Ongoing monitoring of heparin anticoagulation is an essential component of many cardiothoracic and vascular surgical procedures in order to prevent significant thrombotic and hemorrhagic complications. The classic test to assess high-dose (>1 unitlmL) heparin anticoagulation is the activated clotting time. Although simple to perform, the activated clotting time has many variations and can be affected by a number of nonanalytical and patient-related factors. Correlation with the heparin concentration may be poor. Alternatively, other test systems assess the individual patient's responsiveness to heparin in order to customize the heparin administration and subsequent protamine neutralization. The choice of test and system depends on the clinical application and the desired outcome. Regulatory and accreditation standards govern this type of testing; modern instrumentation can facilitate compliance with these standards. Understanding of the nature of the test and its performance under a variety of conditions is critical for proper interpretation.
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