Procedure

Procedure

Activated Clotting Time of Whole Blood on the Hemochron Response

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Pediatric Intensive Care

Pathology Department

PRECAUTION: WHILE PERFORMING THIS PROCEDURE, THE FOLLOWING

SAFETY MEASURES MUST BE TAKEN: GLOVES MUST BE WORN; SMOKING, EATING, DRINKING, APPLICATION OF COSMETICS, AND MANIPULATION OF CONTACT LENSES ARE PROHIBITED IN ALL TECHNICAL WORK AREAS. REFER TO THE UNIVERSAL PRECAUTIONS POLICIES.

Complexity: Moderate

I. Method:

The activated clotting time (ACT) is measured with the Hemochron Response instruments. The ACT test is commonly used for heparin anticoagulation monitoring during bypass surgery, neonatal Extracorporeal Membrane Oxygenation (ECMO), hemodialysis, radio frequency ablation, and critical care.

II. Principle:

Heparin therapy is essential in maintaining hemostasis during certain procedures such as bypass surgery; its administration poses significant risk to the patient. Heparin may vary twelve-fold in both patient sensitivity and the rate at which it disappears from the blood. Overdosing heparin can result in dangerous bleeding, while under dosing can lead to thrombosis.

The ACT is a test in which fresh whole blood is added to a test tube containing an activator (celite glass particles or kaolin) and timed for the formation of a clot. The particular clotting activator that is used influences the time required for clot formation. Celite is the standard ACT reAgent used for high level heparin monitoring because of its excellent activating properties. However, serine protease inhibitors such as aprotinin that may be administered to certain patients to decrease postoperative bleeding can prolong the celite activated ACT. When aprotinin is on-board, a kaolin-activated ACT tube should be used.

The Hemochron Response is a portable, battery operated instrument designed to perform whole blood coagulation tests. The Hemochron clot detection mechanism consists of a precision aligned magnet within a test tube and a magnetic detector located within the test well. When a test tube is inserted into the well, the magnetic detector senses a magnet within the test tube as the tube slowly rotates. When the clot begins to form, it causes the magnet to lift within the tube. Since the magnet has been displaced, it is no longer sensed by the instrument's magnetic detector. The instrument gives an audible beep and displays the coagulation time.

III. Materials:

Syringes for sample collection:

Tuberculin syringe with no anticoagulant

One of the following test tubes:

§ CA510 (black flip-top) - store at room temperature - No expiration date.

§ P214/P215 (clear plastic flip-top) - store at room temperature - No expiration date.

IV. Specimen Collection and Handling:

Prior to collecting the patient’s sample, the patient’s identity must be verified by looking at the arm band. Obtain blood specimen. Adhere to the appropriate technique below:

A.(CA510):

Indwelling venous blood line:

NOTE: Do not obtain blood from heparinized access line, lock or indwelling heparin lock.

§ Discontinue fluids drip, if required.

§ Use a two-syringe technique -perform a 5 cc draw and discard the first syringe. Obtain a 3 cc sample with the second syringe for testing.

Extracorporeal blood line port:

§ Flush the extracorporeal blood access line by withdrawing 5 cc of blood then obtain a 3 cc sample with a second syringe for testing.

Venipuncture:

§ Use a two-syringe technique and discard the first 2 cc draw. Obtain a 3 cc sample with the second syringe for testing.

Vacuum Draw:

§ Perform venipuncture maintaining the arm in its downward position.

§ Push tube to the end of the holder and pierce the top of the tube. The contents of the tube should not come in contact with the needle or stopper to prevent the possibility of backflow from the tube.

§ Remove the tourniquet once blood begins to flow into the tube.

§ The appropriate blood volume has entered the tube when the blood flow into the tube ceases.

B.(P214/P215):

Draw 0.4 ml blood sample from a previously flushed extracorporeal line using a 1 cc tuberculin syringe. Make certain that the blood sample is representative (do not take sample from a line through which heparin has been administered).

