Coagulation and Transfusion Medicine / APTT REPORTING IN CANADIAN MEDICAL LABORATORIES
A Survey of aPTT Reporting in Canadian Medical
Laboratories
The Need for Increased Standardization
Malcolm L. Brigden, MD, FRCPC, FACP,1 and Marilyn Johnston, ART2 for the Thrombosis
Interest Group of Canada*
Key Words: aPTT testing; Coagulation testing; Quality assurance
Abstract
A survey of all licensed medical laboratories
performing activated partial thromboplastin time
(aPTT) testing in Canada was undertaken; the response
rate was 50.7%. Preanalytic phase of testing seemed
generally satisfactory, although 46% of laboratories
were still using 3.8% or a 129-mmol/L concentration of
citrate, and only 59% of institutions routinely
performed testing to verify the platelet-poor status of
the plasma used for aPTT testing. There were also
concerns relating to the speed and duration of
centrifugation for specimen preparation. While more
than 67% of institutions had established an individual
therapeutic range for aPTT testing, only 47% of
laboratories verified this range with heparinized
samples. Approximately 67% of the institutions that
had verified the range had done this by spiking
heparin concentrations into pooled plasma rather
than using ex vivo specimens from patients receiving
heparin therapy. There seemed to be a need for
increased education about circumstances under which
the therapeutic range should be rechecked and current
standards for screening for the lupus anticoagulant.
More than 71% of Canadian institutions surveyed
used low-molecular-weight heparin, which may
obviate many of the issues surrounding aPTT testing.
Overall performance as documented by survey results
seemed similar to that reported for the United States
and Australasia.
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Am J Clin Pathol 2000;114:276-282
The laboratory monitoring of heparin therapy constitutes
one of the most common coagulation tests performed, especially by laboratories serving hospitals. 1,2 Despite the
increasing use of low-molecular-weight heparin (LMWH),
which often is not monitored, intravenous unfractionated
heparin still is used for the majority of inpatient clinical
settings. 3 The monitoring of unfractionated therapeutic
heparin is most commonly performed by the activated partial
thromboplastin time (aPTT), with only a few laboratories
routinely assaying heparin levels or using the thrombin clotting time.2,4 Despite common use of the aPTT, considerable
literature suggests problems with reagent instrument variability in the response of the aPTT to heparin. Assay responsiveness is influenced further depending on whether heparin
is added in vitro or assayed in samples from patients
receiving heparin when the therapeutic range is being established. Both the American College of Chest Physicians and
the College of American Pathologists have provided recommendations about heparin therapy.5,6 Currently, it is recommended that each laboratory establish an individual therapeutic range for heparin specific to its own reagent and
instrument system.7-9 To assess methods of standardization,
reporting, and general knowledge relating to aPTT testing,
the Thrombosis Interest Group of Canada, a cohort of health
professionals with a major interest in thrombosis, undertook a
national survey of Canadian laboratories performing aPTT
testing from January 1998 through March 1999. The principal reason for this study was to obtain information on the
preanalytic phase of specimen preparation, how testing was
performed, how laboratories verified aPTT therapeutic
ranges, and other related questions.
© American Society of Clinical Pathologists
Coagulation and Transfusion Medicine / ORIGINAL ARTICLE
Materials and Methods
All registered clinical laboratories in Canada that
perform coagulation testing, including hospitals and outpatient facilities, were identified by provincial licensing agencies. In late 1998, a standardized questionnaire was sent to
the laboratory cohort. Laboratories were asked about the
type of instrumentation and reagents used, the volume of
testing performed, the procedures used for the preanalytic
phase of specimen preparation, quality assurance procedures
used, and a variety of issues relating to the establishment of
therapeutic ranges and result reporting ❚Appendix 1❚.
Results
As in the United States, there has been a systematic
consolidation of medical services such that the number of
laboratories actually performing coagulation testing
continues to diminish. In all, 329 responses were received
from 649 known laboratories, an overall response rate of
50.7%. Single hospital laboratories constituted the largest
group at 156 (47.4%), followed by community outpatient
laboratories (104 [31.6%]) and regional laboratories (43
[13.1%]), with 26 (8.0%) encompassing a variety of categories. In keeping with an increasing trend to centralization,
30% of responding institutions had both a central core laboratory and a rapid response stat laboratory. The average
number of aPTT tests performed per laboratory per week
varied from fewer than 10 to more than 1,400 (median, 1020 tests per laboratory per week).
