Final QuickVet Multicenter Report 290610-final - smb.dk 11 - Final...QuickVet values to the results...
Transcript of Final QuickVet Multicenter Report 290610-final - smb.dk 11 - Final...QuickVet values to the results...
Confidential Page 1 BWI 29-06-2010
FACULTY OF LIFE SCIENCES
UNIVERSITY OF COPENHAGEN
BO WIINBERG, DVM, PHD
Assistant Professor
Internal Medicine & ECC
DEPARTMENT OF SMALL ANIMAL
CLINICAL SCIENCES
DYRLÆGEVEJ 16
1870 FREDERIKSBERG C
TELEPHONE 3528 2930
DIRECT 3533 2924
FAX 3528 2929
WWW.DYREHOSPITALET.KU.DK
REF: SMB
BEDES OPLYST VED HENV.
Frederiksberg, June 29th
2010
Final internal report on results of a clinical multicenter
performance study of the QuickVet/Vspro 10LM
PI LIFE: Bo Wiinberg
CI KU: Annemarie T Kristensen, Anette Urbrand Martinsen
PI SMB: Niels Kristian Bau Madsen
CI SMB: Ole Kring
This report is a summary of the results from a data analysis of samples collected in a clinical
multicenter study on the performance of the QuickVet/VSpro 10LM combo coagulation
catridge.
Aims of the study The study was carried out in an effort to evaluate the clinical performance of the Quick-
Vet/VSpro 10LM system. The study has included:
• Correlation to current gold standard in veterinary coagulation testing (ACL TOP 500)
• Establishment of sensitivity and specificity of the system in relation to clinical signs
of systemic coagulopathy at various cut-off points (ROC curve analyses)
• Intra-assay and inter-assay analytical variation
• Determination of guideline reference values
Materials and Methods The study has primarily been carried out at the following locations:
• Department of Small Animal Clinical Sciences, Faculty of Life Sciences, University of
Copenhagen, Frederiksberg, Denmark
• Department of Clinical Sciences, Cummings Scholl of Veterinary Medicine, Tufts Uni-
versity, North Grafton, Massachusetts, USA
• Regions Djursjukhuset Helsingborg, Helsingborg, Sweden
Clinically relevant citrated blood samples were collected from dogs and cats at the clinicians’
discretion. One blood sample was used for duplicate QuickVet/VSpro analyses and the other
spun down and plasma stored for PT and aPTT analyses in Copenhagen. At the initiation of
the study it was planned to include 100 samples from each species.
The analyses are based on samples collected from 165 sick dogs and 35 sick cats. 51 dog
samples and 7 cat samples were excluded from the final data analyses due to lack of docu-
mentation, protocol not adhered to, but the majority due to a cartridge production error.
Positive predictive value, negative predictive value, sensitivity and specificity and cut-off for
optimal detection have been calculated based on clinical data.
Samples from 25 healthy dogs and 13 cats have been used to establish guideline reference
values. We recommend that data from at least healthy 40 dogs and cats is collected in order
to establish a more robust reference range.
GraphPad Prism 5.0 and MedCalc were used for statistical analyses.
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Performance –Agreement
Correlation Analyses Dog
The analyses are based on samples collected from 165 sick dogs. As for correlation of the
QuickVet/VSpro values to the results on the ACL TOP for dogs, the study indicates that there
is a an acceptable correlation for PT (Pearson correlation = 0,72 and Spearman = 0,47) and
slightly better for aPTT (Pearson correlation = 0,93 and Spearman correlation = 0,59). The
Spearman correlation is more precise for small sample sizes of data that is not normally dis-
tributed. A D'Agostino & Pearson omnibus normality test has shown that the data is not nor-
mally distributed and therefore the Spearman test is most precise.
ACL TOP
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Comments Correlation Plots for Canine PT and aPTT:
It is evident from the scatterplot (Dog aPTT QuickVet/VSpro new algorithm) that 10 dogs had
prolonged aPTT on the ACL TOP, but normal aPTT on the QuickVet/VSpro system. The dogs
are indicated on the scatterplot with a blue broken line.
