Prothrombin Time on the Coaguchek Analyzer



Prepared by


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Hematology Department








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CLIA Complexity: Moderate





I.          Method:


The Prothrombin Time (PT) is measured using the CoaguChek System.  When used correctly, this system may be used to monitor the oral anticoagulant (warfarin) level of patients to ensure its level is maintained in the therapeutic range.


II.          Principle:


When a drop of fresh blood is placed on the test strip, the blood is drawn into a reaction chamber and mixed with reagents that start the coagulation process.  Tiny iron particles are also mixed with the test strip sample, and alternating magnetic fields cause the iron particles to move.  The endpoint of the test is reached when the blood clot stops the iron particles from moving.  The monitor then displays the PT result.


III.          Materials


C                   The CoaguChek Monitor with the proper Code Chip installed.  Each Code Chip is specific to a particular lot of test strips.  A Code Chip is inserted into the CoaguChek monitor each time a new box of test strips is opened.  The Code Chip contains programming information about the test type, lot number, expiration date, and function curve.

Storage of Code Chip: The Code Chip must not be exposed to moisture or devices that           produce magnetic fields.

C                   The CoaguChek Test Strips which contains non-human thromboplastin, stabilizers, and preservatives. 

Storage of strips: Strips are stored in the refrigerator (2° to 8°C) until ready for use.  Do not freeze!  When stored at room temperature, test strips are stable for 60 days or until the expiration date, whichever comes first.  Only the number of foil pouches necessary for testing should be removed from the refrigerator.  Allow the sealed pouches to sit at room temperature for at least five minutes before opening for the testing procedure.  The test strip must be used within four minutes after opening the sealed pouch.

C                   Lancets (For capillary sample collection)

C                   Plastic syringes free of anticoagulant (For venous sample collection)

C                   Alcohol wipes

C                   Cotton balls or gauze

C                   Disposable gloves


IV.          Specimen Collection and Handling:


No special patient preparation is necessary.  The patient’s identity must be verified prior to drawing the blood specimen.  This can be done by examining the inpatient’s arm band or the by verbally verifying the patient’s name and date of birth with the patient or parent/guardian. 


Sample size: Minimum of 25ul of blood.

CoaguChek PT tests may be performed with fresh capillary whole blood from a fingerstick or fresh venous whole blood drawn in an anticoagulant-free plastic syringe. 





Criteria for rejecting specimens:


C                   Plasma or serum cannot be used as a testing sample.

C                   Patient cannot be on heparin therapy.  Heparin interferes with the CoaguChek test.

C                   Sample size cannot be less that 25ul.

C                   Venous sample cannot be collected in a syringe containing anticoagulant.

C                   Sample must be used immediately after collection.

C                   Glass tubes or glass syringes may not be used (plastic is acceptable).

C                   Additional blood sample should not be added to the test strip once testing has begun.


V.          Calibration


The Code Chip supplied with each box of test strips automatically calibrates the monitor for that particular lot of strips.  In addition, every time the monitor is turned on, it goes through an automatic diagnostic check.  The user does not need to do additional calibration testing. 


VI.          Quality Control


The quality control products are intended to verify proper instrument and test performance, as well as operator technique.


Materials Needed:

C                   The CoaguChek Monitor with the proper Code Chip installed

C                   The CoaguChek Test Strips which contains non-human thromboplastin, stabilizers, and preservatives.

C                   CoaguChek Liquid Controls

Storage: CoaguChek Liquid Controls are to be stored in the refrigerator (2° to 8°C).  Do not freeze!  If stored in the refrigerator, controls are stable until the manufacturer’s expiration date.  When stored at room temperature, controls are stable for 30 days or the expiration date, whichever comes first. 



Two levels of quality control (normal and abnormal) must be performed every 8 hours on days that patient testing occurs.  Controls should also be run after any maintenance procedures and whenever the patient values do not match the expected results.  It is the responsibility of the personnel performing the patient testing to perform quality control.


CoaguChek Liquid Quality Control Test Procedure:


NOTE: Only the number of controls necessary to perform the test(s) should be removed from the refrigerator.  The controls and test strips need to be brought to room temperature 5 minutes before testing.


1.          Preparation of control solution:

a.  Pull the tab on the control vial to remove perforated seal.

b.  Holding vial upright, tap vial on the tabletop to settle the glass capsule to the bottom              of the vial. 

c.  Squeeze the lower half of the control vial to break the glass capsule.  Use both hands      if necessary.  The capsule must break.  Do not bend the vial.  Bending may cause the      glass to cut through the exterior wall of the plastic vial.  Do not mix contents by         rolling between thumb and forefinger. 

d.  Set a timer for 2 minutes.  Holding the vial upright, immediately tap the vial hard on             the tabletop 10 times to mix reagents.

e.  Set the control aside and do not disturb the vial for the remainder of the 2 minutes.

f.  After the 2 minutes have passed, open the foil pouch and remove the test strip to           begin testing.

2.       Turn the monitor on and ensure proper time, date and operating conditions.  PERFORM           TEST?  Should appear on the display.

3.       Press YES button on monitor.  INSERT STRIP appears on the display.

4.       Insert strip into monitor, printed side up, until the monitor displays IS THIS A                   CONTROL?

5.       Press YES on monitor.  The monitor displays PLEASE WAIT.

6.       After 45 seconds, the monitor will display APPLY SAMPLE.  When monitor displays           APPLY SAMPLE, shake down the contents of the vial toward the dropper end.  Shake           down hard.

