From Alan Neal, Pathlab, New Zealand: We don’t reflex mixing studies unless clinically directed as they need a responsible clinician to discuss with haematologists. I strongly believe mixing studies can be misleading and numerous studies have identified lupus-like anticoagulants (LLACs, LACs) that correct with APTT mix study; approx. 40% abnormal APTTs do not have an explainable cause. Strategies to use alternate APTT reagent would seem to be more productive.
Thank you for this comment, Dr. Neal, and yes, it is important to select a PTT reagent with low or intermediate LAC responsiveness for coagulopathy screening and heparin monitoring, a choice we recommend to laboratory directors in Fritsma GA, Dembitzer F, Randhawa A, Marques MB, Van Cott EM, Adcock-Funk D, Peerschke EI. Recommendations for appropriate partial thromboplastin time reagent selection and utilization. Am J Clin Pathol 2012; 137: 904–8. LAC-responsive reagent results are most effective in the presence of a clinical indication. Geo.