Of the institutions, 47% reported using different instruments and reagents for aPTT testing within their various
facilities. Three manufacturers—Organon Teknika
(Durham, NC), Instrumentation Laboratories (IL,
Lexington, MA), and Hemoliance (MLA, Pleasantville,
NY)—accounted for the majority of analyzers used. As a
result of a recent merger, Instrumentation Laboratories and
Hemoliance have been consolidated with Beckman Coulter
(Miami, FL). Of interest was the fact that for primary
analyzers, the age of machines varied from new to older
than 10 years (median age, 5 years).
The survey indicated that 2 manufacturers—Organon
Teknika and Instrumentation Laboratories (Beckman/
Coulter)—accounted for the majority of the reagents used
❚Figure 1❚.
In relation to the preanalytic phase of aPTT testing, 54%
of laboratories used 3.2% or a 105-mmol/L concentration of
citrate concentration for specimen collection, while 46%
used 3.8% or a 129-mmol/L concentration. The time that
various laboratories allowed between specimen collection
and performance of the aPTT was 4 hours or less in 90% of
cases, but more than 4 hours in 10% of institutions. Of the
© American Society of Clinical Pathologists
institutions responding, 93% had their centrifuges calibrated,
most commonly by tachometer and stopwatch. It was noteworthy that 7% of laboratories had never calibrated their
centrifuge. Of the responding institutions, 95% verified the
centrifuge calibration on a regular basis (median time, 1
year). The centrifugation times used by various laboratories
to prepare plasma for aPTT testing are graphed ❚Figure 2❚.
Interestingly, 1 institution had no maximum time interval
defined, and another had no policy in this regard. The speed
of centrifugation varied from 1,000 to 8,500 rpm (median,
3,000 rpm). Only 59% of institutions performed testing to
verify the platelet-poor status of the plasma used for aPTT
testing. Most commonly, verification consisted of platelet
counts performed on a regular basis varying from once
weekly to once monthly.
The survey of the analytic phase of aPTT testing showed
that the median length of a working shift was 8 hours and
that the median number of controls run per shift was 3
(range, 1 to >10). One hundred percent of laboratories used a
normal control, 97% used a high control, and 65% used a
low control. Of the laboratories responding, 71% did not run
controls in duplicate, while 29% did; 71% of laboratories
also did not run specimens in duplicate, whereas 29% did.
Of the responding laboratories, 53% reestablished the reference range with each new lot of thromboplastin, while 47%
did not.
An individual therapeutic range was established by 66%
of institutions but not by 34%. The most common therapeutic ranges reported by responding laboratories are shown
in ❚Figure 3❚. Heparinized samples were used by 57% of
institutions to verify their therapeutic range. Of institutions
that had verified their therapeutic range, 67% had done this
by spiking heparin concentrations into normal pooled
plasma, while 33% had used ex vivo specimens from
patients receiving heparin therapy. In institutions where
heparin levels had been measured, 90% had performed this
by anti-factor Xa chromogenic assay, whereas 10% had used
the protamine titration assay.
Indications reported for reassessment of the aPTT therapeutic range are illustrated in ❚Figure 4❚. The therapeutic
range would be rechecked after a change in instrument or
reagent by 61% and 60% of laboratories, respectively,
whereas only 42% would recheck after a change in reagent
lot number.
In relation to aPTT reporting, almost 100% of laboratories supplied the aPTT in seconds with only 1 institution
reporting the aPTT as a ratio. Of the responding institutions,
51% provided the therapeutic range to physicians with individual aPTT results. Absolute aPTT values were reported by
33%, while 67% reported values up to a finite number. In this
regard, 150 seconds was the median value beyond which these
institutions did not supply a numeric result. Supratherapeutic
Am J Clin Pathol 2000;114:276-282
277
Brigden et al / APTT REPORTING IN CANADIAN MEDICAL LABORATORIES
50
70
40
38%
35
30
27%
25
20
16%
15
12%
10
7%
Percentage of Laboratories
Percentage of Laboratories
45
60
50%
50
39%
40
30
20
5
10
0
0
8%
3%
IL (Beckman
Coulter)
Organon
Teknika
Hemoliance
(Beckman
Coulter)
Dade
Behring
2-5
Other
6-9
10-14
15 or more
Minutes
❚Figure 1❚ Activated partial thromboplastin time reagents in
use in hematology laboratories in Canada. Beckman Coulter,
Miami, FL; Organon Teknika, Durham, NC; Dade Behring,
Deerfield, IL.
