Platelet aggregation with ADP (4 concentrations with adenosine diphosphate) (venous blood) in Moscow

Increased aggregation is a marker of hyperaggregation syndrome and thrombophilia. The most commonly used are the Born turbidimetric method, based on recording changes in the light transmission of platelet-rich plasma, and the method for studying platelet aggregation, based on the analysis of light transmission fluctuations caused by a random change in the number of particles in the optical channel.

Material for research.

Citrate platelet rich plasma

Research method

is determined by the operating procedure on a particular type of aggregometer.

Solutions of ADP, ristocetin, collagen, adrenaline, and arachidonic acid are most often used as inducers. Solutions of thrombin, serotonin, etc. can also be used.

When should you take the Platelet Aggregation with ADP test (4 concentrations with adenosine diphosphate)?

• Before prescribing drugs that affect the coagulation system.
• Differential diagnosis of diseases accompanied by pathological bleeding.
• As part of a comprehensive assessment of the platelet component of hemostasis in patients before (major) surgery, as well as in pregnant women at high risk of developing obstetric complications.
• Determination of resistance to drugs from the group of antiplatelet agents.
• Identification of hereditary and acquired thrombocytopathies.

Reasons for decreasing and increasing aggregation

Increased aggregation level or hyperaggregation is a condition in which blood flows slowly through the vessels and quickly clots. Provocateurs of such deviation can be:

• diabetes;
• hypertonic disease;
• cancer of the kidneys, gastrointestinal tract or blood;
• vascular atherosclerosis;
• leukemia;
• sepsis;
• lymphogranulomatosis;
• surgical excision of the spleen;
• menstruation in women.

Moderate platelet hyperaggregation during pregnancy is normal. This deviation occurs due to the need to nourish the placenta with blood. The value reaches its peak in the 3rd trimester of gestation.

A decrease in platelet aggregation occurs due to the following pathologies:

• thrombocytopathy;
• diseases of the hematopoietic system;
• use of antiplatelet agents;
• renal failure;
• dysfunction of the thyroid gland;
• anemia;
• alcohol abuse.

Platelet aggregation

References

1. Clinical laboratory diagnostics, National guidelines, Volume 1, Dolgov V.V., Menshikov V.V., 2012, pp. 761-765
2. Kozlovsky V. I., Kovtun O. M., Seroukhova O. P., Detkovskaya I. N., Kozlovsky I. V. Research methods and clinical significance of platelet aggregation. Focus on spontaneous aggregation // Vestnik VSMU. 2013. No. 4.
3. Puri RN, Colman RW.ADP-induced platelet activation.Crit Rev BiochemMol Biol. 1997;32(6):437-502. doi: 10.3109/10409239709082000. PMID: 9444477.
4. Murugappa S, Kunapuli SP. The role of ADP receptors in platelet function.FrontBiosci. 2006 May 1;11:1977-86. doi:10.2741/1939. PMID: 16368572.
5. Barbara Lunghi, Anna Lecchi, Rosa Santacroce, Mariangela Scavone, Rita Paniccia, Andrea Artoni, Christian Gachet, Giancarlo Castaman, Maurizio Margaglione, Francesco Bernardi, Marco Cattaneo. Severe bleeding and absent ADP-induced platelet aggregation associated with inherited combined CalDAG-GEFI and P2Y12 deficiencies.Haematologica 2020;105(7):e361-e364

Indications for analysis

Platelet aggregation is studied when:

• hemorrhagic disorders (increased bleeding);
• thrombophilia (coagulation disorder with an increased risk of thrombosis);
• severe atherosclerosis;
• diabetes mellitus;
• before performing surgical interventions;
• during pregnancy;
• when monitoring the effectiveness of anticoagulant and antiplatelet therapy.

Also, this study is important in the diagnosis of hereditary hemorrhagic thrombocytopathies.

Increased and decreased platelets in the blood

We continue our series of publications about laboratory blood tests. On our portal you can find useful information on how to independently decipher indicators in general and biochemical analyses, as well as in the lipid profile. This time Dr. Fedorov answers questions about platelet levels in the blood:

• What does a decrease in platelet levels in the blood indicate?
• What does an increase in platelet levels in the blood indicate?
• How does a blood clot form? Why is a test for induced platelet aggregation prescribed?
• Why is it important to order a blood test for platelet resistance to aspirin and clopidogrel?

