PT, PTT, FIB, INR by ACL 7000
|Author: Penny Stevens |Document Number: |Equ21-01 |
| |Effective (or Post) Date: |13-Jan-09 |
|Review History |Date of last review: |10-Feb-20 |
| |Reviewed by: |Heidi Hanes |
|SMILE Comments: This document is provided as an example only. It must be revised to accurately reflect your lab’s specific |
|processes and/or specific protocol requirements. Users are encouraged to ensure compliance with local laws and study protocol |
|policies when considering the application of this document. If you have any questions contact SMILE. |
Copy _____ of ___ Effective Date:
HEMATOLOGY SECTION
G. COAGULATION
G.1. ACL 7000 ANALYZER - PROTHROMBIN TIME (PT), ACTIVATED PARTIAL THROMBOPLASTIN TIME (APTT) AND INR TESTING
G.1.1. PRINCIPLE:
1. The ACL 7000 analyzer is a fully automatic microcomputer-controlled, microcentrifugal instrument capable of performing the following tests:
1.1. PT-FIB (Prothrombin Time and Fibrinogen Level).
1.2. APTT (Activated Partial Thromboplastin Time).
1.3. PT-FIB/APTT (all three tests run simultaneously).
1.4. D-dimer.
1.5. Thrombin Time
1.6. Single Factors (II, V, VII, VIII, IX, X, XI, XII).
2. The ACL 7000 methodology utilizes spectrophotometry, which is based on the change of light scatter associated with the formation of a fibrin clot. The ACL method is not influenced by inhibitors and will reflect the true fibrinogen concentration
3. The following tests are performed at this hospital: PT (Prothrombin Time) - INR and APTT (Activated Partial Thromboplastin Time).
4. The Prothrombin Time (PT) test evaluates the extrinsic and common pathway of clotting which involve factors II, V, VII, and X.
4.1. The PT is performed by adding a source of tissue extract (typically from brain or lung) to the control or patient plasma, then adding an excess of calcium and measuring the time for clot detection optically.
4.2. The PT test is commonly used for the monitoring of coumadin drug therapy.
4.3. Common causes of a prolonged PT test are vitamin K deficiency, liver disease, specific coagulation deficiencies, Disseminated Intravascular Coagulation (DIC), circulating anticoagulants, presence of fibrin (or fibrinogen) split products, some dysproteinemias, and oral anticoagulant therapy.
5. The activated Partial Thromboplastin Time (aPTT or PTT) evaluates the activity of the coagulation factors involved in the intrinsic coagulation system which involves factors VIII, IX, XI and XII.
5.1. The PTT test is performed by adding a standardized phospholipid preparation as a platelet substitute (an activator) to the control or patient plasma, then adding an excess of calcium and optically measuring the time for clot detection.
5.2. The PTT test is commonly used for monitoring heparin drug therapy.
5.3. The PTT will be prolonged by intrinsic pathway factor deficiencies or by inhibitors, such as lupus anticoagulants, directed against the involved factors or complexes.
5.4. The PTT is also used to monitor low molecular weight heparin using Factor Xa. This test is sent to Bioscentia.
6. International Normalized Ratio (INR):
6.1. The ratio of the patient PT time to that of the geometric mean PT of the normal reference range is useful in monitoring patients receiving oral anticoagulant therapy. However, different thromboplastins exhibit different sensitivities. Therefore, the PT ratio is affected by the reagent used and the method of clot detection. As a result, the INR was developed to improve the consistency of oral anticoagulant therapy. An international reference thromboplastin reagent has been developed for use in standardizing the PT ratio. Manufacturers of thromboplastins calibrate each lot number of this reagent against the standard WHO (World Health Organization) thromboplastin reagent. The results of this calibration are used to develop the International Sensitivity Index (ISI) for each lot of reagent. This number allows for calculation of the INR, which is calculated as follows:
6.1.1. INR EQUATION:
ISI
Patient PT expressed in seconds
INR =
Geo. Mean PT of Normal Reference Range
Expressed in seconds
6.1.2. “Patient PT expressed in seconds” is the PT as resulted by the ACL.
6.1.3 Geo. Mean PT of the Normal Patient Reference Range expressed in seconds is determined by our normal reference interval. This number is a constant that changes only if a new reference interval is established.
6.1.4 The ISI is provided by the thromboplastin reagent manufacturer. This value can be found on the package insert for the reagent and is lot specific. The ISI will change with each lot of reagent.
2. ACL 7000 Ratio Factor:
6.2.1 The ACL 7000 analyzer automatically calculates the INR value. However, in order for the calculation to be accurate, an INR ratio factor must be calculated and entered into the ACL. If the ratio is not calculated and input into the ACL, the geometric mean from the 100% point of the PT calibration curve will be used as the denominator in the INR calculation. This will result in a denominator change with every PT reagent calibration.
6.2.2. ACL INR ratio factor calculation:
(PT Calibration Geo. Mean)/ (Geo. Mean of Ref. Range PT) = ACL INR Ratio
6.2.2.1. The PT Calibration Geo. Mean is the geometric mean of the 100% point of the PT calibration curve.
6.2.2.2. The Geo. Mean of the normal patient reference range PT is currently 11.7. This value will change only if a new normal reference interval is established.
6.2.3 ACL INR ratio factor entry: Once the ratio has been calculated, it must be entered into the ACL through the following menus:
6.2.3.1. Press the PROG key and press the “(” or “(” keys to select SET UP and press ENTER.
6.2.3.2. Select RATIO ADJUSTMENT and press ENTER. Press “(” to continue.
6.2.3.3. Enter the ratio as calculated above (7.2.2) for PT and press ENTER. Do not change the values entered for APTT or TT. Both values must remain at 1.0. Press “ ................
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