CORE Program:
Coagulation for the
Surgical Resident
Menaka Pai, BSc MD FRCP(C)
Hemostasis and Thrombosis Fellow
Department of Medicine, McMaster University
Karen A. Moffat, ART FCSMLS(D)
Technical Specialist, Coagulation, HRLMP
Lecturer, Department of Medicine, McMaster University
October 1, 2008
What We’ll Discuss
(taken straight from the POS objectives!)
• How normal hemostasis works
– Primary Hemostasis
– Secondary Hemostasis
– Specific abnormalities of hemostasis
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Platelet disorders
Hemophilia A and B
von Willebrand's disease
Disseminated intravascular coagulation
Drug effects
• How to predict hemostatic function
– Clinical methods
– Laboratory methods
• Cases
How normal hemostasis works
“If the bloodbath must come, then let's get on with it!”
- Gov. Ronald W. Reagan to the U.C. Board of Regents
Why don’t we bleed?
Series of inter-related processes…
• Primary hemostasis
– Interaction of von Willebrand factor and platelets
• Secondary hemostasis
– Through a series of reactions, prothrombin is
activated to thrombin, resulting in the conversion of
fibrinogen to fibrin and the formation of a fibrin clot
• Clot stabilization
– Activation of factor XIII to factor XIIIa by thrombin, in
the presence of fibrin
• Wound healing
– Delayed activation of the fibrinolytic system
Primary Hemostasis
STEP 1. ADHERE
Grab onto the vessel surface via von Willebrand’s factor
STEP 2. ACTIVATE
Turn into a sticky, thrombogenic entity
STEP 3. AGGREGATE Grab onto other passing platelets
Secondary Hemostasis:
Modified Waterfall Cascade
Updated Coagulation Cascade
Correction: Walsh PN. Biochemistry 2007,Nov 6; 46(44): 12886-12887
Intrinsic Pathway
XII
surface
HMWK
PK
XI
Extrinsic Pathway
XIIa
HMWK
Ca2+
VII
XIa
IX
VIII
IXa
Ca2+
PL
VIIIa
X
V
Va
X
Xa
Ca2+
PL
prothrombin
Fibrinogen
Vascular
injury
VIIa + TF
Ca2+
Fibrin monomer
thrombin
Fibrin polymers
Soluble fibrin
XIII
fibrin
XIIIa
Fibrin polymers
Insoluble fibrin
Clot Stabilization
http://www.ebi.ac.uk/interpro/potm/2006_11/Page1_files/image012.jpg
How can hemostasis go wrong?
• Primary hemostasis
– Platelet disorders
– von Willebrand's disease
– Cardiopulmonary bypass
• Secondary hemostasis
– Hemophilia A and B
– Disseminated intravascular coagulation
• Clot stabilization
– Cardiopulmonary bypass (again!)
How can hemostasis go wrong?
• Drug effects
– ASA
– nonsteroidal anti-inflammatory drugs
– dipyridamole (Persantine®)
– GPIIb/IIIa inhibitors
– warfarin sodium (Coumadin®)
– heparin
– alcohol
– corticosteroids
How to predict hemostatic function:
Clinical Methods
“Predicting the future is a very difficult business indeed.”
- Albus Dumbledore, Harry Potter and the Prisoner of Azkaban
Problem #1:
Bleeding disorders are rare,
but bleeding is common!
• Up to 50% of normal, healthy people consider
themselves easy bruisers/bleeders
– Nosebleeds
– Gum bleeds
– Easy bruising
• 1979 study used a self-assessment questionnaire:
– 35% of patients with vWD had a “negative” bleeding history
– 23% of controls had a “positive” bleeding history
Miller CH et al. Optimal assignment of heterozgous genotype of classic von Willebrand’s disease by discriminant analysis. Blood 54:137, 1979.
Problem #2:
Patients who have never bled before
may bleed in your OR
• Patients with mild bleeding disorders may not bleed
until you “challenge” them
• Patients with a negative bleeding history may acquire
a bleeding problem later in life
• The bleeding history is only 65% sensitive and 77%
specific
How do we predict
hemostatic function?
• We need an approach to separate those with…
– A low risk of having a bleeding disorder
– A high enough risk of having a bleeding disorder to
warrant further diagnostic workup
• This approach must be…
– Easy-to-use
– Powerful
– Efficient and cost-effective
• Combine lab tests and a clinical history
Adapted from Lillicrap et al. Haemophilia 2006.