The ability of blood to clot is one of the foundations of life. After all, if this mechanism had not been laid down, any, even the most insignificant wound, would become mortally dangerous. A number of biochemical compounds, which are usually called factors, are responsible for the coagulation system, but the basis of the process is the smallest formed elements of blood - platelets. Unfortunately, disruption of this system can lead to consequences no less serious than bleeding.

An excess of platelets threatens to increase the risk of intravascular thrombus formation; low platelets in the blood are the cause of internal hemorrhages.

What does a decrease in platelet levels in the blood indicate?

The lower limit of normal blood platelet content is 150 thousand/μl. The reason for the decrease in PLT (platelet designation in a blood test) may be numerous but rare congenital thrombocytopenias (Fanconi syndrome, Wiskott-Aldrich, etc.), as well as acquired thrombocytopenias. The most common cause of acquired ones is the constant use of antiplatelet drugs, especially with two-component therapy (acetylsalicylic acid + clopidogrel); fortunately, the number of platelets in this case is usually not greatly reduced. Other causes of low blood platelets include bacterial and viral infections, anemia, splenomegaly, congestive heart failure, etc.

Clinical signs of platelet deficiency (bleeding gums, bruising, frequent hemorrhages in the sclera, etc.) appear when the platelet level drops below 50 thousand/µl - this is the indicator when you need to see a hematologist immediately.

What does an increase in platelet levels in the blood indicate?

The upper limit of normal platelets in a blood test is 400 thousand/µl. Increased platelet levels are much more likely to occur for physiological reasons. These are so-called reactive thrombocytosis. Their cause may be recent physical overexertion, past stress, dehydration, that is, physiological thickening of the blood. Pathological factors most often include those that also thicken the blood - anemia due to chronic blood loss or acute blood loss, dehydration as a result of intoxication. The reasons for an absolute increase in platelet levels include inflammatory diseases, tuberculosis, malignant neoplasms in general and the hematopoietic system in particular.

An increase in platelet levels above 500 thousand/µl significantly increases the risk of thrombosis and requires the selection of antiplatelet therapy - the use of special drugs.

How does a blood clot form? Why is a test for induced platelet aggregation prescribed?

Normally, platelets in the blood are in an inactive state; the cells have a discoid, slightly elongated shape, which is why in old textbooks they are called “blood plates.” When bleeding begins, platelets are activated: they acquire a spherical shape and form special outgrowths - pseudopodia. With their help, they can connect with each other (aggregate) and stick to the site of damage to the vascular wall (adhere). These two processes provide the basis for thrombus formation.

To assess the quality of platelet aggregation and find out whether it is reduced or, conversely, does not occur too intensely, an analysis for induced platelet aggregation is prescribed. To do this, they take blood from a vein, add special substances (activation inducers) to it and evaluate the process.

When preparing for the study, it is important to comply with certain conditions - for 3 days, follow a special diet prepared by a doctor, 24 hours before, avoid taking stimulants (coffee, alcohol, nicotine, garlic) and immunostimulant drugs, 8 hours before, stop taking medications and fatty foods.

Low platelet activity occurs in diseases of the hematopoietic system, constant use of antiplatelet drugs, in this case the duration of bleeding increases. Increased aggregation, on the contrary, increases the risk of thrombosis: venous thrombosis, heart attack, stroke. You may ask, why order an induced activation test if the risk of bleeding/thrombosis can be assessed by the total platelet count? Alas. Even with normal numbers, most of the cells may turn out to be “defective”, so we are talking about severe platelet deficiency with their normal concentration in the blood.

Why is it important to order a blood test for platelet resistance to aspirin and clopidogrel?