❚Figure 2❚ Duration of centrifugation used for the preparation of platelet-poor plasma for activated partial thromboplastin time testing in hematology laboratories in Canada.
50
45
70
Percentage of Laboratories
Percentage of Laboratories
40
35
32%
30
25
20
15
12%
10
13%
11%
12%
61%
60
60%
50
42%
40
34%
30
20
10
8%
7%
5%
5
0
No
Policy
0
40-85
50-85
50-100 55-90
60-85
60-90 60-100
Change in
Instrument
Change in
Reagent
Change in
Reagent Lot
>60
Seconds
❚Figure 3❚ Specific therapeutic ranges for activated partial
thromboplastin time in hematology laboratories in Canada.
❚Figure 4❚ Indications for the reevaluation of the therapeutic
range for activated partial thromboplastin time testing in
hematology laboratories in Canada.
levels were telephoned by 83% of institutions; the most
common aPTT panic value for telephoning was more than
100 seconds. Subtherapeutic values were highlighted by
45% of laboratories but not by 55%.
Of the 329 laboratories, 112 (34.0%) performed some
type of lupus anticoagulant testing ❚Table 1❚. An isolated
elevation of the aPTT with a mixing study was not followed
up in patients not receiving heparin in 58% of institutions;
19% of laboratories routinely followed up, while 23% did so
in selected cases. The sensitivity of the aPTT reagent for
screening for the lupus anticoagulant had not been verified
by 83% of institutions, while in 17%, verification had been
performed. A specific lupus-sensitive aPTT reagent was used
by 31% of laboratories when lupus anticoagulant testing was
ordered. The dilute Russell viper venom time test was used
by 18% of institutions; most commonly a commercial
reagent was used. Other tests were performed by 82% of
institutions as part of the routine study for the presence of a
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Am J Clin Pathol 2000;114:276-282
© American Society of Clinical Pathologists
Coagulation and Transfusion Medicine / ORIGINAL ARTICLE
❚Table 1❚
Practices of 112 Laboratories for Performing Lupus Anticoagulant Testing
Practice
Verification of sensitivity of aPTT reagent for lupus anticoagulant testing
Use of a specific lupus anticoagulant–sensitive reagent
Use of DRVVT test
With an abnormal aPTT detected
Performance of 50:50 mixing study
Performance of other secondary testing
Performance of anticardiolipin antibody testing
Routinely
Only if requested
Percentage of Laboratories Performing
17
31
18
42
18
19
81
aPTT, activated partial thromboplastin time; DRVVT, dilute Russell viper venom time.
lupus anticoagulant. Most commonly, this involved some
form of phospholipid neutralization. In 50% of cases, this
was performed using high phospholipid in the dilute Russell
viper venom time test as confirmation. In 30% of cases, the
platelet neutralization procedure was used, while in 20%,
hexagonal phase phospholipid neutralization was used. The
majority of laboratories (81%) would only perform anticardiolipin antibody testing if specifically requested.
Of the responding institutions, 71% reported the use of
LMWH therapy. Some form of monitoring for LMWH
therapy was used by 25% of laboratories. In 71% of cases,
monitoring was by anti-factor Xa chromogenic assay, while
in 29% of cases, it was by an anti-Xa clotting assay.
Discussion
The aPTT remains the most commonly used test for
monitoring unfractionated intravenous heparin therapy.1-3
Many reagent instrument systems are available to perform
the aPTT. However, our study showed that 3 suppliers of
both reagents and instruments dominate the Canadian
market. Of interest was the fact that the median age of
existing analyzers was 5 years, suggesting that laboratories
are not in a rush to obtain new instrumentation in view of the
increasing use of LMWH. The most frequent volume of
testing was 10 to 20 specimens per week despite the fact that
hospitals constituted the majority of responding institutions.
