Heme - Hemostasis Testing

No anticoagulant; serum is obtained from these "clot" tubes.

EDTA anticoagulated whole blood used for cell counts.

Contains 3.2% citrate; used for virtually all coagulation testing.

By complexing free Ca++, citrate inhibits clotting since the majority of enzymatic reactions in the coagulation cascade require calcium. These tubes contain 0.5 mL of anticoagulant. The vacuum in the tube is precisely set to draw 4.5 mL of blood.

This measurement is generally performed on an automated particle counter and is very accurate. An estimate of the platelet count can also be made from the peripheral blood smear, although it is really only useful for extremely high or low platelet counts.

The bleeding time measures the time it takes to stop bleeding after a standard cut is made in the skin. It is a measure of the platelet and vascular components of hemostasis. The bleeding time is normal in coagulation factor deficiencies EXCEPT for von Willebrand Disease.

Increased MPV is associated with recurrent coronary syndromes.

An instrument that stimulates and measures in vivo the process of platelet adhesion and aggregation using citrated whole blood. The assay measures the time it takes to occlude a pinpoint hole at the end of a disposable collagen-impregnated membrane under a shear force of 1500 sec-^1. Cartridges are also coated with either ADP or epinephrine to enhance platelet activation. Results are measured as closure time (CT).

Platelet aggregation may be done on whole blood or platelet rich plasma (PRP). PRP is prepared by a low speed centrifugation that pellets leukocytes and red blood cells, but leaves the less dense platelets in the plasma. Aggregation is assessed by incubating PRP with an agonist while stirring the suspension. Using a photo-optical detector, the amount of light transmitted through the suspension is measured. Over time and with increasing aggregation, more light is transmitted. ATP release is measured by a sensitive luminescent assay for extra-cellular ATP.

A deficiency or inhibition of factors VII, X, V, II, and/or fibrinogen.

An abnormally prolonged PT in conjunction with a normal aPTT suggests a deficiency of factor VII.

Ensures that PT results are normalized for the sensitivity of the thrombopastin used, thus eliminating a major cause of variation in PT results between different laboratories.

INR = Patient PT / mean of normal PT

Hemophilia A (factor VII deficiency), hemophilia B (factor IX deficiency), von Willebrand disease, and other congenital or acquired deficiencies of the intrinsic pathway.

A mixture of calcium and thromboplastin, which contains phospholipids and tissue factor (formerly factor III) derived from rabbit brain, is added to citrated patient plasma.

Plasma is recalcified in the presence of a standardized amount of platelet-like phosphatides and an activator of the contact factors of the intrinsic coagulation pathway. A platelet substitute (cephalin or crude phospholipid = partial thromboplastin), a surface-activating agent (actin or kaolin) to activate factor XII, and Ca++ are added to the plasma.

This test is used to determine whether a prolonged PT, aPTT, or dRVVT is due to a factor deficiency or an inhibitor. It is based on 2 main principles: 1, the inhibitor is in excess and if present will inhibit normal and patient plasma, and 2, that 50% of any factor is sufficient to yield a normal test result. Correction into the normal range after mixing indicates a factor deficiency, while no correction suggests the presence of an inhibitor.

Whole blood is drawn into tubes containing a particulate activator of the intrinsic activation system. Exposure of these negatively charged surfaces activates the contact pathway. Clotting times are typically slightly below 100 seconds. Its simplicity and good linearity allow it to be used in a point-of-care manner, so it is often used in the OR. Considered inferior to the aPTT for monitoring heparin therapy.

This measures the conversion of fibrinogen to fibrin and is prolonged by hypofibrinogen, dysfibrinogenemia, heparin, and fibrin degradation products.

It is a functional fibrinogen assay based on the fact that the thrombin clotting time of dilute plasma is inversely proportional to the fibrinogen concentration. The formation of the fibrin polymers is recognized in the laboratory as the clotting time end point of the reaction.

This is an assay for factor XIIIa cross linked dimers of the D fibrin degradation product. Thus, for D-dimer generation there must be activation of both clotting and fibrinolysis.

Factor XIII is a transglutaminsae that covalently cross-links soluble fibrin polymers to form stable, insoluble fibrin. To assay factor XIII, plasma is re-calcified and allowed to clot. The clot is suspended in 5 M urea, which disrupts hydrophobic bonds. Diminished factor XIII results in the lack of covalent bonds between fibrin monomers, such that the clot dissolves.

Antibodies associated with thrombosis, and both are measured by an ELISA.

Measures the direct activation of factor X and is useful in the diagnosis of the lupus anticoagulant. Russell viper venom (RVV) directly activates factor X to factor Xa. It is added to the plasma sample with a platelet substitute (phospholipids), calcium and the clotting time is measured. By directly activating X, RVV bypasses the extrinsic and intrinsic pathways.

The LA confirmation ragent contains concentrated phospholipid. This reagent is added to the test plasma. If a test plasma has a phospholipid dependent antibody, the added phospholipid will absorb the antibody, resulting in shortening of the clotting time.