What this workup supports, and what it does not

This guided case supports a specific, bounded conclusion: given a clean specimen and drug review, an immediate 1:1 mix that falls inside the reference interval and an incubated mix that becomes prolonged describe a time-dependent inhibitory pattern. That pattern is consistent with the FVIII-inhibitor behavior described for acquired hemophilia A, but the mixing study alone does not establish or exclude that diagnosis; FVIII activity and a Nijmegen-modified Bethesda assay are the tests that carry that determination forward.

What this workup does not support is a universal cutoff. The Rosner index, percent correction, and visual correction are all interpretation aids, and a multicenter field study found no single method that reliably separated deficiency from inhibitor across every reagent and site; percent correction did well for PT while aPTT needed method-specific confirmation. The 25.0 to 35.0 second reference interval and the 12.0% Rosner-index limit are local values, not values to carry into a real report without local verification.

This also is not the whole LA workup. LA testing depends on clot-based, phospholipid-dependent assays, and a mix by itself does not confirm LA; a full LA evaluation uses screen, mix, and confirm information from two assay principles, typically a diluted Russell viper venom time and a sensitive aPTT-based system. A weak LA can be diluted enough by 1:1 NPP addition to appear corrected, so a corrected mix does not fully exclude it. None of that changes based on this guided case, because this case's history was negative for anticoagulant exposure and the pattern read was time-dependent, not immediate noncorrection.

The pattern classification and the bounded follow-up recommendation are this workup's output; the diagnosis belongs to the confirmatory tests and the pathologist reviewing them.