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| Hemochron ® Signature PT Testimonial Paper |
| 1.
Details |
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Mr
P. Carson, Clinical Scientist, Miss T. Vercoe, Biomedical Scientist,
Haematology Department, Royal Cornwall Hospital, Cornwall, TR1 3LJ,
England. |
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Nurses
at Doctors surgeries perform INR's in clinics using a framework planned
and overseen by hospital laboratory, working in partnership as guidelines
for POCT emphasise (1). |
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| 2.
Hemochron Details |
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12
surgeries using the Hemochron ® Signature. |
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J201C
cuvettes used by surgeries, all using same batch for an extended
time for continuity. |
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Approximately
of 2,000 patients being controlled by surgeries in this way. |
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Estimate
of usage = 24,000 cuvettes per year. |
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| 3.
INR results |
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INR
results entered into surgeries dosage computer |
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Most
surgeries have INR Star system (which was developed by a local GP). |
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Dosage
letter then given to patient before leaving consultation. |
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A
few patients seen at branch surgeries, samples being tested later,
and results posted. |
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| 4.
Quality assessment |
| Framework
for INR testing in Primary Care in Cornwall |
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Initially
the lead GP for anticoagulation contacts the laboratory for a discussion
of the issues involved with INR testing. |
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An
enabling visit then provides the opportunity to review INR testing,
discuss all operational issues with the lead GP and practice nurses. |
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After
purchase of an instrument, a validation process is undertaken, whereby
at least 40 consecutive samples are analysed by both the POCT site
and Laboratory (2). |
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Once
established the ongoing service is operated under a Service Level
Agreement. This is defined for the surgery and covers the operation
of an INR testing service with the following safeguards (3): |
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Only
trained operatives use the instrument. |
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A
manufacturers control is used at the start of every clinic to check
instrument. |
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One
sample from each clinic is sent to the laboratory for duplicate testing. |
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All
INR's > 5 are checked by the laboratory due to the great divergence
of INR's between reagents at this level. |
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| Duplicate
testing scheme in detail |
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Ongoing
assessment is evaluated by sending one sample from each session to
the laboratory for duplicate analysis, with the surgery result, reagent
batch details and the selected patients dosage target range recorded. |
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Details
are entered onto into an Access database and data is examined as
the % difference in the INR's. The latter being presented as a serial
graphical plot. |
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The
overall trend of each POCT site is noted. When a result of >20% difference
initially occurs, multiple samples from the next clinic are requested.
Individual sample differences (citrated plasma v citrated whole blood
or native whole blood) or a potential system error could then be
differentiated. Any continued variance greater than 15% is further
investigated. |
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The
graph is reported by general post to the surgery with any actions
to be taken recorded or the laboratory responds by telephone if immediate
action is required. |
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In
10 years this simultaneous / duplicate venous sample analysis process
has identified labile batches, fridge errors, pipetting issues in
four INR POCT methods (4). |
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| 5.
Signature controls |
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Surgeries
use electronic/temperature check on the instrument at the start of
each day of use to ensure instrument working. |
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Surgeries
are recommended to use Directcheck at least once a week. |
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These measurements are kept as part of an audit trail to enable tracing of
who produced result and to show instrument was in control. |
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| 6.
Proficiency surveys |
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Surgeries
are recommended to participate in the NEQAS Blood coagulation scheme. |
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As
an improvement to the local scheme, we aim to block register all
surgeries, gaining a discount from the organiser and include the
fee to our annual charge. |
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| 7.
Experience with Signature |
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Initial
laboratory evaluation based on 24-sample comparison, suggested an
accurate, reproducible and comparable system. |
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A
full analysis was possible as all surgeries then performed 40 sample
comparisons giving a total of around 300-sample population, this
was investigated as the basis of a MSc project. Plasma was stored
to analyse the sensitivity of the methods to levels of the vitamin
K-dependent clotting factors II, VII, and X and clotting factor V.
The sensitivity of the Hemochron® Signature to the factors was
shown to be closer to the laboratory method than the previous point
of care method. However, interestingly only 3% of the discrepant
results of Hemochron® Jr. to the laboratory method could be explained
by differences in levels of the four clotting factors, indicating
the influence of other variables on INR. The project confirmed the
Hemochron showed satisfactory agreement to the laboratory results
with a high degree in concordance of clinical decisions, and all
surgeries performed satisfactorily. Minimal variation in batch performance
was seen (5). |
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Hemochron
was used successfully for a one-year period with minimal batch variation. |
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To improve continuity a single batch was then arranged for all surgeries for an extended period. Unfortunately it became quickly apparent this batch was of not to the usual high standard and was of borderline release specifications. A high percentage of over 15% difference between laboratory and Hemochron ® Signature INR’s was seen which resulted in the usual 85% dosage agreement falling to 75%. The framework identified this issue within 2 weeks as multiple surgeries demonstrated the pattern. |
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Elitech,
the UK distributor, and ITC responded to the problem immediately
(even though this was 23rd December), after communication a temporary
replacement batch was received within a week. |
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The
surgeries then moved to a new long-term batch within a month, this
has been satisfactory. |
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By
monitoring surgeries for INR testing for 10 years now we have seen,
on occasions, issues with all the systems. The importance to us,
is how the manufacturer responds at these times, Elitech / ITC reacted
appropriately. We are confident we are working in partnership with
them and the surgeries to provide quality INR testing service. |
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| 1. |
Joint
Working Group on Quality Assurance. (2000), Near to Patient or Point
of Care Testing, Clinical Laboratory Haematology, 22, 185-188. |
| 2. |
British
Committee for Standards in Haematology. (1995) Guidelines for Near
Patient Testing: Haematology. Clinical and Laboratory Haematology;
17:301-310. |
| 3. |
Carson
PJ, Blundell J Creagh MD (2000) Implementation and performance improvement
by monitoring of point of care (POCT) for INR's in primary care, British Journal
of Haematology, 108, Suppl 1, p76, Ab 198 |
| 4. |
Carson
PJ, Hicks MK, Creagh MD (2002) Identification of system faults by
monitoring of point of care testing (POCT) for INR'S in Primary Care,
British Journal of Haematology, 117, Suppl 1, 28. |
| 5. |
T
Vercoe, (2005) Continuation of the provision of safe INR testing
in GP surgeries with a detailed investigation of discrepant results,
MSc Dissertation, Anglia University. |
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