Skip navigation | ||
|
||
Medical Encyclopedia |
|
Other encyclopedia topics: | A-Ag Ah-Ap Aq-Az B-Bk Bl-Bz C-Cg Ch-Co Cp-Cz D-Di Dj-Dz E-Ep Eq-Ez F G H-Hf Hg-Hz I-In Io-Iz J K L-Ln Lo-Lz M-Mf Mg-Mz N O P-Pl Pm-Pz Q R S-Sh Si-Sp Sq-Sz T-Tn To-Tz U V W X Y Z 0-9 |
Contents of this page: | |
Definition
This is a test of the ability of platelets, a component of blood, to clump together and cause blood clotting.How the test is performed
Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to swell with blood.
A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
The platelet aggregation test measures the rate and degree to which dispersed platelets in a sample of plasma (the liquid portion of blood) form clumps after the addition of a material that normally stimulates aggregation. These materials may include ADP (adenosine diphosphate), epinephrine, arachidonic acid, collagen, or ristocetin.
Clumping of platelets causes the sample to be more clear (less turbid). A machine measures the changes in turbidity (cloudiness) and prints a graphic recording of the results.
How to prepare for the test
The list of medications that may affect test results is increasing rapidly; notify your health care provider of any medications (including over-the-counter preparations) that you have taken within the preceding 2 weeks.How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.Why the test is performed
This test is most often indicated when there is a bleeding tendency qualitatively similar to low-platelet bleeding despite normal platelet count (normal number of platelets).Normal Values
The normal time it takes to cause clumping is temperature dependent and may vary from laboratory to laboratory. The shape of the vial is also important.What abnormal results mean
Congenital disorders that cause decreased platelet aggregation:What the risks are
Special considerations
Medications that may alter test results include:
Home | Health Topics | Drug Information | Encyclopedia | Dictionary | News | Directories | Other Resources | |
Copyright | Privacy | Accessibility | Selection Guidelines U.S. National Library of Medicine, 8600 Rockville Pike, Bethesda, MD 20894 National Institutes of Health | Department of Health & Human Services |
Page last updated: 28 October 2004 |