Overview
Platelet function tests evaluate how platelets respond to agonists (e.g., ADP, collagen, arachidonic acid, ristocetin) or how they occlude apertures under shear.
Clinical Importance
To evaluate unexplained mucocutaneous bleeding with normal platelet count
To investigate inherited or acquired platelet function disorders and selected drug effects
Specimen Requirements
- Citrate whole blood or platelet-rich plasma depending on method
- Atraumatic draw; short tourniquet time; test within method stability (often same day)
- Patients should avoid interfering medications when clinically safe and protocol requires
Analytical Method
Light-transmission aggregometry measures increased light transmission as platelet-rich plasma aggregates after agonist addition.
Cartridge/shear-based systems measure closure time under high shear with collagen/epinephrine or collagen/ADP membranes.
Instruments Used
Automated analyzers
- Cartridge-based platelet function analyzers (PFA-class systems)
- Automated aggregometers on specialized hemostasis benches
Manual methods
- Classic light-transmission aggregometry with multiple agonists
Reference Values
Typical adult SI examples below follow widely published international hematology practice (e.g., Dacie and Lewis; Henry's). Always interpret against the method- and demographics-specific interval printed on the patient report (CLSI EP28-A3c). Neonatal, pediatric, pregnancy, and altitude intervals differ.
Agonist- and method-specific. Closure times and aggregation percentages use laboratory-validated intervals.
Interpretation
Common Causes of Increased Results
- Prolonged closure times or reduced aggregation responses suggest platelet dysfunction, VWD patterns (selected agonists), or drug effect
Common Causes of Decreased Results
- Hyperaggregation patterns are less commonly used clinically and require specialist interpretation
Clinical Significance
- Bleeding disorder evaluation after CBC and coag screens
- Selected perioperative or antiplatelet effect assessments per protocol
Factors Affecting Results
Pre-analytical
- NSAID/antiplatelet drug exposure
- Low hematocrit or low platelet count invalidating some cartridge assays
- Delayed testing or cold storage of samples
Analytical
- Agonist potency and instrument settings
Post-analytical
- Interpreting a single agonist in isolation without the panel pattern
Advantages and Limitations
Advantages
- Assesses function rather than count alone
- Aggregometry patterns help classify disorders
Limitations
- Specialized, time-sensitive testing
- Affected by drugs, hematocrit, and platelet count
Clinical Pearls
A normal platelet count never proves normal platelet function; when bleeding is mucocutaneous, test function (and vWF) deliberately.
References
Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.
Textbooks
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
- Rodak BF, Carr JH. Rodak's Hematology: Clinical Principles and Applications. 6th ed. Elsevier; 2020.
- Hoffbrand AV, Moss PAH, Pettit JE. Essential Haematology. 8th ed. Wiley-Blackwell; 2019.
- McKenzie SB, Williams JL. Clinical Laboratory Hematology. 4th ed. Pearson; 2022.
- Bain BJ, Bates I, Laffan MA. Dacie and Lewis Practical Haematology. 12th ed. Elsevier; 2017.
- Kaushansky K, et al. Williams Hematology. 10th ed. McGraw-Hill; 2021.
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays and Molecular Hemostasis Assays; Approved Guideline. CLSI document H21-A5. CLSI; 2017.
- Clinical and Laboratory Standards Institute. One-Stage Prothrombin Time (PT) Test and Partial Thromboplastin Time (PTT) Test; Approved Guideline. CLSI document H47-A2. CLSI; 2008.
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
- Clinical and Laboratory Standards Institute. Management of Critical- and Significant-Risk Results. CLSI guideline GP47-Ed1. CLSI; 2015.
Frequently Asked Questions
Common questions about using this Platelet Function Testing laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Platelet Function Testing laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of Platelet Function Testing. Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find Platelet Function Testing specimen requirements?
See the Specimen Requirements section on this page for specimen information related to Platelet Function Testing. Confirm collection details against your laboratory protocol.
Where are Platelet Function Testing reference values listed?
See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.
How do I interpret Platelet Function Testing results?
Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.
What analytical method is used for Platelet Function Testing?
See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.
Are related laboratory tests linked from Platelet Function Testing?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading Platelet Function Testing?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Hematology topic.
What are the clinical pearls for Platelet Function Testing?
See the Clinical Pearls section for concise laboratory practice notes associated with Platelet Function Testing. Apply pearls alongside institutional protocols.
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