From the Guidelines
Platelet function tests, including light transmission aggregometry, flow cytometry, and thromboelastography, are the primary lab tests that show platelet dysfunction. These tests are essential for diagnosing conditions like von Willebrand disease, Glanzmann thrombasthenia, Bernard-Soulier syndrome, and medication-induced platelet dysfunction from drugs like aspirin or clopidogrel 1.
Key Tests
- Light transmission aggregometry (LTA) measures how well platelets clump together in response to various agonists like ADP, collagen, and epinephrine
- Flow cytometry assesses platelet surface receptors and activation markers, including GPIIb/IIIa, GPIIIa, GPIb, and GPIb/IX
- Thromboelastography (TEG) or rotational thromboelastometry (ROTEM) evaluate the entire clotting process including platelet contribution
Diagnostic Approach
The diagnostic work-up for inherited platelet function disorders (IPFD) typically involves a combination of first-step and second-step tests 1. First-step tests include LTA, flow cytometry, and assessment of platelet granule release. Second-step tests may include additional LTA with an expanded agonist panel, flow cytometry with additional antibodies, clot retraction, and transmission electron microscopy (TEM) 1.
Test Interpretation
Impaired platelet aggregation with one or more agonists is suggestive of some IPFD, while defective granule release may indicate disorders such as grey platelet syndrome or Quebec platelet disorder 1. Flow cytometry can help identify specific platelet surface glycoprotein defects, such as those seen in Glanzmann thrombasthenia or Bernard-Soulier syndrome 1.
From the Research
Lab Tests for Platelet Dysfunction
The following lab tests can be used to show platelet dysfunction:
- Platelet Function Analyzer (PFA)-100 test, which measures the ability of platelets to occlude an aperture in a membrane treated with collagen and epinephrine (CEPI) or collagen and ADP (CADP) 2
- Light transmission platelet aggregometry (LTA) analyses, which can detect abnormalities associated with increased bleeding in a significant proportion of individuals referred for platelet function disorder investigations 3, 4
- Quantitative analysis of platelet dense granule numbers, which can detect abnormalities associated with increased bleeding in a significant proportion of individuals referred for platelet function disorder investigations 4
- Lumiaggregometry estimates of platelet adenosine triphosphate release, although this test has greater variability and limited diagnostic usefulness 4
- Whole blood platelet aggregation studies, which can be used to support the results of other tests, such as the PFA-100 test 2
- Electron microscopy (EM), which is the best method for diagnosing platelet delta granule storage pool deficiency (δ-SPD) 3
Limitations of Lab Tests
The lab tests for platelet dysfunction have some limitations, including:
- The PFA-100 test may not be suitable for all patients, and the results should be interpreted with caution 2
- LTA analyses may not reliably diagnose platelet delta granule storage pool deficiency (δ-SPD) 3
- The diagnostic usefulness of lumiaggregometry estimates of platelet adenosine triphosphate release is limited due to greater variability 4
- The availability of lab tests for platelet dysfunction may be limited by fiscal and other constraints, including a lack of high-quality evidence 4