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Platelet Aggregation, Arachidonic Acid (Impedance)

Complete Blood Count

AA-IPAArachidonic acid-induced platelet aggregation (impedance)

Review status

Currently under review

Pending specialist review and validation.

What it shows

This test evaluates how well your platelets clump together when exposed to arachidonic acid, using an electrical method called impedance aggregometry. As platelets activate and stick to each other, the electrical resistance in the sample changes, and that change is measured.

It is commonly used as part of a broader platelet function study. Because arachidonic acid triggers the same pathway targeted by aspirin, the test is particularly useful to check for expected aspirin effect or to investigate certain platelet function problems.

Why it matters

Results help your clinician understand whether your platelets are responding normally through the arachidonic acid pathway, whether a medication like aspirin is working as intended, or whether there may be a platelet function disorder. It can be ordered when there is unexplained easy bruising, nosebleeds, heavy menstrual bleeding, or before procedures where bleeding risk needs to be assessed.

It can also help evaluate unexpected bleeding while on antiplatelet therapy or confirm recovery of platelet function after stopping medicines that affect platelets. Decisions about stopping or continuing antiplatelet drugs are made by your clinician based on your overall health, reason for treatment, and the full set of test results.

Understanding your results

Your report reflects how strongly your platelets aggregated in response to arachidonic acid. Lower-than-expected aggregation often indicates an aspirin effect or a problem in this platelet activation pathway. Higher or normal aggregation suggests little inhibition through this pathway. Interpreting this test is done alongside other platelet agonist tests, your medication list, and your clinical history.

If results do not match your symptoms or treatment plan, your clinician may review medications and supplements, repeat testing after avoiding interfering agents as advised, or order additional platelet studies. Abnormal results do not automatically mean you will bleed during procedures; they guide careful planning and should be discussed with your healthcare team.

Reference ranges

517 ohm
All sexes
0 days – 150 years

Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.

Factors that could impact Platelet Aggregation, Arachidonic Acid (Impedance)

  • Aspirin and antiplatelet drugs

    Aspirin directly targets the arachidonic acid pathway and can markedly reduce aggregation. Other agents like NSAIDs, P2Y12 inhibitors, and COX-2 inhibitors may also influence results. Never stop these without medical advice.

  • Sample handling and timing

    Platelet function is time sensitive. Delays in testing, incorrect anticoagulant, temperature extremes, or vigorous shaking can alter platelet responses and lead to misleading results.

  • Dietary supplements and substances

    Omega-3 fatty acids, ginkgo, garlic, turmeric, and alcohol can blunt platelet aggregation in some people. Always share supplement use and recent alcohol intake with your clinician.

  • Platelet count and blood characteristics

    Very low platelet counts, high or low hematocrit, and certain anemias can affect impedance measurements. Your provider will interpret results in the context of your complete blood count.

  • Acute illness and inflammation

    Infections, recent surgery, and inflammatory conditions can temporarily change platelet function. Testing during acute illness may not reflect your usual baseline.

  • Pregnancy and hormonal factors

    Physiologic changes in pregnancy and use of hormonal therapies can influence platelet function. Tell your clinician if you are pregnant or using hormonal medications.

2026

References

  1. McGill University Health Centre. (2017, May 31). Platelet Agg Arachidonic 5uM/Impedance (Task CD 1091048). Laboratory reference ranges.
  2. Clinical and Laboratory Standards Institute. (2019). Platelet function testing by aggregometry; Approved guideline (2nd ed., CLSI document H58).
  3. Mumford, A. D., Ackroyd, S., Alikhan, R., Bowles, L., Chowdary, P., Grainger, J. D., Perry, D., & Laffan, M. (2013). Guideline for the laboratory investigation of heritable disorders of platelet function. British Journal of Haematology, 162(5), 584–595.