We don’t have a validated
questionnaire (yet)
• There is only one validated bleeding score,
for type I vWD
• This score is not widely applicable, since
there are many other bleeding disorders
– Inherited platelet abnormalities (secretion, isolated or
combined aggregation, dense granule deficiency)
– Acquired abnormalities (bone marrow disorders, drugs,
thyroid, Cushing’s, connective tissue, liver, renal)
– Fibrinogen abnormalities
Lee CA. Semin Hematol 1999.
Hayward CP. Curr Opin Hematol 2003.
Quiroga T et al. J Thromb Haemost 2004
Philipp CS et al. J Thromb Haemost 2003.
Cattaneo M. J Thromb Haemost 2003
Rodeghiero F. Thromb Haem 2005.
Ask your patients about
“clinically significant bleeding”
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•
•
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Spontaneous GI bleeding
Spontaneous hemarthrosis or following a minor trauma
Prolonged bleeding from trivial wounds (>15 minutes or
recurring spontaneously after 7 days)
Bruising, with minimal or no apparent trauma, especially with a
lump under the bruise?
Spontaneous nosebleeds that lasted >10 minutes or needed
medical attention?
Heavy, prolonged, or recurrent bleeding after dental extractions
that needed medical attention?
Heavy, prolonged, or recurrent bleeding after surgical
procedures
Ask your patients about
“clinically significant bleeding”
•
•
Anemia requiring treatment or blood transfusion
For women, heavy menses
–
–
–
–
•
•
clots >1 inch in diameter and/or
changing a pad or tampon >hourly and/or
resulting in anemia or iron deficiency and/or
requiring medical or surgical treatment
Always ask about blood relatives with a bleeding disorder!
Always take a general medical and drug history!
How to predict hemostatic function:
Laboratory Methods
“Predicting the future is a very difficult business indeed.”
- Albus Dumbledore, Harry Potter and the Prisoner of Azkaban
Several Lab Strategies Exist
• Tests that look at parts of hemostasis
– PT, aPTT, TT, fibrinogen
– Platelet count
• Tests that look at all of hemostasis
– Bleeding time
– Platelet function analyzer (PFA-100®)
– TEG
Sample Collection and Transport
• 3.2% trisodium citrate is recommended
– 3.8% sodium citrate results in longer clot times
• 9:1 ratio of whole blood to anticoagulant
• Transport should be at room temperature
– Ideally received within 1 hour of collection
• Samples from patients on UFH should be centrifuged
within 1 hour of collection
CLSI, H21-A5, Vol. 28 No. 5, Jan. 2008
Prothrombin Time
• Assesses factors VII, X, V, prothrombin and
fibrinogen
• One-step reaction
Examples of TF
•Recombinant human
•Recombinant rabbit
•Human placenta
Tissue factor activator
2 parts PT
reagent
1 part plasma
Source of calcium
Source of phospholipid
Heparin neutralizer
Time for clot formation
International Normalized Ratio
PT in seconds of the patient
PT in seconds of the geometric
mean of the normal range
ISI
ISI = International Sensitivity Index
• Indicates reagent sensitivity to the Vitamin K
dependent factors assessed in the PT
– specifically factor II, VII and X
• Inverse relationship
Causes of an elevated PT
With normal APTT
With ↑ APTT
„Isolated
„Warfarin
factor VII
deficiency – congenital
or acquired
„Early
warfarin therapy
„Early vitamin K
deficiency
„Early liver disease
therapy
„Vitamin K deficiency
„Liver disease
„Deficiency of factor X, V or
prothrombin
„Heparin (gross) or a direct
thrombin inhibitor
„Dilutional coagulopathy
„Intravascular coagulation
„Lupus anticoagulant
„Hypofibrinogenemia
(severe)
Activated Partial Thromboplastin Time (APTT)
• Assesses high molecular weight kininogen,
prekallikrein and factor XII, factors XI, IX, VIII, X,
V, prothrombin and fibrinogen
• 2 step reaction
Contact factor activators:
•Ellagic acid
•Silica
•Kaolin
Step 1
1 part APTT
reagent
1 part plasma
Activator
Source of
phospholipid
Incubate at 37°C
for predetermined time
1 part calcium
1 part APTT
reagent
1 part plasma
Step 2
Time for
clot
formation
