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Evaluation of International Council for Standardization in Haematology Recommendations on Activated Partial
Shapla Kamali1,2, Minal Dave2, Priyanka Raheja3
1Department of Haematology, Newham University Hospital, Barts Health NHS Trust, London, UK.
Introduction:
Plasma mixing tests are frequently performed in haemostasis laboratories to aid in the determination of the cause of prothrombin time or activated partial thromboplastin time (APTT) prolongation. The International Council for Standardization in Haematology (ICSH) has recently published recommendations for performing and interpreting mixing test; we evaluated the ICSH recommendations for APTT mixing tests on patient samples using automated mixing on a Sysmex CN-series analyser.
Methods:
Samples from patients with haemophilia A with and without inhibitors, or patients with positive lupus anticoagulant, or patients on rivaroxaban/edoxaban, with an APTT ≥ 4 s above normal, were tested using five different APTT reagents: Siemens Actin FS, Actin FSL, and Pathromtin SL; and Hyphen Biomed Cephen and Cephen-LS.
Results:
A likely/possible inhibitor was erroneously diagnosed in all haemophilia patients when assessed using the ICSH criteria, except with Actin FS (erroneous diagnosis in 95%). Using CN-series parameters with locally-derived reference ranges, ≤ 15% of haemophilia patients were erroneously diagnosed. Only Cephen-LS reliably detected lupus anticoagulant by any algorithm.
Conclusions:
When using lupus-insensitive reagents, APTT-mixing tests are of limited value in discriminating between factor deficiencies, lupus anticoagulants, or inhibitors. Incubated mixing tests are essential when diagnosing a FVIII-inhibitor. Rather than perform mixing tests, it is better to be guided by clinical presentation and perform further investigations as appropriate, including analysis of anti-Xa activity for the presence of a direct factor-Xa inhibiting anticoagulant, factor assays in patients with bleeding (or with suspected acquired haemophilia A), and lupus anticoagulant assays in patients with no bleeding.
Frequently Asked Questions
These tests combine patient plasma with normal plasma to see if clotting time corrects. According to the study, failure to correct suggests an inhibitor like lupus anticoagulant or a Factor VIII (FVIII) inhibitor, while correction typically indicates a simple deficiency in coagulation factors.
The study found that ICSH criteria caused an erroneous inhibitor diagnosis in 100% of haemophilia A patients across most reagents. Only the Actin FS reagent performed slightly better, though it still resulted in a 95% misdiagnosis rate for these factor-deficient individuals.
The researchers used the Sysmex CN-series to assess automated mixing parameters and locally-derived reference ranges. This platform allowed them to show that local calibration could reduce erroneous inhibitor diagnoses in haemophilia patients from 100% down to 15% or less.
The authors found that lupus-insensitive reagents have limited value in discriminating between factor deficiencies and inhibitors. Specifically, only the Cephen-LS reagent reliably detected lupus anticoagulant, suggesting that reagent choice is a decisive boundary for the effectiveness of the ICSH mixing algorithms.
The study's authors propose that clinicians should be guided by clinical presentation. They recommend performing anti-Xa activity analysis for direct factor-Xa inhibitors, factor assays for bleeding patients, and specific lupus anticoagulant assays for those without bleeding symptoms to ensure diagnostic precision.
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