According to research, 35% of people have a reduced antiaggregation effect when using aspirin, and in 19% it has virtually no effect on aggregation. This means that in every fifth patient, aspirin does not help avoid complications of atherosclerosis. Less common, but no less clinically important, is resistance to clopidogrel, a drug that is vitally important to take after arterial stenting. Therefore, it is considered justified to order a test for aspirin and clopidogrel resistance before prescribing these drugs, especially when stenting of the coronary arteries is planned. To diagnose aspirin resistance, two tests are used today: optical aggregometry, which is considered the “gold standard,” as well as several types of portable test systems. A similar approach is used to diagnose resistance to clopidogrel, which, according to studies, is registered in 11% of patients receiving the drug. If resistance is detected, doctors have room for maneuver - to prescribe a drug from another group and avoid dangerous complications.

The platelet level allows you to assess both the risk of thrombosis and, conversely, the likelihood of insufficient blood clotting, which threatens the development of internal hemorrhages and bleeding. Studying platelet function gives the doctor the opportunity to correctly select antiplatelet therapy - an essential component of the prevention and treatment of cardiovascular diseases.

If you still have questions, you can ask them using the Doctis service.

Classification

Clinicians distinguish several types of the described process:

• spontaneous platelet aggregation - detected without the use of an inducer substance: venous blood in a test tube is placed in a special apparatus (platelet aggregation analyzer) and heated to 37 degrees;
• induced platelet aggregation - carried out using inducers;
• low AT - diagnosed when pathologies of the circulatory system occur;
• increased AT is fraught with an increased risk of thrombosis;
• moderate AT - such platelet aggregation is often observed during pregnancy, which is caused by placental blood circulation.

Features in children

Despite the fact that increased aggregation capacity is usually found in the adult population, recently there has been an increase in cases of the disease in children.

Hyperaggregation can be either hereditary or acquired. The causes of elevated platelet levels are not much different in adults. Mainly:

• diseases of the circulatory system;
• infectious and viral diseases;
• surgical intervention.

1. In children under one year of age, hyperaggregation can be caused by dehydration and anemia. In adolescence, stressful situations and physiological growth of the body play an important role.
2. Hypoaggregation in children manifests itself in the form of nosebleeds and bruises. Girls in adolescence may experience heavy periods. In 100% of cases, pinpoint rashes are observed on the skin, and 20% of children experience bleeding gums.

Treatment begins with finding out the cause of the deviation from the norm in platelet aggregation ability. Sometimes adjusting your diet and drinking regime is enough. In some cases, treatment of the disease that caused the abnormality is required.

Platelets in child tests:

If necessary, a hematologist will conduct an additional examination and prescribe medication according to the patient’s age and severity of the disease.

Normal indicators

The aggregation rate is individual. In a healthy adult, a concentration of 25 to 75% is considered acceptable. This analysis result indicates the absence of oxygen starvation and good blood clotting.

The increase or decrease in the indicator is dictated by the platelet count, which depends on the influence of several factors (age and gender). Acceptable platelet parameters include:

The platelet level affects the process of blood aggregation or sticking together. In a healthy body, the function is protective - blood clots form, clog the wound and stop bleeding. In some cases, the occurrence of blood clots is extremely undesirable, since they block the blood vessels of vital organs, which can be fatal.

For example, high activity of colorless blood cells in most situations leads to pulmonary embolism, heart attacks and strokes. Decreased platelet production can cause massive blood loss. Frequent and long-term bleeding is complicated by exhaustion and anemia.

Carrying out analysis and deciphering it

The study of platelet aggregation makes it possible to detect deviations from the norm and diagnose pathologies of the cardiovascular or hematopoietic systems. The procedure is necessary to monitor the dynamics of the course of certain diseases and control the treatment.

After collecting the biological material, special substances are added to the blood - inducers, which are similar in structure to the cells of the body that promote thrombus formation.

The inductor can be:

• adenosine diphosphate or ADP - platelet aggregation with ADP is considered the most common test method;
• adrenalin;
• ristomycin;
• arachidonic acid;
• collagen;
• serotonin.

The method for establishing aggregation is based on the passage of light waves through the blood plasma both before and after clotting. The following properties of the light wave are taken into account:

• What does it mean that platelet aggregation with ADF is reduced in the analysis?

• character;
• form;
• speed.

All this happens in a machine called a platelet aggregation analyzer. The equipment is available in every Helix laboratory service.

The analysis is deciphered by a hematologist, and the indicator depends on the substance that was added to the test liquid and its concentration.