Extracorporeal blood line port:

§ Flush the extracorporeal blood access line by withdrawing 3 cc of blood.

V. ACT Procedure:

1. Press MENU 1 or MENU 2 (depending on the well to be used for the test) once. The first page of the main menu is displayed.

2. Press 2. The QC Selections menu is displayed.

3. Press 4. A prompt will confirm a patient test is being run:

“Patient Test”

4. Dispense the sample into the test tube (see directions below for specific test tube being used)

5. Insert tube into test tube well

6. Press START 1 or START 2. A beep will signal the start of the test and timing of the test begins.

7. Enter Operator ID when prompted

8. Enter Patient ID when prompted

(CA510)

1. From the collection syringe dispense exactly 2.0 ml of blood into the test tube. At the same time, press START 1 or START 2 as blood first appears in the tube.

2. Close the flip-top. Immediately agitate the test tube vigorously from end-to-end ten times to disperse the activator.

3. Insert test tube into the Hemochron test well. The tube is rotated automatically in the well until clot formation is detected.

4. When clot formation is detected, the instrument beeps three times and the test name, clotting time (in seconds) is displayed. The results of the test will be displayed until CANCEL, START 1, or START 2 is pressed.

(P214/P215):

1. Before drawing the blood sample, hold test tube vertically and tap the tube bottom several times on a horizontal surface to shake activator particles down into testing zone.

2. Flip open the cap of the Hemochron plastic test tube and dispense 0.4 ml of blood into the test tube. At the same time, press START 1 or START 2 as blood first appears in the tube.

3. Close the flip-top. Holding the test tube in an upright position with thumb and forefinger, mix blood and activator by gently flicking the bottom of the tube with remaining fingers.

4. Insert test tube into the Hemochron test well. The tube is rotated automatically in the well until clot formation is detected.

5. When clot formation is detected, the instrument beeps three times and the test name, clotting time (in seconds) is displayed. The results of the test will be displayed until CANCEL, START 1, or START 2 is pressed.

VI. Quality Control:

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

Materials Needed:

§ Hemochron Whole Blood Liquid Controls:

§ Hemochron Instrument

§ Plastic syringe (5 cc) with 20 or 21 gauge needle

§ Hemochron Coagulation test tubes

§ Electronic System Verification Tube

A. Whole Blood Quality Control:

1. Handling and Storage:

Whole Blood controls are stable until the marked expiration date when stored at 4-8°C. Room temperature storage is possible for non-punctured vials; room temperature dating is to a maximum of seven weeks, but must never exceed the marked expiration date.

Note: If kept refrigerated, allow all quality control and coagulation test vials and/or test tubes to first reach room temperature and then stabilize for at least 20 minutes before use. This may take up to 60 minutes.

2. Frequency:

If Electronic QC’s are not used, two levels of quality control (normal and abnormal) must be performed every 8 hour shift 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.

If Electronic QC’s are used, two levels of whole blood QC are used to validate each box of ACT test tubes. Once a box is validated for use, print or affix a “VERIFIED” label on the outside of the box.

3. Whole Blood Quality Control Test Procedure:

a. Press MENU 1 or MENU 2 (depending on the well to be used for the test) once. The first page of the main menu is displayed.

b. Press 2. The QC Selections menu is displayed.

c. Press 1 or 2, corresponding to whether a normal or abnormal control is being run. The QC Ranges menu for the selected control level is displayed

d. Press YES if correct. (If the current limit is not correct, press 1, 2, or 3 depending on what needs to be changed. The current limit or lot number is displayed. A flashing cursor is positioned where the first character of the new lower limit or lot # is to be entered. If needed, enter the new value and press YES.)

e. Dispense the control sample into the test tube as described below under “Dispensing of liquid QC into the tube.”

f. Press START 1 or START 2. A beep will signal the start of the test, and timing of the test begins.

g. Mix the contents of the control test tube and place the tube in the test tube well. The tube is rotated until clot formation is detected.

h. If the results pass, the instrument will display:

“Acceptable”

“Remove Tube”

And routine testing can continue.

i. If the results are unacceptable, the problem must be resolved and controls run successfully before patient testing can be performed.

