science

Multiple electrode aggregometry

Multiple electrode aggregometry is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Multiple electrode aggregometry rather than just read about it. In short: Multiplate multiple electrode aggregometry (MEA) is a test of platelet function in whole blood. The test can be used to assess platelet function, monitor antiplatelet therapy, and is also investigated as a potential predictor of transfusion requirements and bleeding risk in cardiac surgery.

Key takeaways

Multiple electrode aggregometry belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Multiple electrode aggregometry to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Multiple electrode aggregometry from memory before moving on to harder problems.

Reference excerpt

Multiplate multiple electrode aggregometry (MEA) is a test of platelet function in whole blood. The test can be used to assess platelet function, monitor antiplatelet therapy, and is also investigated as a potential predictor of transfusion requirements and bleeding risk in cardiac surgery.

Instrument The Multiplate MEA Analyzer (Roche Diagnostics International Ltd) has 5 channels for simultaneous measurement of several samples or agonists. The instrument detects change in electrical impedance when platelets aggregate on metal electrodes in the test cuvette. Each cuvette contains two pairs of sensor electrodes, each of which measures the change in impedance. The duplicate sensors serve as an integrated quality control, and the analysis is accepted if the correlation coefficient of the measurements is greater than 0.98. The difference of each curve from the mean curve is also calculated, and a difference of less than 20% is accepted. The test cuvettes also contain a teflon coated magnetic stirring bar. The increase in impedance as aggregation occurs is transformed into aggregation units (AU) and plotted against time on the computer screen.

Sample The manufacturer recommends the use of hirudin as anticoagulant for samples to be tested, but studies have shown that heparin is a good alternative. 300 μL of blood is needed for each analysis, and is diluted with the same amount of saline. After pipetting blood and saline into the cuvette, the test is incubated for three minutes before the chosen agonist is added. The test is then started, and platelet aggregation is recorded at approximately 0.5 second intervals for six minutes. Three parameters are calculated: aggregation, velocity and area under the curve (AUC). Aggregation (in AU) is the maximum height of the aggregation curve, and velocity (in AU/min) is the maximum slope of the curve. AUC is the most important parameter. It is recorded in Units (U), and is affected by both the height and the slope of the aggregation curve, and is the best overall measure of platelet activity.

Multiplate Tests/Reagents

ADPtest Adenosine diphosphate (ADP) is a platelet agonist. When it is added to saline-diluted whole blood in the test cuvette, it stimulates the ADP receptors on platelets, activating the platelets. The activation of the platelets leads to shape change and degranulation, and the released content of the granules further activates the platelets. Activation also induces a conformational change in the glycoprotein IIb/IIIa (GPIIb/IIIa) receptor, giving it high affinity for fibrinogen. Binding of fibrinogen to GPIIb/IIIa receptors leads to platelet-to-platelet bridges and results in platelet aggregation. Antiplatelet drugs like clopidogrel and prasugrel irreversibly inhibit the ADP receptor P2Y12, leading to a decreased ADP-induced platelet aggregation. Drugs that inhibit the GPIIb/IIIa receptor, e.g. eptifibatide, can also reduce or eliminate the ADP-induced platelet response.

ASPItest In the ASPItest arachidonic acid is added to the saline-diluted blood sample. Arachidonic acid is converted to prostaglandin H2 (PGH2) by cyclooxygenase-1 (COX1), and PGH2 is then converted to thromboxane A2 (TXA2) by thromboxane synthase. TXA2 increases platelet aggregation, promotes degranulation and stimulates platelet activation. Inhibition of COX1, as with acetylsalicylic acid, and inhibition or absence of GPIIb/IIIa receptor, as seen in Glanzmann's thrombasthenia, will reduce platelet aggregation in response to arachidonic acid.

COLtest Collagen is added to the sample-saline mix, and binds to collagen-receptors on platelets. This leads to a release of arachidonic acid, which is converted to the potent platelet activator TXA2. COLtest is sensitive to inhibition of COX1 and GPIIb/IIIa and to Glanzmann's thrombasthenia.

RISTOtest Ristocetin forms complexes with von Willebrand factor (vWF) that bind to the glycoprotein Ib (GP1b) receptors on platelets, causing platelet activation and aggregation. Reduced or absent aggregation in response to ristocetin can be caused by a lack of or reduction of vWF, as seen in von Willebrand disease (vWD), or absence or reduction in numbers of GP1b receptors, as in Bernard–Soulier syndrome (BSS). RISTOtest can be performed in two concentrations; RISTOhigh and RISTOlow. In RISTOhigh, a ristocetin concentration of 0,77 mg/mL is applied. This normally induces a strong platelet aggregation, and low or absent aggregation can be caused by the earlier mentioned conditions vWD and BSS. In RISTOlow, the ristocetin concentration is just 0,2 mg/mL, and at a level that does not normally induce a strong aggregation response. This test can detect if vWF shows a stronger than normal tendency to aggregate platelets, which can be seen in a subtype of vWD called vWDIIb.

TRAPtest Thrombin receptor activating peptide-6 (TRAP-6) activates platelets through the thrombin receptor protease activated receptor-1 (PAR-1). Binding of TRAP-6 to PAR-1 causes a conformational change in the GPIIb/IIIa receptors on platelets, giving them high affinity for fibrinogen. Fibrinogen then binds to the receptors, crosslinking several platelets and causing aggregation. Aggregation in TRAPtest may be reduced or absent in Glanzmann's thrombasthenia, where GPIIb/IIIa receptors are few or absent, or if the patient is taking a GPIIb/IIIa antagonist. Traptest has only minor sensitivity for inhibition of COX1 and ADP-receptors.

ASA Reagent Adding ASA (acetylsalicylic acid) reagent to a blood sample reduces the aggregation responses in ASPItest and COLtest. ASA irreversibly inhibits COX1 in platelets, thereby inhibiting the production of TXA2. The ASA Reagent is used as a quality control in the platelet function testing with Multiplate, allowing the assessment of abnormal platelet responses in ASPItest and COLtest.

GPIIb/IIIa Antagonist Reagent This reagent is used as a quality control in Multiplate platelet function testing. The GPIIb/IIIa antagonist blocks the binding of fibrinogen to the GPIIb/IIIa receptors, preventing the formation of platelet-fibrinogen bonds and resulting in significantly reduced platelet aggregation in response to all agonists. The antagonist reagent is used together with TRAP-test, and allows assessment of a positive control.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Multiple electrode aggregometry

Start with the simplest possible case. Write down what Multiple electrode aggregometry claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Multiple electrode aggregometry before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Multiple electrode aggregometry ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Multiple electrode aggregometry

In research: Multiple electrode aggregometry appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Multiple electrode aggregometry in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Multiple electrode aggregometry is common in secondary-school and first-year university syllabi. It links to neighbouring topics Medical testing equipment, Medical tests, so understanding it makes those chapters shorter.
In everyday life: Look for Multiple electrode aggregometry outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Multiple electrode aggregometry in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Multiple electrode aggregometry means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Multiple electrode aggregometry out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Multiple electrode aggregometry in simple terms?

Why does Multiple electrode aggregometry matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Multiple electrode aggregometry?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Multiple electrode aggregometry.