Platelets & Investigations

Platelets
Fragments of megakaryocyte cytoplasm

Megakaryocytes
- giant cells
- multilobulated nuclei
- fr red bone marrow

Platelet Structure
Discus with surface openings on the membrane that connect to the canalicular system
Contains 2 granules
- dense (rich in ADP)
- alpha (contain fibrinogen/factor V, vWF & PA1-1)
and lysosomes
Cytoplasm = Coag Fx - a/w/ the surf membranes

Normal function
BV damage
Plts attach to exposed collagen (underneath endothelial vessel lining)
Plts shape change & degranulate
= ADP release
= activates nearby Plts
Phospholipid released from plts = coagulation system

Defects - can be in no. or function

Tests
Test of number
Electronic particle counters
Blood film

Function test
Bleeding time
 - cuff and cut
Norm <10minutes
New: In-vitro BTs

or

Lab aggregating agents (ADP/collagen) + light transmittance through plasma

Two Basic Initial Tests
1) Plt Count (n = 150-400)
NB if init. low - *artefactual, clot in sample therefore repeat
2) Bleeding Time (n = 2-10 minutes)