Page 572 - Clinical Hematology_ Theory _ Procedures ( PDFDrive )

556 PART 7 ■ Principles and Disorders of Hemostasis and Thrombosis

ore severe in atients with acquire von Wi ebran ’s is-
von Willebrand’s Factor

TABLE 28.5 Requirements for Primary ease. B ee ing ro ucous e branes is ore co on
an ref ects the uch ower eve s o vWF activity in these
Hemostasis
in ivi ua s. vWF activity is ty ica y 20% or ess o nor a .

Activity Interaction Reaction
Pseudo–von Willebrand’s Disease

Plasma vWF Subendothelial Platelet contact T is is a rare isor er in which atients rese b e those with

deposition interaction von Wi ebran ’s isease because o ow eve s or absence o

with GP Ib arge u ti eric or s o vWF in the as a. Patients with

Platelet vWF Binding to GP IIB/IIIa Platelet spreading seu o–von Wi ebran ’s isease have a ate et abnor a ity

subendothelial surface in which s ontaneous ate et aggregation occurs. Low eve s
o arger u ti ers resu t ro increase consu tion ur-
Platelet-platelet Platelet
interaction aggregation ing ate et aggregation.

vWF, von Willebrand’s factor. Increased Levels of vWF

Increase eve s o vWF have been associate with stress,

inf a ation, ostsurgica states, regnancy, rena isease,
is a so ecrease in ro ortion to the ecrease in vWF. In

these cases, the b ee ing is cause by insu cient eve s o iabetes, rheu atoi isor ers, sc ero er a, an Raynau

circu ating vWF an actor VIII. B ee ing ani estations are heno ena. vWF ay be an in icator o vascu ar en othe-

ess severe in atients who have a nor a concentration o ia status. Drugs such as 1- ea ino-8-d-arginine vaso res-

ate et vWF than in others ( ab e 28.5). sin (DDAVP), steroi s, an hor ones ay a so resu t in

In a atients whose vWF shows ow ristocetin co actor e evate eve s o vWF.

activity, exce t or those esignate as having ty e B isease, Laboratory Findings

the vWF has an abnor a u ti eric structure an there is

a ecrease in or absence o the arge u ti ers. T e o owing aboratory resu ts are ty ica o von

y e II is characterize by structura y abnor a vWF. Wi ebran ’s isease:

T e circu ating eve s o vWF ay be ecrease or nor a , ■ B ee ing ti e: i y to o erate y ro onge

an VIII:C ay be a ecte si i ar y. y e IIA an ty e IIB ■ P ate et retention: ty ica y ecrease

are autoso a y o inant, whereas ty e IIC is recessive. ■ P ate et agg utination: ristocetin—abnor a

Patients with ty e III, the ost severe or o von ■ P ate et aggregation: nor a with a but ristocetin

Wi ebran ’s isease, are ike y to have a ajor e iso e o ■ vWF unction (ristocetin co actor activity)

b ee ing ear y in i e because signi cant y ecrease a ounts

o vWF an VIII:C are ro uce . Genetica y, they are thought Quantitation o vWF antigen (vWF:Ag) can be eter ine

to be ho ozygous or oub e heterozygous. T ese atients by i unoe ectro horesis. T ese assays easure tota

robab y co rise a se arate grou because o the ty ica y a ounts o vWF rotein, in e en ent o its abi ity to unction.

recessive o a ity o genetic trans ission ( ab e 28.6). Fina y, vWF u ti eric ana ysis is use u in istinguishing
between subty es an in eter ining thera eutic anage-

Acquired von Willebrand’s Disease ent. vWF u ti eric ana ysis uses so iu o ecy su ate

(SDS) agarose ge e ectro horesis an ra io abe e antibo y to
von Wi ebran ’s isease is occasiona y seen as an acquire

con ition. Associations have been a e with u us erythe- visua ize the i erent o ecu ar weight u ti ers.

atosus an other autoi une isor ers as we as ye o-

ro i erative isor ers. T e resence o a circu ating antibo y NOTE: This is a good time to review the de nitions of Key

to vWF ay be i icate in so e cases. Another echanis Terms in the Glossary and ash cards on . This is

res onsib e or ecrease a ounts o vWF in acquire states also a good time to complete Review Questions related to

is the absor tion o the coagu ation co onent onto abnor- the preceding content.

a ce sur aces. He orrhagic co ications are genera y

TABLE 28.6 Clinical Features of Various Types of von Willebrand’s Disease

Type Bleeding Time Bleeding Tendency Petechiae Hemarthrosis *

I Normal or increased Mild None Uncommon

II Increased Moderate Usually none Uncommon

II Increased Often severe Occasionally Uncommon

* Only occurs in the most severely affected.