Platelet count can be performed manually with a hemocytometer or utilizing an automated analyzer. Platelet numbers can also be estimated by a laboratory examination of your blood via a blood smear.
Many laboratories have instruments that count platelets effectively, along with leukocytes and red cells. Because of this, platelet count can be reported routinely on automated or complete hemograms.
Platelet numbers are an essential reading on the hemogram and are vital for diagnosing a bleeding patient.
What are Platelets?
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Thrombocytes, also known as platelets, are small cell elements that are formed within the body’s bone marrow. These elements are actually tiny megakaryocyte cytoplasm fragments (platelet cell precursor).
The release of these fragments, known as platelets, into the bloodstream aids in controlling both internal and external bleeding.
Platelets accomplish this via two means. The first is by the formation of an occlusion at the injurious blood vessel opening. The second is the thromboplastic function that works to stimulate a coagulation cascade.
Both platelet function and platelet numbers in the body play a crucial role in platelet’s ability to control bleeding within the body.
Note that when you estimate a platelet count, you are only measuring the number and not the effectiveness of platelet function.
In the case when a patient has a decreased platelet count, severe internal bleeding can occur. This can be caused by a variety of conditions such as:
- Leukemia, which causes malignant cells to replace bone marrow
- Drug-induced medication
- Aplastic anemia, where the patient has experienced a loss in healthy functioning of bone marrow
Other conditions can reduce the overall function of platelets.
Platelet count can be elevated through the following conditions:
- Chronic inflammation or infection. Disease stage and therapeutic regimen should be kept in mind; both of which can cause platelet numbers to fluctuate
- Iron deficiency anemia
- Chronic leukemia, dependent on therapy and disease stage
- Essential thrombocythemia
Furthermore, some other conditions can affect the overall function of platelets such as cholesterol levels, elevated lipi, smoking, diabetes, and atherosclerosis.
These conditions can enhance an individual’s chance of developing a thrombosis condition. Average platelet levels are 150,000-450,000/cubic mm.
Estimating Platelet Count
Platelet count can be estimated from a well-prepared blood smear examination. Platelets can be estimated by counting the average number of platelets that are visible under a monolayer 100x oil immersion field.
In general, the analyzer will examine 10 oil immersion field and conduct an average result. This result will account for any uneven platelet dispersal within the blood smear.
The following formula will then be applied:
Estimated platelet count/uL = the count average in 10 fields x 15,000
For example, if the average observable field contains 7 platelets, estimations of 105,000/uL would be appropriate. This value is then compared to normal levels in the human body (150,000 – 450,000). In this scenario, this value of 105,000 would be considered low, but not necessarily at risk for internal bleeding.
Manual Platelet Count
Platelet count can be performed manually under a microscope utilizing a commercial diluting system known as a hemocytometer. These counts are not as accurate as automated platelet counts are. This is because platelets are difficult to distinguish from debris. In a hemocytometer count, platelet clumping will also decrease observable levels.
Automated Platelet Count
Automated platelet count can be measured based on light-scattering principles by flow of cytometry. This can also be identified by their size, refractive index (high angle light scatter n=1.40 to n=1.35) and low angle light scatter (<30 FL).
All blood smear is reviewed for the presence of platelet clumps. The presence of platelet clumps can affect the accuracy of platelet count. Platelet count obtained via any method will decrease if there are platelet clumps. Therefore, any platelet count that has been determined should be considered the absolute minimum of a given sample. However, if a sample has severe platelet clumps, it should be discarded completely.
Under circumstances such as these, along with any other erroneous accounts, including iron deficient camelid, platelet count cannot be provided and a platelet blood smear estimate should be used as an actual guide.
Clumping of platelets can be caused by a variety of reasons including a problem during sample collection. This result can be minimized by collecting blood from a jugular or cephalic (large peripheral) vein. This will aid in the smooth flow of blood into the syringe or vacutainer.
Following collection, the blood sample should be mixed with anticoagulant by gentle inversion or rotation. Platelet clumping is known to increase with time, so counts should be performed as soon as possible following the collection in order to maintain the highest levels of accuracy.
Platelet Test Interpretation
Thrombocytopenia – Decreased Platelet Number
Causes of low platelet count can fall into one or a combination of these general mechanisms:
- Loss with acute severe hemorrhage
- Sequestration of platelets in microvasculature or spleen
- Increased clearance/destruction of platelet by macrophages
- Increased platelet consumption in coagulation
- Decreased platelet production in the bone marrow
- Iatrogenic: Hemodilution
- Artifact of collection (clumping)
Thrombocytosis – Elevated Platelet Number
Thrombocytosis can occur either through primary myeloproliferative types of conditions or as a reactive (secondary) phenomenon in a variety of pathologic and physiologic states.
This condition is generally caused by a heightened platelet production and release into the bloodstream. In cases that are reactive, this effect is likely due to an increase in thrombogenic cytokines such as thrombopeiotin interleukin-6, rather than platelets that have an increased lifespan.
Typically, the platelet count that is higher than the interval referenced within the human body is secondary thrombocytosis and is not always of direct importance pathologically.