- P T INR NORMAL RANGE SERIAL
- P T INR NORMAL RANGE ACTIVATOR
Variables that may affect either PT or aPTT.
P T INR NORMAL RANGE SERIAL
Prepared by measuring clotting time of serial dilutions of normal plasma with saline. Saline dilution curves help describe level of combined factor deficiencies, at which a clotting time prolongs. Some reagent manufacturers provide lot level information about factor sensitivity in PT and aPTT package inserts. Determination of factor sensitivity of PT and aPTT reagents is considered a best practice but is not a required study under Clinical Laboratory Improvement Amendments (CLIA). aPTT heparin therapeutic range represents aPTT values in seconds corresponding to UFH anti-Xa activity between 0.3 and 0.7 IU/mL. Heparin therapeutic range determined by measuring aPTT and UFH anti-Xa activity on a set of at least 20 plasmas from patients treated with UFH ( Semin Thromb Haemost 2017 43:253). Must determine heparin therapeutic range if aPTT will be used to monitor unfractionated heparin (UFH). Must input new mean normal prothrombin time into instrument or LIS for calculation of INR when new lot put into use. Must determine mean normal prothrombin time and input this into instrument or laboratory information system (LIS) for calculation of INR when new lot put into use. Considerations when validating new reagent lots ( Lab Med 2017 48:295, Clin Lab Med 2009 29:253). aPTT reagents differ in contact activator, phospholipid type and phospholipid concentration. PT reagents differ in phospholipid concentration and source as well as source of tissue factor. Reagents used for PT and aPTT testing vary between labs and show different factor sensitivities. aPTT measures effects of factors in intrinsic and common pathways. P T INR NORMAL RANGE ACTIVATOR
aPTT: a contact factor activator (e.g., kaolin, silica) combined with phospholipid and calcium chloride are added to the sample to initiate clotting. Lower International sensitivity index values correlate with more vitamin K antagonist sensitive reagents. International sensitivity index reflects the sensitivity of a PT reagent to deficiencies of vitamin K dependent factors. Scope of study required not practical for clinical laboratories. 
International sensitivity index = slope of the orthogonal regression line derived from comparison on logarithmic axes of PT results for local versus reference method on fresh plasma samples (20 normal plasmas and 60 plasmas from stably anticoagulated patients on vitamin K antagonists).
International sensitivity index determination.International sensitivity index (ISI) is an experimentally derived value that is typically determined by a manufacturer for specific instrument / reagent combinations ( CLSI: H47-A2 - One-Stage Prothrombin Time (PT) Test and Activated Partial Thromboplastin Time (APTT) Test, 2nd Edition, 2008).PTnormal is the geometric mean PT (mean normal prothrombin time, MNPT) determined from a group of at least 20 normal plasmas from healthy individuals including males and females.PTpatient is the measured PT of the patient in seconds.INR is a calculated value to allow for comparison of PT results from different laboratories or reagent lots ( Semin Thromb Hemost 2014 40:195).PT measures effects of factors in extrinsic and common pathways.PT reagents also contain heparin neutralizers (up to 2 U/mL) ( Mayo Clin Proc 2007 82:864).PT: thromboplastin (tissue factor combined with phospholipid) and calcium chloride are added to the sample to initiate clotting.PT and aPTT results are reported in seconds.Centrifuged at 1,500 x g (3,000 RPM) for 15 minutes to separate out plasma that contains Whole blood sample for testing: platelet poor plasma in 3.2% sodium citrate (collection tube with light blue top).Coagulation analyzers use 1 of 2 strategies for clot detection.PT and aPTT are clot based coagulation tests measuring time to formation of fibrin clot ( Lab Med 2017 48:295).Clinical & Laboratory Standards Institute (CLSI) H47-A2 includes general guidance for the performance of PT and aPTT ( CLSI: H47-A2 - One-Stage Prothrombin Time (PT) Test and Activated Partial Thromboplastin Time (APTT) Test, 2nd Edition, 2008).
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