From a review of the patient files it is evident that most of these dogs had either a systemic
disease with a systemic inflammatory response (gastroenteritis, poisoning, acute renal failure
etc.) or they had intracavitary bleeding (thorax/abdomen /pericardium) due to tumour rup-
ture.
There is no obvious common denominator in the files of these dogs, which could explain why
they had prolonged aPTT on the ACL TOP, but normal aPTT on the QuickVet/VSpro system.
With regard to the dogs with a systemic inflammatory response, it is well known that such
patients can have prolonged aPTT without having a systemic coagulopathy. The prolonged
aPTT in these cases are often caused by the inflammatory response.
With regard to the dogs with neoplasia and intracavitary bleeding, there are several likely
explanations for the prolonged aPTT on the ACL TOP:
1. These dogs all had a localized mechanic bleeding that was so severe, that it could
cause a minor systemic coagulopathy, which was detected by the ACL TOP, but not
the QV system.
2. Dogs with severe hemoabdomen often receive large amounts of fluids during the ini-
tial resuscitation. Such therapy could have a transient effect on the clotting times,
wich the ACL TOP is sensitive enough to pick up.
3. Another common denominator for these cases is that they all had neoplasia and
therefore likely a systemic inflammatory response, which may be the cause of the
prolonged aPTT.
A common feature for all the dogs aPTT on the ACL TOP, but normal aPTT on the Quick-
Vet/VSpro system is that they were all suffering from diseases that could predispose to de-
velopment of disseminated intravascular coagulation DIC. These dogs could therefore be in
an early state of DIC. However such patients usually have concomitant prolongation of PT,
low platelet count and high d-dimers and there is not enough data to support that these dogs
were all suffering from DIC.
Correlation to Bleeding - a Clinical Example Though the data analyses shows that there is not a perfect correlation between the two sys-
tems for dogs and cats in the normal and slightly elevated range, the results from a dog with
severe coagulopathy correlate very well with the clinical signs and effect of therapy.
The highest measurements recorded are pre- and post transfusion from a dog that had in-
gested rat poison. The dog bled pre transfusion, but not post transfusion. The results from
this dog indicate that both the aPTT and PT tests are sensitive towards detection of severe
coagulopathy secondary to vitamin K antagonist ingestion, with a PT of 27 seconds (with the
new algorithm, failure with the old algorithm) and aPTT 250 seconds. The tests also show that
PT normalized to 16 seconds post transfusion while aPTT was 116 seconds after transfusion.
These findings correlate well with what was found on the ACL TOP 500.
Data from dog with coagulopathy secondary to ingestion of rat poison
Pre transfusion Post transfusion
PT QV (<17sec) 27 sec 16 sec
PT TOP (<8,5 sec) Out of range 8,2 sec
aPTT QV (<106 sec) 252 sec 116,8 sec
aPTT TOP (<12,5 sec) 160 sec 18,5 sec
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Correlation Analyses Cat
The analyses are based on samples collected from 35 sick cats. As for correlation of the
QuickVet values to the results on the ACL TOP for cats, the study indicates that there is a an
acceptable correlation for PT (Pearson correlation = 0,47 and Spearman = 0,41) and much
better for aPTT (Pearson correlation = 0,76 and Spearman correlation = 0,82). The Spearman
correlation is more precise for small sample sizes of data that is not normally distributed. A
D'Agostino & Pearson omnibus normality test has shown that the data is not normally dis-
tributed and therefore the Spearman test is most precise.
ACL TOP
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Analytical Performance The analytical performance of the assays has been evaluated by performing duplicate meas-
urements on samples from 25 healthy dogs and 13 cats. Coefficients of Variation (CVs) were
determined using the arithmetic mean and variance estimate, based on the difference be-
tween the duplicate samples.
The analytical variation (CVa) of the assays on dog are:
P T N E W
A L G O R I T H M P T O L D
A L G O R I T H M A P T T N E W
A L G O R I T H M A P T T O L D
A L G O R I T H M
I N T R A I N T R A I N T R A I N T R A
1 , 2 % 2 , 2 % 2 , 8 % 2 , 6 %
For comparison, the imprecision data (Intra-assay CVs) for the ACL TOP PT and aPTT are ap-
proximately:
Comment: it is evident that the repeatability performance of the QuickVet is excellent and
room for improvement is therefore very limited. The CV’s for cat are comparable (3,4% for
PT and 3,8% for aPTT). The no clot and error 8 problems which were seen with the previous
algorithm (old) have not been an issue with the new software.
