Platelet specific proteins include beta-thromboglobulin, platelet factor 4, platelet-derived growth factor and thrombospondin. They are contained within the platelet alpha granules but are absent in the plasma of normal individuals. The ratio of beta-thromboglobulin-to-platelet factor 4 can be used as a measure of platelet activation, with an increase in the ratio being seen during activation of platelets in vivo.
ß-thromboglobulin
platelet factor 4
normal
normal
normal
in vivo release
increased
normal or slightly increased
in vitro release
increased
increased
in vivo heparin administration
normal
markedly increased
renal failure
increased
normal
Specimen Collection: Since sample agitation or trauma can result affect release of these proteins, specimens should be treated with special care and tested promptly. If the specimen must be sent to a reference laboratory, citrated plasma should be frozen as soon as possible.
Calculation:
beta-thromboglobulin to platelet factor 4 ratio =
= (beta-thromboglobulin in ng/mL) / (platelet factor 4 in ng/mL)
Interpretation:
• a ratio of 5:1 is normal and indicates no platelet activation
• a ratio of 1:1-to-5:1 indicates in vitro activation
• a ratio of 5:1-to-10:1 is seen with in vivo activation
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