7.       Hold the vial dropper-end down and remove the cap.  Save the cap.

8.          Discard the first drop of control solution into the cap.  Discard the cap.

9.       Allow a large, hanging drop of control solution to form from the dropper.  Gently touch drop to the center of the test strip’s yellow sample target area.  The drop must contact the half-moon shaped channel at the top of the target area.  The sample must completely cover the target area.

10.     The monitor displays TESTING along with a progress bar.  During this time, do not           disturb the strip or add more control solution to the strip.

11.     The PT control value is displayed followed by a “C”.  Compare the control value to the           CoaguChek Control Results Sheet.

12.          Record the control value on a quality control log.

13.          Properly discard the used test strip and the control vial.


Acceptable Quality Control Ranges:


Acceptable CoaguChek Liquid Control ranges are found on the CoaguChek Control Result Sheet.


If the quality control test results are outside the acceptable control range, patient testing can not occur until corrected.  All results out of range are to be repeated.  All corrective actions are to be documented on the testing log.  If repeating the control still yields an out of range result, the following corrective action is recommended:




















Make sure strips and controls were stored correctly and have not expired.




Make sure the foil pouch was not opened longer that 4 minutes.




Make sure the control was mixed thoroughly after breaking the glass capsule.




Make sure the control was used within two to four minutes of breaking the capsule in the vial.




Clean the monitor as recommended in the CoaguChek User=s Manual, and repeat the test.




If results are still unacceptable, call Roche-Boehringer Mannheim Technical Service at 1-800-428-4674, 24 hours a day, 365 days a year.


VII.          Maintenance


The interior and exterior parts of the CoaguChek Monitor should be cleaned each time a new Test Kit is opened.  If the monitor becomes contaminated with blood, it should be disinfected with a 10% bleach solution.


Cleaning the interior:


1.       Press the door release and lift the door to the fully opened position.

2.       Clean the test strip guide with a cotton-tipped swab dampened with a 10% bleach           solution. 

3.       Clean the underside of the door with a lint-free wipe. 

4.       Dry the test strip guide and underside of door with a lint-free wipe.  Allow it to air dry for      10 minutes.


Cleaning the exterior:


1.       Wipe the outside of the monitor with a clean cloth slightly dampened with a solution of 1           part bleach and 9 parts water.  Do not flood the monitor.


VIII.          Quality Assurance:


Quality control results and maintenance is reviewed monthly by the Point-of-Care Testing Medical Technologist (or designee).  Quality Assurance reports are completed and distributed monthly to each testing area for review.


IX.      Patient Testing Procedure:


1.       Place the monitor on a flat surface free of vibrations and turn it on.

2.       When PERFORM TEST? appears on the display, press YES.

3.          INSERT STRIP appears on the display.  Open the foil pouch at the tear mark and remove           the test strip.  NOTE: You must use the strip within 4 minutes of opening the foil pouch.

4.       Insert the test strip into the monitor in the direction of the printed arrows, printed side up.  The monitor displays IS THIS A CONTROL?

5.       Press NO.

6.       When APPLY SAMPLE appears on the display, obtain the venous or capillary blood           sample.  (See Specimen Collection and Handling section)

a) Direct capillary application- Apply blood directly from the finger to the test strip.

    NOTE: The first drop of blood should be used.

b) Using a capillary tube- Touch the capillary tube to the drop of blood.  Keep the tube                       level and allow it to fill by capillary action.  Put the finger over the hole in the end of                         the capillary tube.  Hold the capillary tube directly over the sample target and expel                     sample.   NOTE: Avoid getting air bubbles into the sample. 

c) Using a Venous Sample- Expel one to two drops of blood from the syringe needle.                        Then place one drop of blood from the syringe needle directly onto the sample target     area of the test strip.

7.          Completely cover the yellow sample target area.  The sample must contact the upper part of the target area.

8.       A progress bar is displayed to show how much time is left before the test is complete.  All      16 boxes will be filled in when the test is complete.

9.       The result will appear in about 2 minutes.  Document the result in the patient chart.


X.       Patient Results


All results are recorded in the patient’s chart.


The normal range for prothrombin time established here at XXXXXl Hospital is

11.9 to 14.5 seconds. 


The physician should determine the best PT level for the patient depending on the reason for anticoagulant treatment and how each individual responds to treatment.  Each physician should establish expected values for his or her patient population or individual patients. 


Any unexpected result should be followed up with appropriate coagulation studies and inquiries to define the cause of the unusual result.


XI.          Limitations of Procedure


C                   Fresh capillary or venous whole blood should be used on the CoaguChek Monitor.  For capillary samples, the first drop of blood should be used.  Plasma and serum are not acceptable.

C                   Samples are collected using plastic syringes without anticoagulants or additives.  Glass tubes or syringes are not to be used.

C                   The volume of the blood drop must be a minimum of 25ul.  Low sample volume will cause a SAMPLE ERROR-REMOVE STRIP warning.

C                   In rare cases, patients with long clotting times (>9 INR, >36 sec.) may observe test errors.  If test errors persist, results must be confirmed with an alternative test method.

C                   The CoaguChek test measures PT results in persons on warfarin-type (Coumadin) therapy.  This test is not used to monitor persons on heparin therapy.  In vitro studies have shown that the CoaguChek System is sensitive to levels of heparin over 0.15U/mL.

C                   If a patient is on intravenous infusion therapy, the sample should not be collected from the same arm. 

C                   Hematocrit ranges from 32% to 52% do not significantly affect test results.

C                   No interference has been found in lipemic samples containing up to 500 mg/dl of triglycerides.  In tests performed with in vitro-spiked samples, bilirubin up to 20mg/dl and hemolysis up to 500 mg/dl did not significantly affect test results.


XII.          References


CoaguChek System Policies and Procedure.  81997 Boehringer Mannheim Corporation.