Whole-Blood Clotting Time & Clot-Retraction Time (Lee-White Coagulation Time; Coagulation Time; Venous Clotting Time)

Advertisement

Category: Hemostasis.
Subcategory: Coagulation tests.
Material studied: Blood.
Estimated cost of test: $10.00.
Patient time for test: 5-10 minutes.
Reliability of test results: Good.
Available as home self-test? No.
Note: Blood-clotting time is based on the number and activity of platelets, fibrinogen, intrinsic-factor levels and hematocrit. Test measures time for fresh whole blood to clot.

Advertise

BEFORE THE TEST

Purpose of test:

• Assesses intrinsic system of blood coagulation.
• Monitors effectiveness of heparin therapy but less accurately than the activated partial thromboplastin time (APTT).

Where is test performed?

• Commercial laboratory, hospital, doctor's office.

Who performs test?

• Lab technician, nurse, doctor.

Risks and precautions:

• If tourniquet is applied on the arm too long (over 1 minute), it may cause an inaccurate test result. Request another sample to be collected to ensure accuracy.

Patient preparation:

• Activity - No changes necessary.
• Diet - No changes necessary.
• Medicines - Inform the person performing the test if you have recently taken any medications listed under Taking these drugs may affect test results. You may be asked not to take this medication before the test.
• Disrobing - None required. Roll up sleeve only.

THE TEST

Sensory factors:

• Touching - You will feel mild discomfort when the needle is inserted into the vein or when the lancet pricks a finger, heel or ear lobe.
• Seeing - You will see the technician, nurse or doctor, the basket or tray to hold the equipment, the needles, syringes, collecting tubes and bandages.
• Feeling - Some degree of apprehension or fear is normal and should be expected. Discomfort disappears when the test is finished.
• Other senses (taste, smell, hearing) - Not affected.

Equipment used:

• Needles, syringes and heparinized collecting tubes. Sterile, disposable equipment prevents contamination or spread of infection. There is no risk of becoming infected with the hepatitis virus, AIDS virus or any other infecting germ.
• Stopwatch.
• Water bath set at 98.6F (37C) to place blood specimen in.

Description of test:

• Technician, doctor or nurse applies a tourniquet or blood-pressure cuff to the upper arm if blood is collected from a vein.
• Skin over the vein to be stuck is cleaned with alcohol or other antiseptic on a piece of cotton.
• When blood is drawn from a vein, the operator feels the vein to be used then punctures both the skin and vein in one quick stroke. The needle used is a sterile, disposable needle attached to a sterile, disposable syringe. (Lee-White Coagulation Time; Coagulation Time; Venous Clotting Time)
• Operator withdraws the needle and transfers sample from the collecting syringe into sterile tubes (identified with your name) before sending samples to the laboratory for analysis.
• Tubes are placed in a water bath to keep them at an even temperature.

AFTER THE TEST

Immediate post-test care:

• Apply pressure to the puncture site with cotton provided by the laboratory.
• If a vein has been punctured, raise your entire arm over your head while applying pressure.
• Some discoloration, soreness or swelling may develop at the venepuncture site. This responds well to moist, warm compresses applied every 2 to 4 hours.

Activity after test:

• Resume taking any medications that were withheld before the test.
• Return to pretest activities right away.
• Use warm compresses if blood collects under the puncture site or if the area becomes tender, red or painful.

Time before test results available:
It takes several hours to do the test. Results may not be available until the following day.

TEST RESULTS

Test values:

• Test results are determined by timing how long it takes for a collected sample of whole blood to clot.

Normal values:

• Whole-blood clotting time ranges from 5 to 15 minutes.
• After 1 hour, the clot becomes firm and retracted from the side of the test tube. Approximately 50% retraction is normal.

What ABNORMAL may indicate:

• Anemia.
• DIC.
• Hyperfibrinogenemia.
• Secondary fibrinolysis.

What HIGH or PROLONGED may indicate:

• Severe deficiency of coagulation factors.
• Presence of anti-coagulants.

What SLOW or incomplete retraction may indicate:

• Thrombocytopenia.
• Thrombasthenia.

Taking these drugs may affect test results:

• Anti-coagulants.
• Corticosteroids.
• Epinephrine.
• Tetracyclines.

Other factors that may affect test results:

• None expected.

From the Complete Guide to Medical Tests by H. Winter Griffith, M.D. © 1988 by Fisher Books; electronic rights by Medical Data Exchange.