Important considerations
• APTT reagents should be assessed for
sensitivity to:
– Intrinsic factor levels
– Lupus anticoagulants
– Heparin
• Different APTT reagents have different
sensitivities
APTT Reagent Sensitivity to Lupus Anticoagulants
APTT Ratio for LA sample
results are shown as ratios of:
LA positive plasma APTT / mean APTT for 5 normal reference samples
5
1 - ellagic acid
4.5
2 - ellagic acid
4
3 - ellagic acid
3.5
4 - ellagic acid
3
2.5
5 - silica
2
6 - micronized silica
1.5
7 - micronized silica
1
0.5
8 - ellagic acid
0
0
1
2
3
4
Lupus Anticoagulant Positive Plasma Sample Number
5
9 - colloidal silica
10 - silica
Causes of an elevated APTT
Factor
Deficiency*
Clinically Significant
Clinically Insignificant
„Factor
„Factor
VIII
„Factor IX
„Factor XI
XII
„Prekallikrein
„High molecular weight
kininogen
*could be a single or multiple factor deficiency
Inhibitors
„Lupus
anticoagulant
e.g. thrombosis
„Specific factor
inhibitor
„Heparin
„Lupus
anticoagulant
e.g. acute infection
Relative prevalences to consider
Lupus anticoagulant
(hospitalized patients)
~1 / 20
Mild factor XII deficiency
~1 / 200
Factor VIII deficiency
Factor IX and factor XI
deficiency
~1 / 5000 males
even rarer
Thrombin Clotting Time (TT)
• Assesses the time for fibrinogen to convert to
fibrin after an exogenous source of thrombin
is added to the plasma
• Test not standardized
– Variables: calcium and concentration of thrombin
– References ranges vary
• Common uses for the TT
– Qualitative assessment of fibrinogen and its
function
– Check for heparin
Causes of a prolonged TT
Reason
Cause
Quantity issue
Hypofibrinogenemia or
afibrinogenemia
Quality issue
Dysfibrinogenemia
Inhibition of test reagent
Presence of UFH or a direct
thrombin inhibitor
Interference with
polymerization of fibrin
monomers
„Presence
of elevated fibrin
degradation products
„Presence of a paraprotein
Heparin confirmation
• Addition of Protamine Sulphate
– Positive charge neutralizes the negatively
charged heparin
– TT shortens
Fibrinogen
• Clauss method
– Strong thrombin concentration (100 U/mL)
is added to a dilution of patient plasma
– The clotting time is inversely proportional
to the fibrinogen concentration
– A reference plasma with a known
concentration of fibrinogen is used to
develop the calibration curve
Some considerations for the investigation
of abnormal coagulation results
Are one, two or three screening tests abnormal?
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•
•
One test
– PT only – ? Factor VII
– APTT only – ? Factor VIII, IX, XI, XII, PK or HMWK
– TCT only – ? fibrinogen
Two tests
– PT and APTT – ? common pathway, fibrinogen
– APTT and TCT – ? Heparin
Three tests
– PT, APTT, TCT - ? Consumption, liver disease,
hypofibrinogenemia (severe) / afibrinogenemia
• MIXING STUDIES ARE REQUIRED
Immediate mixing studies
• 1 part normal platelet poor plasma + 1
part patient plasma
• Repeat abnormal test – PT or APTT
Normal plasma
– Approximately 1.0 U/mL of all factors
– After mixing, minimum of 0.50 U/mL of all
factors
Interpretation of mixing
studies
• Full correction into the reference range
– Suggestive of a factor deficiency
• congenital or acquired
– Caution: does not rule out specific inhibitor!
• No correction into the reference interval
– Suggestive of an inhibitor
• Lupus anticoagulant (non-specific inhibitor)
• Specific inhibitor (most common: Factor VIII
A brief word:
Bleeding Time
• Used since the 1900s to screen for platelet
function abnormalities and vWD
– Standard incision on forearm
– BP cuff inflated to 40 mmHg to standardize
intracapillary pressure
– Blot wound with filter paper q 30 seconds to see if
bleeding has stopped
Cons of the Bleeding Time
• Sensitivity and specificity are poor
– Affected by many unpredictable factors
– Doesn’t pick up mild defects
– Imprecise endpoint
• With no history of bleeding disorder, BT is not
a useful predictor of perioperative bleed
• We do not recommend this test be performed
routinely!!!