Dispensing of Liquid QC into the tube:

a. Peel back the flip top on the distilled, deionized water vial, but do not remove the crimp seal (use this technique when opening each vial). Using a 5 cc plastic syringe with needle, withdraw exactly 2 cc from the distilled, deionized vial and transfer into the plasma vial by direct puncture of the stopper.

b. Using moderate end-to-end inversion, agitate the plasma vial for 30 seconds to achieve rehydration. Avoid excessive agitation which will cause foaming of the plasma. Verify complete rehydration of the control visually.

c. Allow the plasma to stabilize for 60 seconds.

d. While the plasma is stabilizing, use the same syringe and needle to withdraw exactly 1 cc from the calcium chloride vial.

e. After 60 seconds, transfer 1 cc of calcium chloride into the plasma vial by direct puncture of the stopper. Do not remove the syringe and needle from the vial.

f. Firmly holding the syringe in place, vigorously agitate the vial

approximately four to six times.

g. Using the syringe already in place, withdraw the correct amount of the mixture for transfer into the appropriate Hemochron test tube:

CA510- 2 cc

P214/P215- 0.5 cc

h. For CA510 test tubes: Transfer the 2 cc into the Hemochron test tube. Vigorously agitate the tube four to six times.

For P214/P215 test tubes: Transfer 0.5 cc into the Hemochron test tube. Holding the tube vertically, flick the tube 4 to 6 times.

4. Troubleshooting:

If quality control does not fall within the acceptable limits the following steps should be taken:

a. Verify that the quality control materials and test tubes are within expiration date. Check tubes for cracks and adequate activator. Verify that the controls and reagents are stored correctly. Verify operator technique. Repeat test using fresh control material.

b. If test is still out-of-limits, perform weekly maintenance and repeat control.

c. If control remains out-of-limits, DO NOT USE INSTRUMENT, put a sign on instrument stating that it is out of order. Contact Pathology department for further assistance (Point of Care Medical Technologist ext. 4431 or pager #4431). Use a backup instrument until problem is resolved (see page 2 for list of instruments and locations).

d. Document all corrective actions on the quality control log.

B. Electronic Quality Control:

1. Handling and Storage:

The Electronic System Verification Tube is stored at room temperature. It is reusable and has no expiration date.

2. Frequency:

Two levels (normal and abnormal) are used every eight hour shift of patient testing. The normal level is a 100 second QC tube. There are two abnormal levels. Those areas using CA510 tubes will use the 500 second abnormal QC tube and those using P214/P215 tubes will use the 300 second QC tube.

3. Electronic Quality Control Test Procedure:

a. Press START 1 or START 2 (depending on the well to be verified) to begin a test on a well. A beep will signal the start of the test. At the same time the START button is pressed, press the 100 second button on the Electronic System Verification tube.

b. Insert the electronic QC tube into the test well.

c. Enter the four digit Operator ID and press YES

d. Enter the serial number of the ESV tube (The serial number is located on the back of the ESV tube.)

e. At the completion of the test, the result is automatically printed

f. Repeat the test, using the 300 or 500 second button for the first well. Then, repeat the entire test on the second well.

The test results are acceptable if all of the results are within 10 seconds of

the selected time.

NOTE: If the barcode label of the ESV tube is not read, display the QC Selections menu by pressing MENU 1 or MENU 2 (depending on the well to be used for the test) once to display the first page of the main menu and then pressing 2. Select 3 and enter the ESV serial number.

