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Activated Partial Thromboplastin Time (APTT)
Activated Partial Thromboplastin Time (APTT)
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Activated Partial Thromboplastin Time (APTT)
Category: Hemostasis.
Subcategory: Coagulation tests.
Material studied: Blood.
Estimated cost of test: $18.50.
Patient time for test: 5-10 minutes.
Reliability of test results: Good.
Available as home self-test? No.
Note: APTT is valuable in preoperative screening for bleeding tendencies.
BEFORE THE TEST
Purpose of test:
Monitors effectiveness of heparin therapy*.
Screens for deficiencies of the clotting factors in intrinsic pathways, except Factor VII* and Factor XIII*.
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--If you are receiving heparin therapy*, this test may need to be repeated at regular intervals to evaluate your response to treatment.
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 (hearing, smell, taste)--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.
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.
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 treated with an anti-coagulant chemical to prevent clotting.
If blood is collected from a finger, heel or ear lobe, skin over the selected site is cleaned with an antiseptic. The operator quickly pierces the skin to a shallow depth, using a sterile, disposable metal lancet. The drop or two of blood produced is collected into a capillary pipette.
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:
Test requires only a few minutes in the laboratory. Time before results are reported to the doctor or patient varies from a few minutes to a few days.
TEST RESULTS
Test values:
Test results are determined by timing how long it takes for a fibrin clot to form.
Normal values:
Fibrin clot forms 25 to 36 seconds after adding emulsion to blood sample.
What HIGH or TOO LONG may indicate:
Circulating anti-coagulants, such as heparin.
Fibrinolysis.
Presence of fibrin split products.
Taking these drugs may affect test results:
Heparin.
Other factors that may affect test results:
None expected.
*See Glossary.
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From Complete Guide to Medical Tests by H. Winter Griffith, M.D. Copyright by Fisher Books. Electronic rights by Medical Data Exchange.
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