Abstract Number: PB0582
Meeting: ISTH 2020 Congress
Background: The APTT mixing test is a useful tool to gain insight in the potential cause of a prolonged APTT. However, it has been demonstrated that, using case scenarios, it can be problematic to correctly interpret APTT mixing test results (Ajzner et al, Clin Chem Lab Med, 2015: 1593-603). Therefore a follow-up study was conducted to investigate the interpretation of APTT mixing test results on the basis of real test results.
Aims: A follow-up study was conducted to investigate the interpretation of APTT mixing test results on the basis of real test results.
Methods: Two lyophilized citrated plasma samples together with case histories were distributed to 340 European laboratories. Laboratories were asked to perform an APTT and mixing test according to their own in-house procedures. The participants were also asked to interpret the obtained test results in the perspective of the provided case history and classify the sample according to the following categories: normal, coagulation factor deficiency, presence of an inhibitor, presence of anticoagulant or unknown. Multiple selections were allowed.
Results: Results of 270 laboratories were evaluated. For case 1 (sample contaminated with heparin), 100% found a prolonged APTT and about 90% a prolonged initial and incubated mixing test result. For case 2 (factor VIII deficiency) almost all participants reported a prolonged APTT result and 78% found a correction to normal in the mixing test. The results of the classification of both samples is given in the table below.
Conclusions: This study demonstrates again that for particular scenarios the interpretation of APTT mixing test results can be problematic.
|Classification||Case 1 (heperin contamination)||Case 2 (factor VIII deficiency)|
|Coagulation Factor Deficiency||4.5%||85.5%|
|Inhibitor (specific or non-specific)||35.1%||3.4%|
|Presence of anticoagulant||14.9%||0.0%|
|Normal / Coagulation Factor Deficiency||0.0%||0.4%|
|Factor Deficiency / Inhibitor||4.1%||1.9%|
|Factor Deficiency / Anticoagulant||3.0%||3.8%|
|Inhibitor / Anticoagulant||33.2%||0.0%|
|Factor Deficiency / Inhibitor / Anticoagulant||3.4%||2.3%|
[The results of the classification of case 1 and 2]
To cite this abstract in AMA style:Meijer P, Bauça JM, Ajzner É, Hillarp A, Kristoffersen AH, Working Group on the Postanalytical Phase (EFLM / EQALM) . An International Study on the Interpretation of Test Results of the APTT Mixing Test [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/an-international-study-on-the-interpretation-of-test-results-of-the-aptt-mixing-test/. Accessed May 15, 2021.
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