Page 553 - Clinical Hematology_ Theory _ Procedures ( PDFDrive )

CHAPTER 27 ■ Principles of Hemostasis and Thrombosis: Blood Coagulation Factors and Natural Coagulant Systems 537

1. Speci c Factor Inhibitors e ication history nee to be reviewe . A itiona

I the AP screening test is ro onge with a nor a AP , with he arin assay (anti-Xa inhibition assay) can be use to

i e iate ix an AP incubate ix, this in icates a exc u e the resence o anticoagu ants.

actor e ciency in the intrinsic or na co on athway.

I the ro onge AP screen is ue to the resence o an Chrom ogenic Anti-Xa

inhibitor, ixing with an equa vo u e o nor a atient T e chro ogenic anti-Xa etho or onitoring ow–

as a wi not shorten or correct the ro ongation o AP o ecu ar weight he arin (LMWH) an un ractionate

resu ts. T ere is no shortening or correction in the AP he arin is another assay. T is auto ate assay can re ace

resu t. Inhibitor in the atient’s as a is resent in excess the AP or onitoring un ractionate he arin because it

an bin s to coagu ation actors or rotein/ hos ho i i e i inates the variabi ity seen with AP resu ts.

co exes in both the atient’s as a an nor a atient Chro ogenic assays use a actor Xa substrate onto which

as a. a chro o hore has been inke . Factor Xa c eaves the chro-

o istinguish the ocation o a s eci c actor e ciency, ogenic substrate, re easing a co ore co oun that can

the AP resu ts can be ana yze in conjunction with P be etecte with a s ectro hoto eter an is irect y ro-

resu ts. I the P is nor a , this suggests an intrinsic athway ortiona to the a ount o activate actor X (FXa) resent.

e ciency (VIII, IX, XI, XII, PK, HMWK). I the P is ro- When a known a ount o actor Xa is a e to as a con-

onge , this suggests a co on athway e ciency ( brino- taining he arin (or LMWH), the he arin enhances actor Xa

gen, II, V, X). inhibition by antithro bin ren ering ess actor Xa avai ab e

I the AP Screen is ro onge , with a nor a AP to c eave the substrate. T e test resu ts in the or o a stan-

i e iate ix o an equa vo u e o nor a atient as a ar curve with known a ounts o he arin can be use to

but an abnor a AP incubate ix o an equa vo u e eter ine actor Xa.

o nor a atient as a, this in icates the resence o a So e a vantages o the anti-Xa he arin assay co are

e aye inhibitor such as s eci c actor inhibitors, ost to the AP are

co on y actor VIII inhibitor. So e inhibitors wi e -

onstrate a e aye ty e inhibitor attern, with ti e an /or ■ Una ecte by un er e b oo co ection tubes

te erature e en ence. ■ Not susce tib e to inter erence ro e evate concen-

A though rare, the resence o a actor inhibitor, such as a trations o actor VIII or brinogen ro acute- hase

actor VIII inhibitor, wi increase the risk o i e-threatening reactions

b ee ing. T e resence o a actor inhibitor can be con r e ■ Not inf uence by actor e ciencies ( ossib e exce tion

by a Bethes a assay or that actor. is A e ciency)
■ No nee to estab ish an AP thera eutic range

2. Nonspeci c Inhibitors So e isa vantages o the anti-Xa he arin assay co -

I the AP Screen is ro onge with an AP i e iate are to the AP are

ix o an equa vo u e o nor a atient as a an ro-

onge with the AP incubate ix o an equa vo u e o ■ High cost

nor a atient as a, this suggests a nons eci c inhibi- ■ Processing o s eci en within 1 hour to avoi he arin

tor. T e resence o ow- eve nons eci c inhibitors in the neutra ization ro PF4

atient’s as a ay e onstrate an AP incubate ix ■ Questionab e thera eutic range i itations

si i ar to a e aye ty e inhibitor. ■ No sa ety an e ectiveness ata on outco es or anag-

T e resence o u us anticoagu ants, antibo ies against ing thera y

rotein- hos ho i i co exes, wi increase the risk o

thro boe bo is . I the c inica history suggests u us anti- Classic Assays for Coagulation Factors

coagu ant (LA), urther testing inc u es hos ho i i -base Tese assays ay be con ucte in certain circu stances:

screening tests, hos ho i i e en ency assays, an exc u-

sion o the resence o inhibitors in a ition to the ixing 1. One-stage quantitative assay or actors II, V, VII, an

stu y inc u ing an incubate AP . X. T is assay uses age seru an absorbe as a in

the P . Age seru contains actors VII, IX, X, an XII.
3. Anticoagulants Absorbe as a contains actors V, VIII, XI, an XIII.

I the AP Screen is ro onge with an AP i e iate Te P is con ucte using s eci c actor– e cient as a

ix o an equa vo u e o nor a atient as a an ro- with s eci c i utions o atient as a. T e ercentage

onge with the AP incubate ix o an equa vo u e o o actor activity is otte to construct an activity curve.

nor a atient as a, anticoagu ants are a ossibi ity. 2. One-stage quantitative assay or actors VIII, IX, XI, an

T e resence o the anticoagu ants such as he arins, XII. T is roce ure is base on the AP assay. It is base

on a arinux, abigatran, or other irect thro bin inhibi- on the resu ts o atient as a to correct s eci c ac-

tors can cause ro ongation o both the AP i e iate tor– e cient as a. T e resu ts are ex resse in ercent

ix an AP incubate ix. T e atient’s e ica an activity on an activity curve.