Platelet Count

Specimen Required

3cc EDTA BLOOD (CBC VIAL)

Fasting Required

Purpose of the Test

To count the number of platelets present in blood. This may be performed if there are symptoms of a bleeding disorder, an unexplained blood clot, or to check that the bone marrow is working as it should.

When this test is required

In general, a platelet count may be requested for the following reasons: As part of the general screening panel looking at blood cell characteristics during full blood count analysis When trying to diagnose the cause of unexpected or prolonged bleeding, or in cases of unexplained or easy bruising For investigating the cause of petechiae or purpura (small red/purple spots in the skin caused by bleeding from small blood vessels) For monitoring purposes where patients are on drugs known to affect platelet count During the investigation of suspected blood or bone marrow diseases During the investigations of an unprovoked blood clot

What the Test Detects

Platelets are small cell fragments and are found in the blood along with red cells and white cells. Platelets are produced in the bone marrow and released into the blood where they play an important role in coagulation (blood clotting), helping to stop bleeding when blood vessels are injured. They are the first cells to be recruited to sites of injury and, when activated, they clump together (aggregate), sealing the blood vessel…Platelets are small cell fragments and are found in the blood along with red cells and white cells. Platelets are produced in the bone marrow and released into the blood where they play an important role in coagulation (blood clotting), helping to stop bleeding when blood vessels are injured. They are the first cells to be recruited to sites of injury and, when activated, they clump together (aggregate), sealing the blood vessel and forming a blood clot. These small, disc-shaped cells usually live for around 5-10 days in the blood before they are destroyed. Platelets are very important for efficient blood coagulation and preventing unnecessary or excessive blood loss. If there are too few platelets, or if the platelets that are present don’t function properly, then there may be problems with blood clot formation. On the other hand, too many platelets can increase the risk of blood clots that can block blood vessels and cause organ damage. The platelet count simply provides information on the number of these cells that are present in blood; it does not reveal if these cells are functioning properly. Specialised tests, called the platelet function tests, are used when there is suspicion of a platelet function defect. How is the sample collected for testing? The platelet count is performed on a sample of blood obtained from a vein in the arm using a needle. This is a process which may be referred to as ‘venepuncture’. Is any test preparation needed to ensure the quality of the sample? No test preparation is needed. See MoreSee Less

Preparation for the Test

None

Sample Requirements

A blood sample taken from a vein in your arm

Additional Notes

Platelets are cells that have a short life-span in the blood (5-10 days), which means the count can rise and fall quickly in response to disease or trauma. Short-term increases in platelet counts are known to be associated with strenuous exercise, childbirth and extreme stress.The platelet count will be falsely reduced if there are errors in taking the blood and it is allowed to clot in the sample tube before it reaches the laboratory. However, low and high counts are investigated thoroughly in the laboratory with samples checked for clots and blood films looked at under the microscope to check the number count that is reported genuinely reflect the numbers of platelets present.Sometimes, the EDTA present in the Full Blood Count sample tube causes the platelets to stick together and so the analysers give a falsely low reading. This is why blood films are checked to see if these platelet clumps can be seen. In these situations, a Citrated Full Blood Count is performed as the citrate anticoagulant doesn’t cause this problem. This is the only way to get an accurate platelet count in this situation. Some people have a tendency to form clumps and so they always need a citrated sample. No one knows why some people are affected and not others, but there is no known association with other conditions.Living at high altitudes and drugs that include oestrogen (including oral contraceptives) can increase the platelet count. Alternately, slightly reduced platelet counts are seen in women prior to menstruation.If an abnormal platelet count is detected then the results of the other blood cells analysed in the full blood count, as well as any other tests that have been performed will be taken into consideration and further investigations (blood tests) may be requested. This information, along with any clinical signs and symptoms will be considered by your healthcare professional who will be able to provide you with more information regarding the significance of the results.

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