Platelet Hyperaggregation [CO004000]
Related Information
Synonyms Hypercoagulable State, Platelet Aggregation; Platelet
Aggregation, Hypercoagulable State; Platelet Autoaggregation
Test Includes Evaluation for spontaneous aggregation, and
aggregation in response to low concentrations of adenosine diphosphate
(ADP), epinephrine, arachidonate, and collagen
Abstract Platelet hyperaggregation in response to platelet
agonists, and/or spontaneous platelet aggregation (aggregation without
a platelet agonist) has been described in association with hypercoagulability,
including strokes, myocardial infarction, and less commonly venous
thrombosis.
Patient Preparation Patients should not have aspirin (or
any medication containing aspirin) for at least 7 days prior to
testing. Nonsteroidal anti-inflammatory drugs or other platelet-inhibiting
agents should also be avoided.
Specimen Platelet-rich plasma
Container Four to six blue top or plastic (sodium citrate)
tubes
Collection Routine venipuncture. Immediately invert tubes
gently at least 4 times to mix. Deliver tubes immediately to the
laboratory at room temperature (platelets are activated at cold
temperatures).
Storage Instructions Keep specimen at room temperature and
perform test within 2 hours of collection. Do not refrigerate or
freeze specimen.
Causes for Rejection Specimen received more than 2 hours
after collection, specimen clotted, specimen received on ice
Turnaround Time Less than 1 day
Special Instructions Test usually must be scheduled in advance
with the laboratory.
Reference Interval No spontaneous platelet aggregation and
no hyperaggregation compared to a normal control. Normal newborns
can have decreased aggregation compared to adults.1
Use Evaluation for excessive platelet aggregation may be
useful in patients with evidence of unexplained hypercoagulability
and normal values in the routine hypercoagulation test panel.
Limitations Subjective. Results are compared to a normal
control. Variable results among patients and controls. Platelet-inhibiting
medications interfere. Labor-intensive for the laboratory, therefore,
not suitable for high volume clinical testing.
Methodology As described for platelet aggregation, except
each platelet agonist is tested at multiple lower-than-usual concentrations.
For example, instead of testing epinephrine only at 10 microM, it
is tested at 10 microM, 5 microM, 1 microM, and 0.5 microM. No agonist
is added to one aliquot to assess for spontaneous aggregation.
Additional Information Various medications can cause increased
in vitro platelet aggregation. If a patient is found to have
increased platelet aggregation in this assay, a careful review of
prescribed, as well as over-the-counter medications, is indicated.
An on-line literature search for each medication is often informative.
Hyperaggregation has also been reported with myeloproliferative
disorders. Hereditary hyperaggregation as a cause of hypercoagulability
is not well characterized.
Footnotes
1. Michelson AD, "Platelet Function in the Newborn,"Semin Thromb
Hemost, 1998, 24(6):507-12.
References
Mammen EF, "Sticky Platelet Syndrome,"Semin Thromb Hemost,
1999, 25(4):361-5.
Landolfi R, Marchioli R, and Patrono C, "Mechanisms of Bleeding
and Thrombosis in Myeloproliferative Disorders,"Thromb Haemost,
1997, 78(1):617-21.
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