a critical element for the clotting factors II, VII, IX, and X, as well as for proteins C, S, and Z. There are six CYP2C9 alleles that are known to cause prolonged metabolism of warfarin: CYP2C9 *2, *3, *4, *5, *6, and *11. (Polymorphisms in CYP450 genes are denoted with asterisks.)One-third of the patients that receive warfarin metabolize it differently than expected and experience a higher risk of bleeding.Genetic testing for the two most common polymorphisms (CYP2C9*2 and *3) as well as for VKOR may be able to reduce the variability associated with warfarin dosing response. Labs performing PGx testing can provide general warfarin dosing recommendations based on the patient's genotype analysis. The lab report will indicate whether a patient has a normal, mild, moderate, high, or very high sensitivity to warfarin. For example, a patient who has one CYP2C9 normal wild-type allele (CYP2C9 *1), one polymorphism (CYP2C9*3), and also a VKOR polymorphism is predicted to have a moderate sensitivity to warfarin. This patient should have frequent INR monitoring and possible warfarin dose reduction. It is important to recognize that knowing a genotype does not necessarily guarantee accurate dose prediction; other drugs and/or environmental or disease factors can also alter CYP2C9 activity. Therefore, monitoring the INR is still very important. | View Page |
| What could have caused the clotting? | View Page |
| Discussion Clotting of blood specimens may be caused by several factors. Clotting usually occurs due to improper phlebotomy technique,and clotted specimens will generally be rejected for those tests that require the blood to be mixed with an anticoagulant. When a clot forms in a tube containing anticoagulant, it usually indicates that the blood and anticoagulant aren’t in proper balance. That is why it is crucial to invert tubes with anticoagulant almost immediately after collection to ensure proper mixing of blood and anticoagulant. Relevant topics: Lavender top tubes, Light blue top tubes, Unsatisfactory specimens: Clots, Causes of clotting | View Page |
| Discussion Tubes are drawn in a specific order to avoid the possibility of erroneous test results caused by carryover of an additive from one tube to the next. If a blood culture is ordered, it should be drawn as the first tube. Additional tubes should follow this order of draw. Sodium citrate - coagulation tube (light-blue top) Serum tube - with or without clot activator or gel. This tube is either a red top tube or a gold top tube depending on manufacturer and tube additive. Sodium or lithium heparin with or without gel plasma separator (green top) Potassium EDTA (lavender or pink top) Sodium fluoride, and sodium or potassium oxalate (gray top) | View Page |
| Lavender top tubes Contain anticoagulant Ethylendiaminetetraactic acid (EDTA) to prevent clotting.
Are used mostly for hematology studies.
Must be completely filled to assure a correct anticoagulant to blood ratio.
Must be inverted after filling to assure proper mixture of anticoagulant with blood.
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| Blood collection tubes: types Rubber stoppers of blood collection tubes are color coded.
Each type of stopper indicates a different chemical additive (usually an anticoagulant to prevent clotting), or a different tube type.
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| Light blue top tubes These tubes contain the anticoagulant sodium citrate.
They are used mostly for coagulation (clotting) studies.
They must be completely filled to assure proper ratio of anticoagulant to blood.They must be inverted immediately after filling to prevent clotting.
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| Causes of clotting Clotting can be caused by: Inadequate mixing of blood and anticoagulant within the collection tube.Delay in expelling blood within a syringe (which contains no anticoagulant), into a collection tube with anticoagulant. | View Page |
| Plasma proteins Numerous types of proteins are dispersed in the plasma. These include:
Coagulation proteins (blood clotting factors), which, if activated, will form a blood clot , and
Serum proteins, which are left dispersed in liquid after the clot is formed. Serum proteins include:
Albumin, a marker of nutrition, and
Globulins, or antibodies. | View Page |
| Pre-analytical Errors Preanalytical Error What is it? How does it happen? What is the result? Hemolysis Red blood cells (RBCs) break and release contents of cell into plasma. Needle incorrectly positioned in vein; cells forced to squeeze through opening. Needle gauge too small; slow blood return into tube. Vigorous mixing or shaking of tube. Alcohol on skin that has not had sufficient time to dry. Some test results may be falsely elevated. (Potassium is especially affected by hemolysis.) Patient may have to be re-drawn. Clotted specimen Clumped or clotted cells in specimen that requires anticoagulated or whole blood Insufficient mixing of blood with anticoagulant in tube. Delay in mixing tube. Slow filling tube. Inaccurate test results for cell counts and clotting studies. Patient may have to be re-drawn. Tube filled to incorrect volume Too little or too much blood in tube. Tube removed from needle too quickly. Vacuum in tube has been compromised due to use of tube past the expiration date (Results in a short fill). Manual fill of tube may lead to over-fill. Test results may be unreliable due to dilution errors. Patient may have to be re-drawn. | View Page |
| Blood Tube Labeling Information Each tube used for blood collection is labeled by the manufacturer with important information. This information includes: tube volume in milliliters (mL), expiration date, lot number and, if applicable, the type of additive that is in the tube. Tube volume: Each tube contains a vacuum that allows a specific amount of blood to enter the tube. In a tube that contains an anticoagulant, the amount of blood that is drawn into the tube will establish the correct blood to anticoagulant ratio. Tubes not filled to the correct volume (over-filled or under-filled) may cause inaccurate test results. Expiration Date: An expiration date is stamped on all blood collection tubes. The tube manufacturer determines this date based on its studies of vacuum maintenance and anticoagulant effectiveness. The expiration date should be checked routinely; tubes that are past the expiration date should be discarded.If a blood collection tube is used past its expiration date, the vacuum may not draw the amount of blood needed to fill the tube completely. Short-filled tubes may not be acceptable for testing and the specimen would have to be recollected. If the tube contains an anticoagulant, it may not work effectively (may not prevent the blood from clotting). Lot Number: A lot number listed on the tube identifies a specific group of tubes that were manufactured at the same time. This information is important to know if a problem is identified with several collection tubes. If the defective tubes are all part of the same lot number, the manufacturer should be notified for replacement of the tubes. Additive: Most blood collection tubes contain a type of additive or chemical that, when mixed with the blood, will yield a specimen acceptable for testing. The various types of additives that are contained in blood collection tubes are discussed on the following page. | View Page |
| Blood Collection Tubes Most blood collection tubes contain an additive that either accelerates clotting of the blood (clot activator) or prevents the blood from clotting (anticoagulant). A tube that contains a clot activator will produce a serum sample when the blood is separated by centrifugation and a tube that contains an anticoagulant will produce a plasma sample after centrifugation. Some tests require the use of serum, some require plasma, and other tests require anticoagulated whole blood. The table below lists the most commonly used blood collection tubes. Tube cap color Additive Function of Additive Common laboratory tests Light-blue 3.2% Sodium citrate Prevents blood from clotting by binding calcium Coagulation Red or gold (mottled or "tiger" top used with some tubes is not shown) Serum tube with or without clot activator or gel Clot activator promotes blood clotting with glass or silica particles. Gel separates serum from cells. Chemistry, serology, immunology Green Sodium or lithium heparin with or without gel Prevents clotting by inhibiting thrombin and thromboplastin Stat and routine chemistry Lavender or pink Potassium EDTA Prevents clotting by binding calcium Hematology and blood bank Gray Sodium fluoride, and sodium or potassium oxalate Fluoride inhibits glycolysis, and oxalate prevents clotting by precipitating calcium. Glucose (especially when testing will be delayed), blood alcohol, lactic acid | View Page |