The measurement of heparin anti-Xa activity is used to test the plasma levels of heparin in patients treated with unfractionated (UFH) and low molecular weight heparin (LMWH).
Typical heparin (unfractionated, UFH) and low molecular weight heparin (LMWH) are anticoagulants commonly used to reduce the risk of venous or arterial thrombosis. Overdose with these drugs may increase the risk of bleeding while inadequate dosage reduces the effectiveness of anticoagulation. These drugs act as anticoagulants enhancing the ability of plasma antithrombin to bind and inactivate the serine proteases XIIa, XIa, IXa, Xa, and thrombin. Therapeutic follow-up is due to the wide variation in patients' responses to this treatment.
Previously, heparin levels were monitored using the activated partial thromboplastin time (APTT) test. However, a large number of conditions can complicate the use of APTT in monitoring UFH heparin therapy. These situations are divided into three groups. The first group of factors includes those that affect the bioavailability of heparin. Aging, obesity, changes in heparin-binding proteins, presence of liver or kidney disease, and resistance to heparin, fall into this category. The second group of factors includes those that alter the response of APTT to heparin. Increased factor VIII or fibrinogen levels, decreased levels of antithrombin or mildly reduced other coagulation factors (as may occur in the early stages of a coagulation disorder or in oral anticoagulant therapy) are examples of complicating factors in the use of APTT. The third group of factors is the factors that tend to cause prolonged APTT in the absence of heparin treatment, such as, for example, lupus anticoagulant or defective contact agents, which can create a prolonged initial APTT value. In all these cases, heparin anti-Xa activity is the most appropriate method for monitoring heparin therapy.
APTT should not be used to monitor low molecular weight heparin (LMWH) therapy, as this drug does not significantly affect APTT.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
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