With regard to preanalytic variables related to aPTT
testing, current National Committee for Clinical Laboratory
Standards (NCCLS) recommendations are that plasma for
coagulation testing be prepared by centrifugation at 1,500g for
15 minutes; however, these guidelines are under review.10
Inadequately centrifuged samples can leave residual platelets
that may release platelet factor 4, which will neutralize heparin
in the sample. This could result in falsely low aPTT values.1,4
In addition, if plasma samples are frozen, residual platelets can
alter the detection of the lupus anticoagulant.11,12 For this
reason, it is imperative that each laboratory assess the
© American Society of Clinical Pathologists
centrifuges used for specimen preparation to determine the
rpm needed to produce an adequate centrifugal force. The
relationship between relative centrifugal force and rpm is
expressed by the formula RCF = 111.8 × 10–7 × r × N2, where
r is the radius of the centrifuge head in centimeters and N is
the speed of rotation in rpm.10 In our study, the most common
reported speed of centrifugation was 3,000 rpm, and the most
frequent range of centrifugation was 10 to 14 minutes.
Without knowing the specific centrifuge used, however, it is
not possible to determine the centrifugal force used by individual laboratories. However, a similar study in Ontario found
that 40% of responding laboratories used centrifugal forces of
less than 1,500g. It also is of concern that only 31% of laboratories centrifuged their specimens for 15 or more minutes to
prepare platelet-poor plasma. Yearly calibration of centrifuges
usually represents a requirement for diagnostic certification in
Canada. Thus, it was surprising that 7% of institutions
reported having no policy in this regard.
In relation to the duration of time between specimen
collection and performance of the aPTT for patients treated
with unfractionated heparin, NCCLS guidelines state that
samples can be assayed up to 4 hours after phlebotomy if
centrifuged within 1 hour of collection.10 The guidelines do
not stipulate whether samples should be stored as whole
blood or require centrifugation before storage. Some studies
have found up to a 25% decrease in the aPTT over 2 hours
for uncentrifuged specimens obtained from patients
receiving heparin therapy when the specimens were kept at
room temperature, and there have been further decreases for
up to 24 hours.13 In these studies, iced samples kept at 4°C
were stable. Such a significant ex vivo decrease in aPTT
values over time with whole blood samples kept at room
temperature could result in “overheparinization” of patients
owing to an underestimation of the actual in vivo heparin
effect.13 In this regard, while only 10% of responding laboratories were analyzing specimens beyond the 4-hour time
limit, if other laboratories are maintaining specimens as
uncentrifuged whole blood samples at room temperature for
up to 4 hours, this may still represent a concern.
Am J Clin Pathol 2000;114:276-282
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Brigden et al / APTT REPORTING IN CANADIAN MEDICAL LABORATORIES
In regard to the citrate concentration used for collection
of aPTT specimens, it was interesting that 46% of
responding laboratories were still using 3.8% or a 129mmol/L concentration of citrate. This concentration is not
recommended by the NCCLS. Studies have shown that aPTT
samples drawn into 3.2% or a 105-mmol/L concentration of
sodium citrate better tolerate a less than optimum filled
volume of the aPTT collection tube.14 In addition, since a
higher citrate concentration binds more assay-added calcium
making less available to promote clot formation, the aPTT is
typically longer with 3.8% citrate tubes than 3.2% citrate
tubes.14-16 This may be especially problematic if responsive
aPTT reagents are used. In the United States, it had been
reported that approximately 70% of clinical laboratories still
used 3.8% citrate.14
With regard to the number of controls used, authorities
usually recommend that at least 1 level be run on each
shift.4,17 In the present study, the number of controls run and
the levels used seemed to be appropriate for the majority of
laboratories. Of interest was the fact that more than 70% of
Canadian laboratories no longer seem to be running specimens or controls in duplicate; appropriate policy changes are
well documented in the literature.18 However, it was somewhat disconcerting that only 53% of laboratories would
reestablish a reference range with each new lot of aPTT
reagent, since this usually constitutes a requirement for laboratory recertification.
