Transcript Preanalytical Issues

MLAB 1227-Coagulation
Keri Brophy-Martinez
Preanalytical Issues in Coagulation
Testing
Objectives
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Describe special precautions regarding specimen collection and
processing for coagulation testing and determine the
appropriateness of specimens.
State the type of anticoagulant tube used for coagulation testing.
Discuss the function of the sodium citrate anticoagulant in
coagulation testing.
Recognize the appropriate order of draw in terms of coagulation
testing.
State and apply the formula used to correct for high hematocrits.
Cite storage requirements for the prothrombin and activated
prothrombin time assays.
Define platelet poor plasma.
Define platelet rich plasma.
State the purpose of the blood to anticoagulant ratio in the
sodium citrate tube.
Sample Collection

Anticoagulant of choice
◦ 3.8% or 3.2% Sodium Citrate
 3.2 % Preferred as the standard measure due to
stability and closeness to the plasma osmolality
◦ Anticoagulant/blood ratio is critical (1:9)
 Exact amount of blood must be drawn. No short
draws are acceptable, this will falsely increase
results due to presence of too much anticoagulant
 CLSI guideline is 90 % of calibrated volume
◦ Purpose of the anticoagulant is to bind or chelate
calcium to prevent clotting of specimen
Sample Collection

Sidenote: Samples with High hematocrits
◦ CLSI recommends adjusting anticoagulant
ratio for patients with hematocrits exceeding
55%
◦ High hematocrits may cause falsely prolonged
test results due to an over- anticoagulated
sample
Correction Formula: High
Hematocrits
C= (1.85 x 10-3) (100-H)V
Where:
C= volume of sodium citrate
V=volume of whole blood drawn
H= patient’s hematocrit
Example:
Patient has a hematocrit of 60%, and blood is to be drawn into a 2.7 mL blue top-tube.
Patients Hct= 60%
V= 2.7 mL
C= (1.85 x 10-3)(100-60) * 2.7mL
= 0.2 mL
Site Selection

Untraumatic venipuncture is required
◦ Traumatic venipunctures release tissue factor
and initiate coagulation
Fingersticks/Heelsticks are not
recommended
 Indwelling IV line draws are discouraged

◦ Contain heparin
◦ Falsely increased results
Order of Draw

Evacuated tube system
◦ Blue top is 1st or 2nd tube.
◦ If 2nd tube drawn, 1st top must be
anticoagulant free (i.e. red top)

Butterfly system
◦ Discard tube must be utilized
 Why?
 To avoid clotting
 To rid specimen of air in the tubing which can cause an
inaccurate blood-anticoagulant ratio
Storage Requirements

Prothrombin Time: PT
◦ Uncentrifuged or centrifuged with plasma
remaining on top of cells in unopened tube
kept at 18-24 oC must be tested within 24
hours of collection

Activated Partial Thrombin Time: APTT
◦ Uncentrifuged or centrifuged with plasma
remaining on top of cells in unopened tube
kept at18-24 oC must be tested within 4
hours of collection
Storage Requirements

Other Assays
◦ Fibrinogen, Thrombin Time, Factor Assays
◦ Centrifuged with plasma remaining on top of
cells in unopened tube kept at 18-24 oC must
be tested within 4 hours of collection
Storage Requirements

Other general notes
◦ Perform coagulation tests ASAP
 Specimen may deteriorate rapidly (especially factors
V and VIII)
◦ If the testing is not completed within specified
times, plasma should be removed from the
cells and placed in a frost free freezer
 - 20 oC for two weeks
 -70 oC for six months
Transportation of Specimen
Send specimen on ice OR deliver to lab
ASAP
 Separate cells from plasma immediately
via centrifugation

Common Collection Problems
Error
Consequence
Comment
Short draw
<2.7 mL
PT/PTT falsely prolonged
Anticoagulant to blood ratio
exceeds 1:9
Failure to mix specimen after
collection
PT/PTT falsely prolonged
Blood clots form when
anticoagulant & blood do not
mix
Excess vigorous mixing
PT/PTT falsely shortened
Hemolysis and platelet
activation cause start of
cascade
Hemolysis
PT/PTT falsely shortened
Reject specimen
Improper storage: wrong
temperature or held too long
PT/PTT falsely prolonged
Must follow storage
requirements
Chilling in refrigerator or
placing on ice
PT falsely shortened
Chilling to 4 oC activates factor
VII.
Inadequate centrifugation
PTT loses sensitivity for lupus
anticoagulants and heparin.
Factor assays inaccurate
Desire platelet poor plasma
Prolonged tourniquet
application
Falsely elevates vWF, factor VIII
Tourniquet causes venous stasis
Common Collection Problems
(con’t)
Error
Consequence
Comment
Drawing coagulation tube
PRIOR to other
anticoagulant tubes
PT/PTT falsely affected
Contamination
Probing the vein
PT/PTT falsely shortened
Tissue thromboplastin is
released activating
coagulation
Heparin contamination from
line draw
PTT falsely prolonged
Heparin keeps the blood
from clotting
Lipemia
Test may not work
Photo-optical methods
affected
Icterus
Test may not work
Photo-optical methods
affected
Terms

Platelet –Poor plasma (PPP)
◦ <10 x 10 9 /L
◦ Specimen has been centrifuged for 15 minutes @ 1500 xg
◦ The reasons for plasma to be PP are:
 Contains platelet factor 4
 heparin neutralizer- results in falsely decreased results
 Contains phospholipid
 affects lupus anticoagulant and factor assay testing
 Results in a false normal result
 Contains factor 8 and von Willebrand antigen
 Results in falsely decreased results
Terms

Platelet-Rich plasma(PRP)
◦ Used in platelet function studies
◦ 200-300 x 10 9 /L
◦ Specimen has been centrifuged for 30 minutes
@ 50 xg
References
Castellone, D. (n.d.). Coagulation Dos and
Dont's. Advance for Administrators of Clinical
Laboratories, 13(1), 1-2.
 McKenzie, Shirlyn B., and J. Lynne.
Williams. "Chapter 40." Clinical Laboratory
Hematology. Boston: Pearson, 2010. Print.