Gewirtz et al. Clinical usefulness of preoperative bleeding time. Arch Pathol Lab Med 1996.
Rodgers RP et al. A critical reappraisal of the bleeding time. Semin Thromb Hemost 1990.
Putting It All Together
“A pint of sweat will save a gallon of blood.”
- General George S. Patton
The Clinical History
• Many questions are useful to predict a
patient’s risk of having a bleeding
disorder
• We are working on a streamlined
questionnaire that you can use to make
the history more reliable and efficient
The Laboratory Tests
• The CBC, PT and aPTT are highly
reproducible, automated and inexpensive on
an individual basis
• They have become part of the routine panel
of lab investigations for surgical and
nonsurgical patients
A Word of Caution
• These lab tests were designed to measure
factor deficiencies
– ie. Hemophilia
– ie. Heparin protocols
• They weren’t designed to predict bleeding
– We must understand their limitations
– We must generate a pretest probability of a
hemostatic problem first
Cons of the routine PT and aPTT:
The Nonsurgical Patient
• Abnormal Test ≠ Abnormal Patient
• 100 consecutive patients with long aPTT
– 50% had normal factor assays
– 50% had abnormal factor assays
• Degree of factor abnormality didn’t predict bleeding
Kitchens CS. Prolonged activated partial thromboplastin time of unknown etiology.
Am J Hematol. 1988 Jan;27(1):38-45.
Cons of the routine PT and aPTT:
The Nonsurgical Patient
• It may not add much to the clinical history
– <1% of patients with no bleeding Hx have abnormal PT
• Routine measurement is expensive in the
aggregate
– 81% of medical pts have admission PT/PTT
– 70% of tests not clinically indicated
– Inappropriate PT/PTTs cost UPenn's medical
service $61,000 in 1989
Robbins JA et al. Partial thromboplastin time as a screening test. Ann Intern Med. 1979.
Erban SB, Kinman JL, Schwartz JS. Routine use of the prothrombin and partial thromboplastin times. JAMA. 1989.
Cons of the routine PT and aPTT:
The Surgical Patient
• A high INR may not predict bleeding
• 2006 systematic review
– Elevated INR (>1.5) not predictive of
periprocedural bleeding in bronchoscopy,
central line insertion, femoral angiogram,
liver Bx
Segal JB, Dzik WH. Transfusion. 2005 Sep;45(9):1413-25.
Cons of the routine PT and aPTT:
The Surgical Patient
• A high aPTT may not predict bleeding
• Questionnaire given to 2000 surgical patients
– High bleeding risk = known coagulopathy, liver
disease, malabsorption, malnutrition, trauma,
previous hemorrhage
• High risk patients? 1.7% postop bleed
• Low risk patients? 0.22% postop bleed
• aPTT added no additional info to this pretest
probability (LR = 1)
Bottom Line
• Combine a thorough bleeding history
with carefully selected lab tests
• Refer your patient to us if you have any
concerns
• Hematology and laboratory medicine
are here to help!
Cases
“Practice makes perfect!”
- Menaka and Karen
Case # 1
• A 26 year old male taken to the Hamilton
General Hospital’s ER after an MVA
• Multiple blunt and penetrating traumatic
injuries, including CT evidence of head injury
• One hour after MVA, bloodwork is drawn:
– PT/INR 2.3
(0.8 – 1.2 INR)
– APTT
44 seconds (22-35 seconds)
– TCT
108 seconds (20 – 30 seconds)
• Summarize the abnormalities, and tell us
what you want to do next!
Case # 1
Additional laboratory results
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Fibrinogen 0.6 g/L (1.6 – 4.2 g/L)
D-dimers
Positive
Hemoglobin 154 g/L
Platelets
163 x 109/L
Schistocytes on blood film
• What’s going on?
Management of DIC
• Diagnosis
– Draw basic coagulation tests and a CBC
– Look for oozing from line sites
– Look for underlying disease
• Treatment
– Treat underlying disease
– No evidence for blood products in patients who
are not bleeding or who are not at high risk of
bleeding.