Because there is wide variation in the heparin sensitivity
of different aPTT reagents and even differences in heparin
sensitivity between individual batches of the same reagent,
current recommendations are that each laboratory standardize an aPTT therapeutic range equivalent to a heparin
activity of approximately 0.3 to 0.7 µ/mL as determined by
an anti-factor Xa assay or to an antithrombin activity range
of 0.2-0.4 U/mL as measured by protamine neutralization.1,7,9 Furthermore, the equivalence should be determined
by using ex vivo plasma samples obtained from patients
treated with unfractionated heparin rather than spiked in
vitro heparinized plasma samples.9,19 A justifiable concern
exists that smaller laboratories processing 10 to 20 aPTT
tests daily might have difficulty obtaining sufficient specimens to establish a therapeutic range.5,6 An alternative
approach would be to work with a larger coagulation laboratory or reference laboratory in which sufficient plasma
samples would be available, and the smaller laboratory’s
reagent could be tested. Manufacturers also should be
encouraged to establish heparinized plasma that would target
the therapeutic reference range for their reagent-instrument
combinations. It is of concern that 34% of Canadian laboratories had no official therapeutic range established for aPTT
determinations, while 53% that reported a therapeutic range
had not verified it. While the majority of laboratories that
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Am J Clin Pathol 2000;114:276-282
had verified their therapeutic range had measured heparin
activity by anti-factor Xa assay rather than protamine
neutralization, 67% had used spiked heparin samples of
normal pooled plasma contrary to current
recommendations.9,19 A similar study performed in the
United States as part of the comprehensive coagulation
survey of The American College of Pathologists in 1995
showed that 23% of laboratories used in vitro heparin
spiking to establish a therapeutic range, while 35% relied on
the medical literature, and 32% had no established therapeutic range.4 Somewhat similar figures have been reported
from Australasia.2
Current consensus exists that therapeutic ranges should
be recalculated after the introduction of a new thromboplastin or a new lot of the same thromboplastin. In the
present study, it was disconcerting to find that approximately 60% of laboratories would reassess the therapeutic
range for a change in instrumentation or reagent and only
40% for a change in reagent lot numbers. In relation to the
reporting of therapeutic ranges, it was notable that significantly more supratherapeutic levels were highlighted than
were subtherapeutic levels, 83% and 45%, respectively.
This is surprising because it has been established that
recurrence rates for venous thrombosis are higher when
subtherapeutic aPTTs persist for more than 48 hours after
initiation of heparin therapy.20
The data relating to the use of the aPTT for the examination of lupus anticoagulants also revealed discrepancies
compared with current recommendations. 11,12,21 Of
responding institutions, 83% had not verified the sensitivity
of their aPTT reagent for screening for a lupus anticoagulant. In addition, more than half of the institutions
responding did not follow up an abnormal result with a
50:50 mixing study with normal pooled platelet-poor
plasma when an elevated aPTT was detected in patients not
receiving heparin therapy.11,21
As a final observation, more than 71% of Canadian
institutions responding are now using LMWH therapy, and
the majority who monitor LMWH activity do so with antifactor Xa chromogenic assays. This increasing use of
LMWH ultimately may obviate many of the questions
surrounding the optimum use of the aPTT and the therapeutic monitoring of heparin therapy. Indeed, the present
time has been referred to in the literature as the “twilight” of
anticoagulant monitoring.3
A survey of laboratories performing aPTT testing in
Canada revealed generally satisfactory methods. In the
preanalytic phase, further education seems to be needed in
relation to the speed and duration of centrifugation and the
appropriate preparation of platelet-poor plasma for aPTT
testing. Other areas requiring remedial action include a need
for standardization of the duration of time between specimen
© American Society of Clinical Pathologists
Coagulation and Transfusion Medicine / ORIGINAL ARTICLE
collection and test performance, the continued use of 3.8%
citrate by a substantial number of laboratories, and the
failure to establish and report a therapeutic range for heparin
therapy. In addition, a number of laboratories with established therapeutic ranges continued to verify the therapeutic
range by spiking various heparin concentrations into normal
pooled plasma as opposed to using ex vivo heparinized
samples, as is currently recommended. There also seemed to
be a need for increased education relating to the circumstances under which the therapeutic range should be
rechecked and current standards for the screening for the
lupus anticoagulant. While overall survey results were as
satisfactory as those that have been reported from the United
States and Australasia, continuing education and as periodic
proficiency surveys are necessary to motivate laboratories to
improve performance in all areas.
