Beware the APTT
AIMS National Scientific Meeting- Darwin
24-27 September 2012
Olivia Yacoub
Haemostasis and Thrombosis Laboratory
What is the APTT?
APTT
PT
Time to form Fibrin clot
(seconds)
Kamal etal. Mayo Clin Proc. 2007;82(7):864-873
1
Ideal conditions: Pre-analytical
• Venepuncture without trauma
• IV line flushed of heparin
• Correct tube draw order
o
o
o
o
Appropriate mixing
3.2% citrate to correct fill line
Optimal transport (temperature sensitive!)
Centrifuged & tested within 4 hours of
collection
CLSI Collection Transport and Processing of Blood Specimens for Testing Plasma Based Coagulation Assays and Molecular Hemostasis
Assays: Approved Guideline. 5th edition H21-A5. Wayne: Clinical and Laboratory Standards institute; 2008
Sample fault vs. effect
Issue
Effect
EDTA plasma
Prolonged PT & APTT
Heparin contamination
Under-filled primary citrate tube
Serum / clotted sample
Partially clotted sample
Prolonged or shortened PT & APTT
Adapted from Favoloro et al, Lab Medicine, 2012; 43
2
Pre-analytical variables
Issue
Effect
Refrigerated whole blood
Platelet activation
Loss of FVIII, VWF
Delayed transport
Loss of labile factors esp FV FVIII
Prolonged PT, APTT
Poor centrifugation
Falsely low APTT
Adapted from Favoloro et al, Lab Medicine, 2012; 43
Prolonged APTT
Artifact
Repeat
Abnormal
Normal
? Anticoagulated or Systemic
No
Yes
Further investigation
Lupus
Factor assays
3
Investigation strategy APTT
• Assess urgency
• Acute / Chronic
• Clinical notes
• Anticoagulated
– Heparin, warfarin, DTI, AXA
• Bleeding
/
Clotting
• Previous results
• Acquired
/
Inherited
Common causes of elevated
APTT
• Disseminated
Intravascular
Coagulation (DIC)
• Anticoagulants
• Lupus inhibitor
(Antiphospholipid
syndrome)
•
• Factor deficiencies
– Liver dysfunction
– Vitamin K
deficiency
– Haemophilia
• Inhibitor
– Von Willebrand
disorder
Volume 33 No. 1 MayoMedicalLaboratories.com/communique
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CONTACT PATHWAY
XII
XIIa
Heparin
Antithrombin III
XI
XIa
IX
IXa
X
Xa
II
IIa
FIBRINOGEN
FIBRIN
Hepzyme -APTT
Screening test
APTT BEFORE AND AFTER HEPZYME TREATMENT
350
250
300
APTT (SECONDS)
TCT (SECONDS)
TCT BEFORE AND AFTER HEPZYME TREATMENT
300
200
150
Before Hepzyme
100
After Hepzyme
50
250
200
Before Hepzyme
150
After Hepzyme
100
50
0
0
0
0.2
0.4
0.6
0.8
HEPARIN CONCENTRATION (UNIT/ML)
1
1.2
0
0.2
0.4
0.6
0.8
1
1.2
HEPARIN CONCENTRATION (UNIT/ML)
5
Causes of prolonged APTT
• Lupus anticoagulant
– Group of antibodies that bind phospholipid or
phospholipid binding proteins
– Thrombosis: paradox increased APTT
– Depends on sensitivity of APTT reagents
– Clinical indications for ordering test
• Miscarriage
• Thrombosis
Test
Result
Reference
range (IMVS)
INR
2.0
0.9-1.2
APTT
46
24-38 sec
FVII
65
70-130 IU/dL
FVIII
299
60-180 IU/dL
FIX
54
60-160 IU/dL
FX
15
70-120 IU/dL
GGT
118
<60
LD
257
110-230
6
Liver dysfunction
“The defect in coagulation in patients
with chronic hepatocellular disease is
rarely due to a single abnormality.
Like others (Kupfer et al, 1963) we
have found the clotting and bleeding
times to be of little value. We have
confirmed that reduction of factors V,
VII, IX, and prothrombin may exist.”