Guideline reference ranges Samples from clinically 25 healthy dogs and 13 cats have been used to establish guideline
reference values. We recommend that data from at least healthy 40 dogs and cats is collected
in order to establish a more robust reference range.
Based on the limited data the range of measurements (minimum-maximum) will most likely
give a reference range closest to the truth (highlight in green below). Alternatively the refer-
ence range can be based on statistical propability indicated by the 95% and 99% CI below,
however the limited amount of data gives a high standard deviation, which causes the refer-
ence ranges to be quiet broad if calculated this way.
P T A P T T
I N T R A I N T R A
1 , 6 % 3 , 2 %
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Setting the Optimum Cut-off for Detection of Systemic Coagulopathy with
Clinical Signs
In order to establish optimum cut-off values and the effect these will have on sensitivity and
specificity for detection of systemic coagulopathy, ROC curve analyses have been performed.
These analyses indicate that placing the cut-off values at the upper end of the reference
range will make both the PT and the aPTT assays very specific and less sensitive.
In a specialised lab, such as the one at the Department of Small Animal Clinical Sciences, LIFE,
KU, we have set up our assays so that they are very sensitive, which gives a number of false
positives. However our assays are used as screening assays and we have other assays such as
thromboelastography to confirm coagulopathy in patients with a slightly prolonged PT or
aPTT.
Based on the ROC curves on the following pages and the results from clinically healthy cats
and dogs we recommend that the upper end of the reference value be placed around:
PT dog < 18 sec
PT cat < 18 sec
aPTT dog < 106 sec
aPTT cat < 120 sec
ROC Curve Analyses Explanations:
-PV = Negative predictive value
+PV = Positive predictive value
-LR = Negative likelihood ratio
-+LR = Positive likelihood ratio
Red asterix signifies highest combined sensitivity and specificity
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Conclusion
The aPTT and PT QV/VsPro 10LM assays are performing well compared to the comparable
ACL TOP assays under these clinical conditions. The LM10 system has impressive repeatability
and good usability, with acceptable agreement to the ACL TOP system. Agree-
ment/correlation analyses do not reveal how the QuickVet system performs with regard to
detection of bleeding or risk of bleeding and therefore is of limited value.
Therefore the 10 LM assays have also been analysed for correlation to clinical signs in order
to establish optimal cut-off values for detection of systemic coagulopathy (ROC Curve Analy-
ses). It must be stressed that several studies have shown that the PT and aPTT assays do not
always perform well in this regard and it is our recommendation that samples from dogs with
clinical signs of systemic coagulopathy are continually collected, in order to improve the data
quality. Knock out studies can likely be performed to determine how the system performs on
samples with single factor (FVII, FVIII and FIX) deficiencies.
Guideline reference ranges have been established in this study. A stronger guideline refer-
ence interval than the one which has been established at this point will require 40-50 dogs
and cats, however true reference ranges will require at least 200 dogs and cats.
Though the performance does not equal that of the the ACL TOP 500, , it is our opinion that
the QV/VsPro 10LM system performs well as a simple patient near PT and aPTT test. The
machine is easy to operate, the tests are easy to run and the results easy to interpret.
Both the PT and aPTT assay have a high specificity with regard to detection of marked sys-
temic coagulopathy. Although these are opposite characteristics compared to most plasma
based assays, which have a high sensitivity, we are of the opinion that the high specificity
should be viewed as a positive attribute in a primary practice setting.
A high specificity will ensure that there are few false positives and also that those animals
which have a prolonged PT/aPTT on the QV/VsPro system have a clinically significant coagu-
lopathy. In other words, the tests can be used to confirm that clinical signs of bleeding are
due to a marked systemic coagulopathy..
Sincerely
Bo Wiinberg & Annemarie T. Kristensen