From the 1Penticton Cancer Clinic, Penticton Regional Hospital,
Penticton, British Columbia, and the 2Hemostasis Reference
Laboratory, Hamilton Civic Hospitals Research Centre, Hamilton,
Ontario.
Supported in part by a grant from DuPont Pharma, Mississauga, Ontario.
Address reprint requests to Dr Brigden: BC Cancer Agency,
Center for the Southern Interior, 399 Royal Ave, Kelowna, BC,
Canada V1Y 5L3.
* The members of the Thrombosis Interest Group of Canada
are Maureen Andrew, MD; Janis Bormanis, MD; Malcolm
Brigden, MD; Cedric Carter, MD; Moira Cruickshank, MD;
Michele David, MD; Christine Demers, MD; Sean Dolan, MD;
William Geerts, MD; Jeffrey Ginsberg, MD; Jack Hirsh, MD;
Donald Houston, MD; Russell Hull, MD; Judy Johnson, RN;
Marilyn Johnston, RT; David Lee, MD; Michael Mant, MD;
Patti Massicotte, MD; Graham Pineo, MD; Susan Robinson, MD;
H. Elizabeth Ross, MD; Andre Roussin, MD; Sheila RutledgeHarding, MD; Mary-Frances Scully, MD; Susan Solymoss, MD;
A. Graham Turpie, MD; Linda Vickars, MD; and Lucinda
Whitman, MD.
References
1. Brill-Edwards P, Ginsberg J, Johnston M, et al. Establishing a
therapeutic range for heparin therapy. Ann Intern Med.
1993;119:104-109.
2. Mackinlay N, Favaloro E, Arthur C, et al. A survey of heparin
monitoring in Australasia. Pathology. 1996;28:343-347.
3. Hull RD, Pineo GF, Stein P. Heparin and low molecular
weight heparin therapy for venous thromboembolism: the
twilight of anticoagulant monitoring [editorial]. Int Angiol.
1998;17:213-224.
4. College of American Pathologists. Comprehensive Coagulation
Survey. 1995 Set GC2-A. Participant Summary. Northfield,
IL: College of American Pathologists; 1995.
5. Olson JD, Arkin CF, Brandt JT, et al. College of American
Pathologists Conference XXXI on laboratory monitoring of
anticoagulant therapy: laboratory monitoring of
unfractionated heparin. Arch Pathol Lab Med. 1998;122:
782-798.
© American Society of Clinical Pathologists
6. Hirsh J, Warkentin TE, Raschke R, et al. Heparin and lowmolecular-weight heparin: mechanisms of action,
pharmacokinetics, dosing considerations, monitoring, efficacy,
and safety. Chest. 1998;114(5 suppl):489S-510S.
7. Shojania AM, Tetreault J, Turnbull G. The variations
between heparin sensitivity of different lots of activated
partial thromboplastin time reagent produced by the same
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8. Eby C. Standardization of aPTT reagents for heparin therapy
monitoring: urgent or fading priority [editorial]? Clin Chem.
1997;43:1105-1107.
9. Kitchen S, Jennings I, Woods T, et al. Wide variability in the
sensitivity of aPTT reagents for monitoring of heparin dosage.
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10. National Committee for Clinical Laboratory Standards.
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Coagulation Testing and General Performance of Coagulation
Assays. 3rd ed. Approved Guideline. H21-A3. Vol 18; No. 20.
Wayne, PA: National Committee for Clinical Laboratory
Standards; 1998.
11. Triplett D. New diagnostic strategies for lupus anticoagulants
and antiphospholipid antibodies. Haemostasis. 1994;24:
155-164.
12. Brandt J, Triplett D, Rock W, et al. Effect of lupus
anticoagulants on the activated partial thromboplastin time.
