Abbrev Code:INR   
Order Code:LAB3572Order Name:INR
Synonyms:Protime; PT; Prothrombin Time; Anticoagulation
Methodology:Electromagnetic clot detection
CPT Codes: 85610 x1
Test Includes:International normalized ratio (INR)
Turnaround Time:Performed and reported 24 hours/day.
Associated Links:

Specimen Collection and Processing for Coagulation Specimens

Collection Instructions

Optimal Volume:2.7 mL (in 3 mL tube) - filled to fill line on the tube
Minimum\Peds Volume:1.8 mL (in 2 mL tube) - filled to fill line on the tube
Container:Blue Na Citrate, 3.2% - fill to fill line on tube
Collection Instructions:If the patient's hematocrit is >55%, contact laboratory to obtain a special tube. If using a butterfly needle, a waste tube must be collected before the blue top.
After Care:If the patient has a coagulation abnormality, apply direct pressure to the puncture site for 10 minutes; apply a pressure dressing. Instruct the patient to leave the bandage on for 12 hours.
Causes for Rejection:Underfilled tubes, overfilled tubes, clotted specimens, specimens collected in 3.8% buffered citrate.
Grand Itasca: Whole blood specimens greater than 24 hours old.
All other Fairview sites: Specimen greater than 8 hours old or not processed appropriately within 8 hours after collection or specimens stored in the refrigerator.

Processing and Shipping

Specimen Processing:Send whole blood or platelet poor plasma. See Associated Link for additional processing instructions.
Shipping Instructions:Whole blood specimens must arrive within 8 hours. If greater than 8 hours is required for transport, follow specimen processing instructions and ship frozen plasma on dry ice.
Test Performed at or Referral Lab Coagulation  (BurnsRidges, Clinics, CSC Maple Grove, CSC Mpls, Grand Itasca, Lakes, Northland, Oxboro Clinic, Range, Ridges, Southdale, St. John's, UMMC East Bank, UMMC/UMMCH-West Bank, Woodwinds)


Critical Range:INR: Greater than 5.0
Grand Itasca (GICH): INR >=5.0
Reference Range:
Less than 30 days 0.81-1.30
1-5 months 0.81-1.17
6 months and older 0.85-1.15
Therapeutic Range:INR 1.5 to 3.5 depends on whether oral anticoagulation is being given prophylactically or for existing thrombosis as well as patient's overall clinical situation, risk of thrombosis. The recommended therapeutic target for most patients is 2.0-3.0. The suggested therapeutic range for inpatients with recurrent thromboembolic events or with additional risk factors in an INR of 2.5-3.5.
Limitations:INR results may be unreliable for patients with lupus anticoagulants or other antiphospholipid antibodies (anticardiolipin and/or anti beta 2 glycoprotein) or concurrent administration of other anticoagulants, such as direct thrombin inhibitors (e.g. argatroban, bivalidrudin and dabigatran). Chromogenic factor X (factor 10) and/or factor ii (factor 2) activity may be used in some patients for monitoring the effects of vitamin K antagonists. Refer to Lab Guide for these tests or contact Special Coagulation Laboratory for consultation at 612-273-4797. INR monitoring of patients on Amiodarone may need to follow an Adjusted Warfarin protocol; contact Pharmacy for details. Due to various factors which influence the INR, method differences between INR performed in the main laboratory and by point of care may lead to differences between the two results.
The International Normalized Ratio (INR) is now the most widely recommended test for monitoring oral anticoagulation because the INR, unlike the prothrombin time (PT), reported in seconds, is largely independent of the specific instrument and reagent used. As is true for the PT, the INR becomes elevated with deficiencies in the extrinsic coagulation pathway clotting factors (fibrinogen and factors 2, 5, 7 and 10). Both the PT and the INR are more sensitive to deficiency of factor 2 than the other extrinsic factors.

Prolongation of the INR may occur in a number of conditions, including factor deficiency, anticoagulants, liver disease, vitamin K deficiency, disseminated intravascular coagulation (DIC), factor inhibitors, lupus anticoagulants and dilution.

Although the INR was originally introduced for monitoring patients on oral anticoagulants, our experience has shown the INR to be just as useful as the PT reported in seconds for evaluating the hemostatic abnormalities in liver disease. Because the INR is far more consistent across laboratories and significantly more consistent long-term within a laboratory, the PT in seconds in not reported.

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