Page 516 - Clinical Hematology_ Theory _ Procedures ( PDFDrive )

500 PART 7 ■ Principles and Disorders of Hemostasis and Thrombosis

e sures the inter ction between the c pill ries n pl te- T e pl telet ggreg tion proce ure is per or e on tur-

lets. Pl telet hesiveness is the process o the sticking o bi i etric ggrego eter s f rst escribe by Born. Ch nges

pl telets to the vessel w ll, where s pl telet ggreg tion is the in ggreg tion re recor e s pl telet-rich pl s , n

sticking or clu ping o pl telets to e ch other. T e blee ing ggreg ting re gents re stirre together in cuvette. T e

ti e re ects these spects o pl telet unction. ggrego eter serves s st n r ize spectrophoto eter.

As the pl telet count rops below 100 × 10 /L, the blee - As ggreg tion procee s, ore light p sses through the
9
ing ti e incre ses progressively ro nor l o 3 to 8 in- s ple.

utes to ore th n 30 inutes. A prolonge blee ing ti e Epinephrine is usu lly use in two oses, s is ADP. A

in p tient with pl telet count gre ter th n 100 × 10 /L onoph sic curve is elicite with ADP. A biph sic curve
9
in ic tes either i p ire pl telet unction or e ect o sub- is usu lly elicite with epinephrine. Ristocetin n r -

en otheli l ctor. Results between 8 n 11 inutes re usu- chi onic ci lso usu lly in uce onoph sic curve.

lly not clinic lly signif c nt. Lu i ggreg tion is n extension o ggreg tion.

T e onset o the e ect o spirin is r pi . Pl telet inhibition For ore th n 20 ye rs, ristocetin co ctor (RCo) ss y

is e sur ble within 60 inutes. T e e ects o spirin l st or (which e sures vWF) e i te gglutin tion o pl te-

the ur tion o the li e sp n o the pl telet, pproxi tely 7 lets in the presence o the ntibiotic, ristocetin, n h s

to 10 ys. With bor erline results, the spirin toler nce test been the ost co only use ss y or the e sure ent

is o en use ul n is repe te 2 hours er spirin ch llenge. o the unction l ctivity o vWF. Recently, coll gen-

bin ing enzy e-linke i unosorbent ss y (ELISA) h s

Clot Retraction been intro uce s n ltern tive proce ure. Circul ting

T e contr ctile bilities o pl telets lso result in the con- pl s vWF ntigen is rker o gener lize en otheli l

tr ction o or e clots. Clot retr ction re ects the nu ber ys unction.

n qu lity o pl telets, f brinogen concentr tion, f brino-

lytic ctivity, n p cke re cell volu e. Bec use the f brin Platelet Adhesion

clot en eshes the cellul r ele ents o the bloo , pri rily Pl telet hesion in vivo occurs s pl telets tt ch either to

erythrocytes, the egree o clot retr ction is li ite to the ge vessel w ll or to e ch other. Metho s o in vitro

extent th t f brin contr cts by the volu e o erythrocytes n lysis rely on the herence o pl telets to gl ss sur ces.

(he tocrit). T ere ore, the s ller the he tocrit, the T e ount o herence o pl telets in bloo s ple to

gre ter the egree o clot retr ction. gl ss sur ce c n be e sure by counting the nu ber o

T e egree o clot retr ction is irectly proportion l to the pl telets be ore n er exposure to gl ss be s. T e reli-

nu ber o pl telets n inversely proportion l to the he - bility o this etho ology h s been questione ; there ore,

tocrit n the level o the bloo co gul tion ctor f brino- use o the etho is not univers l.

gen. When clot issolution (f brinolysis) is very ctive, the

f brin clot y be issolve l ost s quickly s it is or e , Antiplatelet Antibody Assays

n clot retr ction is i p ire . Antibo ies g inst pl telets y ppe r in the pl s o
p tients in cert in clinic l con itions, lthough it y be

Platelet Aggregation i cult to e onstr te these ntibo ies in c ses o i une

Most pl telet ggreg tion proce ures (see Ch pter 32) re thro bocytopeni . Av il ble techniques c n inclu e co -

b se on so e v ri tion o Born etho . Agents such s ple ent f x tion etho s, lysis o chro iu 51–l bele

ADP, coll gen, epinephrine, sn ke veno , thro bin, n pl telets, ss ys o pl telet-boun i unoglobulins, n

ristocetin c n be use to ggreg te pl telets. T e principle o co petitive inhibition ss ys.

the test is th t pl telet-rich pl s is tre te with known

ggreg ting gent. I ggreg te , clou iness or turbi ity c n NOTE: This is a good time to complete the end of chapter

be e sure using spectrophoto eter. Depen ing on the Review Questions.

type o ggreg ting gent use , curve th t c n be use to

ssess pl telet unction is obt ine .

In vivo, pl telets p rticip te in pri ry he ost sis by f rst

hering n then ggreg ting t the site o n injure bloo

vessel. Pl telet ggreg tion is contributing ctor to sub- CHAPTER HIGHLIGHTS

cute stent thro bosis. P tients un ergoing stent proce- Blood Vasculature: Structure and Function

ure re onitore to ssess the e ect o using spirin n

clopi ogrel, pro rug whose ctive et bolite selectively ■ Arteries h ve the thickest w lls o the v scul r syste .

inhibits ADP- epen ent pl telet ggreg tion. In vitro, pl te- ■ Veins re l rger n h ve ore irregul r lu en th n the

let ggreg tion ss ys use v rious pl telet ctiv tors to i en- rteries. In co p rison to rteries, veins re rel tively thin

ti y bnor l pl telet unction n to onitor ntipl telet w lle with we ker i le co t.

rug ther py. ADP, coll gen, epinephrine, ristocetin, n ■ Arterioles re the icroscopic continu tion o rteries.

r chi onic ci re re gents co only use to in uce Microscopic lly size veins re re erre to s venules.

pl telet ggreg tion. ■ Venules connect the c pill ries to the veins.