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13. Adcock D, Kressin D, Marlar R. The effect of time and
temperature variables on routine coagulation tests. Blood
Coagul Fibrinolysis. 1998;9:463-470.
14. Reneke J, Etzell J, Leslie S, et al. Prolonged prothrombin time
and activated partial thromboplastin time due to underfilled
specimen tubes with 109 mmol/L (3.2%) citrate
anticoagulant. Am J Clin Pathol. 1998;109:754-757.
15. Adcock D, Kressin D, Marlar R. Effect of 3.2% vs 3.8%
sodium citrate concentration on routine coagulation testing.
Am J Clin Pathol. 1997;107:105-110.
16. Adcock D, Kressin D, Marlar R. Minimum specimen volume
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17. Ontario Medical Association. Coagulation Questionnaire K9712: Patterns of Practice in Heparin monitoring. Vol 3.
Toronto, Ontario: Laboratory Proficiency Testing Program,
Ontario Medical Association; April 1998.
18. Ivey L, Thom J, Baker R. Single or duplicate analysis for
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Brigden et al / APTT REPORTING IN CANADIAN MEDICAL LABORATORIES
❚Appendix 1❚❚
Questionnaire for aPTT Reporting Study
1. Lab “Responsibility” or Type
2. Does your city (or group of hospitals) have one central laboratory (core lab) and a rapid response lab (STAT lab) in each facility?
3. A. Primary Instrumentation for aPTT:
B. Secondary Instrumentation If Different:
4. Activated Partial Thromboplastin Reagent
Citrate concentration utilized:
3.2%
3.8%
Is your normal reference range recalculated with each new lot of partial thromboplastin?
Yes
No
5. Preanalytic Phase of aPTT Testing
What is the maximum time your lab allows between specimen collection and performance of the aPTT?
How long do you centrifuge specimens to prepare platelet-poor plasma for the aPTT testing?
What is your speed of centrifugation?
How is your centrifuge calibrated?
How often is your centrifuge calibration verified?
Have you performed any other testing to verify the platelet-poor status of your plasma used for aPTT testing?
6. Method of Operation—Controls Utilized
Levels Used: Normal
High
How many controls are run per shift?
Are controls run in duplicate?
How long is a shift?
Are specimens run in duplicate?
7. Establishment of a Therapeutic Range for Heparin Therapy
Is there an official recommended therapeutic range for heparin therapy in your lab/hospital?
Was the therapeutic range verified?
If YES, how was the therapeutic range verified?
1. By spiking various heparin concentrations into normal pooled plasma
2. By using samples from patients being treated with heparin
If YES to no. 2, how is the heparin assayed?
3. Heparin levels were measured by protamine titration
4. Heparin levels were measured by factor Xa chromogenic assay
8. Under what conditions do you reassess your aPTT therapeutic range?
9. Current Method of aPTT Reporting
aPTT in Seconds:
aPTT Ratio:
10. Reporting Therapeutic Ranges
Do you supply therapeutic ranges to physicians?
Are nontherapeutic levels highlighted?
Are supratherapeutic levels phoned?
What is your “panic level” for phoning elevated aPTTs?
11. aPTT Reagent and the Lupus Anticoagulant
If an elevated aPTT is detected in patients not receiving heparin, is a 50:50 mixing study done?
Have you verified the sensitivity of your aPTT reagent for use in the screening for the presence of a lupus anticoagulant?
Do you use a lupus-sensitive aPTT when lupus anticoagulant testing is ordered?
Do you do the dilute Russell viper venom time test?
If the screening aPTT is normal, do you perform other lupus-sensitive tests for the presence of a lupus anticoagulant?
Under what circumstances are assays for anticardiolipin antibody performed?
12. Phoning of Results
Do you phone all aPTT results?
Yes
No
If NO, do you phone only critical results?
13. Do you report all aPTT values or only values to a certain level?
14. Is your hospital using low-molecular-weight heparin?
If YES, are you monitoring (testing)?
If YES, by what method? Anti Xa clotting
Yes
No
Yes
No
Anti Xa chromogenic
Other (specify)
aPTT, activated partial thromboplastin time.
282
Am J Clin Pathol 2000;114:276-282
© American Society of Clinical Pathologists