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) |
| Normal | 0.0% | 1.% |
| 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 November 26, 2020.« Back to ISTH 2020 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/an-international-study-on-the-interpretation-of-test-results-of-the-aptt-mixing-test/