DONALDSON,J etal; Clin. Path. (1969), 22, 199-204
FVIII sensitivity- Patient data
APTT (sec)
60
40
20
0
0
10
20
30
40
50
60
One-stage FVIII (IU/dL)
7
FVIII sensitivity- Spiking study
FVIII sensitivity
80
70
aPTT (sec)
60
50
40
30
20
10
0
0
20
40
60
80
100
FVIII (IU /dL)
y = 73.238x
R2 = 0.9931
Choong,C. Flinders Medical Centre, 2012
Case
• 80 year old, active female
• History
– January: Urticaria- allergy testing
– April: Chronic cough
– July: Back pain ? UTI
– August: repeat UTI testing -neg
– September: A+E severe back pain
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CASE HISTORY
– DAY 1
• A+E: Back pain, L limb
weakness, wt loss
• ?UTI
DAY
– DAY 2
• ? Bleed
– DAY 4
• CT: Haematoma Ilicacus
– DAY 5*
• INR=1.0
• Unexplained bruising hip +
thigh
• Transfused
– DAY 8
• 2° bruising, haematoma
• Bruising both arm
• Haematoma torso
+abdomen
• Severe back pain
Hb
(115‐155g/L)
WCC
(4‐11x10`9/L)
1
102
27
2
86
21
5*
71
12
6
87
8
117
*First time INR was ordered
Case Diagnosis
DAY 12
• Haematologist consulted
– Patient transferred to RAH
• APTT
• Platelets
• Haemoglobin
85
sec
337 x10 ^9 /L
87 g/L
(24-38)
(150-400)
(135-175)
• Normal renal / liver function
• Normal DDimer and fibrinogen
• Lupus anticoagulant not detected
9
50:50 Mix- Immediate
APTT
(sec)
51.1
Patient
plasma
Normal
plasma
31.8
50% Patient
50% Normal
38.1
Immediate mixing study
50:50
10
Mixing study - Incubated
Further testing
• Factor VIII
<2
IU/dL
(60-180)
• Factor IX
• Factor XI
• Factor XII
124
80
64
IU/dL
IU/dL
U/dL
(60-160)
(60-160)
(50-170)
• Factor VIII Inhibitor
9.0
Bethesda Units/ml
– Moderately strong inhibitor to Factor VIII detected
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Time to form Fibrin clot
(seconds)
Kamal etal. Mayo Clin Proc. 2007;82(7):864-873
Haemophilia A
FVIII
•Genetic X-linked
•Acquired
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Acquired Haemophilia
• Clinical bleed
– +/- unexplained bleeding
– Often delayed diagnosis
• FVIII low
• APTT when FVIII ~ 45% of normal
– APTT not always abnormal
• Normal INR, fibrinogen D-Dimer
• Lupus negative
AH- Clinical Presentation
• Bruising or soft tissue bleeding
• Severe muscle bleeding
• Haematuria, Epistaxis, GI bleeding, Intracerebral
bleeds
• Associated risk factors
–
–
–
–
–
Elderly
Postpartum
Autoimmune diseases
Cancer or precancerous
Drug induced
http://asheducationbook.hematologylibrary.org/cgi/content/full/2006/1/432
Accessed 30/8/11
13
Acquired Haemophilia in South
Australia (2003-2008)
•
•
•
•
•
Incidence 1-2 /million/year
Median age 78
Equivalent M/F ratio
Presentation inhibitor level ~2.5-11 BU/mL
Severe life threatening bleeds
– Mortality 8-22%
Tay etal. Seminars in Thrombosis and Hemostasis. 2009; 35:8
Conclusion
• “We’re not fussy”
– the samples are
• “We’re not challenging”
– the tests requests are
• Method behind madness
–
–
–
–
abnormal beware
normal beware
test selection crucial for diagnosis
priority/ line of testing case dependent
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Look before you leap.
Consequences can be painful!
Beware the APTT
Actually
Pretty
Tough
Test
15
Elizabeth Duncan
Sue Rodgers
Haemostasis Lab Staff IMVS
Pre-analytical variables
– Handling
– Transportation
– Processing
– Storage
– Correct test ordered
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Tests
• Repeat test
• INR/ APTT/ Fibrinogen/ DDIMER
• TCT
• Hepzyme
• Factor assays: FVIII, FIX, FXI, FXII
– Inhibitor screen
• Mixing study
Common presentation
Acquired Haemophilia
• Purpura or soft tissue bleeding
• Severe muscle bleed
–
–
–
–
–
–
–
–
–
Haematuria
Epistaxis
GI bleed
Intracerebral bleed
Uncommon; Haemarthroses
Post partum
Autoimmune disease
Cancer
Drug induced
Alice and Carrizosa. Hematology 2006 2006:432-437; doi:10.1182/asheducation-2006.1.432
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http://www.practical-haemostasis.com/Screening%20Tests/aptt.html
Acquired Haemophilia
Mortality
• Mortality 8-22%
– Uncontrolled bleeding
– 87% hemorrhage or bleeding requiring
transfusion
– Life threatening common in first weeks
of presentation
– Muscle bleeds- compartment syndrome
and tissue death
Green D, Lechner K. Thromb Haemost. 1981;45:200–203.
Morrison etal. Bood. 1993;81:1513–1520.
Hay etal. Thromb Haemost. 1997;78:1463–1467.
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Effects of sample type
Routine coagulation tests
Sample type
Prolongs PT and APTT
EDTA plasma
Serum/ clotted sample
Under filled primary citrate tube
Heparin contamination
Prolonged or shortened PT, APTT
Partially clotted
Adapted from Favoloro et al, Lab Medicine, 2012; 43
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