– If bleeding, give platelets (<50 x 109/L), FFP (INR
or PTT abnormal), cryoprecipitate (Fib <1 g/L)
Case # 2
• 62 year old female seen in outpatient
Hematology Clinic.
• TKA scheduled for October 30th, 2008
• Orthopedic surgeon alarmed by recent
“routine bloodwork” done by family doc
– PT/INR
– APTT
– TCT
1.1
(0.8 – 1.2 INR)
46 seconds (22-35 seconds)
23 seconds (20 – 30 seconds)
• Summarize the abnormalities, and tell us
what you want to do next!
Case # 2
Additional laboratory results
U/mL (RI: 0.50 – 1.50 U/mL)
Factor II Biological
1.43
Factor II Echis
1.44
Factor V
0.95
Factor VII
1.23
Factor X
1.35
Factor VIII
1.54
Factor IX
0.89
Factor XI
0.82
Factor XII
0.12
Management of fXII deficiency
• Not associated with clinical bleeding!
• Do not give these patients empiric therapy if
they are not bleeding
Case # 3
• 58 year old female in day surgery unit.
Gastric bypass surgery in 4 hours.
• Past history:
– Tonsillectomy at age 8 – no bleeding
– Dental procedure at age 22 – “oozed” for 3 days
– Hysterectomy at age 52 – required 3 units of
pRBCs
– Menarche at age 13 – “my periods weren’t any
heavier than my mother’s or sisters’ periods”
– 3 vaginal childbirths – no bleeding
– “Easy bruising” – orange-sized bruises that track
downwards
• Tell us what you want to do next!
Case #3:
Urgent Laboratory Workup
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•
•
•
INR
APTT
fVIII:C
VWF:RCo
0.9
(0.9 – 1.2 INR)
44 seconds (26-38 seconds)
0.14 U/mL
(0.50–1.50 U/mL)
<0.10 U/mL (0.50 – 1.50 U/mL)
• Summarize the abnormalities, and tell us
what you want to do next!
Management of vWD
• One of the commonest bleeding disorders
• Due to abnormalities in VWF
– QUANTITATIVE (Type 1 and Type 3)
– QUALITATIVE (Type 2)
• Diagnosis
– Draw basic coag tests, a CBC and a vWD panel
– Ask about mucosal bleeding
• Treatment
– DDAVP
– Humate P
Validated in mild and severe
bleeding disorders
They have limitations too
Adapted from Lillicrap et al. Haemophilia 2006.
Order with caution!
They have limitation
The End!
PFA-100
• Blood aspirated through capillary tube
• Blood encounters:
– CEPI (collagen + epinephrine) cartridge
– CADP (collagen + ADP) cartridge
• If platelet adhesion, activation and
aggregation occur, tube is occluded and
blood flow stops
• Time for blood flow to stop = "closure time"
Pros of PFA-100
• Simple, rapid way to assess blood in
“realistic” high shear stress conditions
• Assesses both…
– vWF function
– Platelet function
• Is not affected by factor levels
Cons of PFA-100
(Platelet Physiology Subcommittee of ISTH-SSC)
• Influenced by many unpredictable factors
• Interlab variability, because each lab must
establish its own reference range
• Normal CT excludes rare severe disorders
– Glanzmann, Bernard-Soulier, severe vWD
• Not sensitive for common disorders
– Mild vWD, platelet disorders
Hayward et al. J Thromb Haem 2006.
Thromboelastograph (TEG)
• Invented 59 years ago to evaluate clotting in
"real time," and assist with surgical
hemostasis
• Small studies describe its use in transplant,
CV surg, trauma, neurosurg, DVT, drug
monitoring (GPIIb/IIIa inhibitors, rfVIIa)
• Renewed interest in its role in “surgical blood
management” decision aids
Principles of TEG
Measures viscoelastic changes associated with fibrin polymerization
Different TEG Patterns
Pros of TEG
• Truly global “real time” view of
hemostasis
• Lots of experience using it in surgery
– Though no large, randomized trials
• Some experience using it to monitor
therapy for bleeding disorders
Cons of TEG
• Little experience using it to screen for
bleeding disorders
• Lack of correlation with standardized lab
variables
• Huge variability of technique between
labs
aPTT has poor test
characteristics in this population