Lipp Vis Nursing ChaptLWBK1630_C02_p013-068

16  Chapter 2 • Cardiovascular Care Evaluating Lipid Test Results COAGULATION TESTS

Test

Action

Elevated Levels

Normal Range

International Normalized Ratio (INR)

The INR system was established to reduce the interlaboratory variation in prothrombin time. The INR is calculated as a ratio of the patient’s PT to a control PT obtained using an international reference thromboplastin reagent developed by the World Health Organization (WHO). Assesses the clotting ability of blood. A prothrombin time within this range indicates that the patient has normal amounts of clotting factors VII and X. aPTT is sensitive to the deficiencies or abnormalities of both intrinsic and common coagulation factors, i.e., Factors I, II, V, X, VIII, IX, XI, XII, Fletcher factor, and Fitzgerald factor. The activated partial thromboplastin time (aPTT, PTT) measures the time it takes plasma to clot when exposed to substances that activate the contact factors, which assesses the intrinsic and common pathways of coagulation The thrombin time (TT) measures the final step of coagulation, the conversion of fibrinogen to fibrin Used for monitoring warfarin (Coumadin) treatment.

Increased INR values may indicate disseminated intravascular coagulation (DIC), liver disease, antiphospholipid antibodies,

In healthy people an INR of 1.1 or below is considered normal.

An INR range of 2.0 to 3.0 is generally an effective therapeutic range for people taking warfarin for disorders such as atrial fibrillation or a blood clot in the leg or lung. In certain situations, such as having a mechanical heart valve, you might need a slightly higher INR.

INR is the preferred

vitamin K deficiency, or uncontrolled oral anticoagulation

test and best standardized measurement of PT.

Prothrombin time test (PT)

A prolonged PT time is considered abnormal

11–15 sec

Activated Partial Thromboplastin Time (aPTT)

When the aPTT is prolonged, there is an inhibitor present in patient’s plasma.

29–35 sec

Thrombin Time (TT)

Thrombin time is prolonged in the presence of heparin, hypofibrinogenemia, dysfibrinogenemia, and fibrin degradation product

15–17 sec