4. Troubleshooting:

If quality control does not fall within the acceptable limits the following steps should be taken:

a. Repeat ESV Tube.

b. If a fault message is illuminated next to the test result, the battery in the verification tube is nearly depleted and should be replaced.

The verification tubes require 2 “AA” batteries.

VII. Maintenance:

Document all maintenance performed on monthly maintenance sheet.

A. Weekly:

1. Inspect and clean the test well and test tube drive collar of residual dried blood or other foreign matter. Use a cotton swab moistened with a 10% bleach solution. Remove all moisture with dry cotton swab after cleaning.

2. Verify that heater light is lit.

B. Every 6 months:

Check function of incubator. This can be performed by any operator or a Medical Technologist. The temperature of the test wells is verified using the Hemochron Temperature Calibration Test Tube.

a. Press MENU 1 or MENU 2 (depending on the well to be tested) and then press 3. The Prewarm Menu is displayed.

b. Press 5. Prewarming commences and the elapsed prewarming time of t 500 seconds is displayed.

c. Insert the Temperature Verification Tube into the test well.

d. When 0 seconds is displayed, read the thermometer in the well.

e. The temperature of each well should be 37± 1.0 °C. If temperature is not within limits, contact the Pathology department.

f. Repeat the test for the second well.

Check function of timer against a stopwatch.

VIII. Quality Assurance:

Quality control results and maintenance is reviewed weekly by a Medical Technologist. Quality assurance reports are completed and distributed monthly to each testing area for review.

IX. Limitations:

The Hemochron ACT tests are affected by poor technique, including specimen collection and test procedure. Inadequate specimen/reagent mixing may result in reduced precision and accuracy. Improper storage of test kits may affect results.

The ACT may be affected by hemodilution, cardioplegic solutions, hypothermia, platelet dysfunction, hypofibrinogenemia, other coagulopathies, and certain medications.

Test results of 600 or more seconds imply a slow rate of fibrin formation. Results greater than 600 seconds should be interpreted qualitatively only. Results of 80 seconds or less generally indicate improper instrument starting technique.

A test is terminated and operation of the test well automatically shuts off if clot formation is not detected within 1500 seconds after the test is started. If the instrument terminates a test in this manner, a FAULT-1500 message is displayed indicating the test result is outside of the specified range.

X. Expected Values:

The reference range for ACT is to be established by each patient care area. Generally, a baseline is taken before heparin is given. The ACT is then expected to increase after the dose is given

This increase depends upon how large the dose is and the duration of the procedure. All ACT test results are put into the patient’s chart and/or appropriate computer system: Sunquest, CareView, or Siemens Cath-Cor. Critical values are up to the assessment of the physician.

XI. Interpretation of Test Results:

Hemochron test results are quantitative indices of the in vitro rate of coagulability of the blood specimen tested. The results may be interpreted by the clinician as an indication of the status of anticoagulant therapy at the time of sample collection.

XII. Linearity:

The linearity of the ACT test is 80-600 seconds. Results out of the reportable range should be reported as <80 or >600 sec.

XIII. Proficiency Testing:

Proficiency testing will be provided by the College of American Pathologists (CAP). Two specimens will be received three times a year for analysis of activated clotting time.

A passing grade is required to maintain proficiency. Only Hemochron operators may perform PT.

Results will be received and reviewed by the Director of Clinical Pathology. Results will be communicated to each department by the Point-of-Care Medical Technologist via the monthly Quality Assurance reports.

XIV. Competency Checks:

Competency checks are performed on each operator during initial inservice, after 6 months of employment, and yearly thereafter. Observance of incompetency will necessitate re-inservicing and inability to use analyzer until competency is acceptable.

XV. References:

Hemochron Models 401 & 801 Operator's Manual. International Technidyne Corporation. February, 1991.

Hemochron System Instruction and Technical Guide. September, 1983.

Activated Clotting Time by Hemochron CA510/CA510, K-ACT/FTK-ACT, P214/P215, S412, Package Insert. May, 1992.