Working the guided case

A citrated, platelet-poor plasma specimen was collected at 09:10 with no clot or hemolysis flag, and residual platelet count was below the local limit. Medication review before release showed no anticoagulant reported. PT was 11.8 seconds against a 10.5 to 13.5 second range, unremarkable, which lowers concern for a broad factor deficiency.

The routine aPTT was 48.2 seconds against a 25.0 to 35.0 second range, prolonged. The dRVVT screen was 62.0 seconds against a 30.0 to 44.0 second range, also prolonged. The dRVVT confirm, using the high-phospholipid reagent, shortened to 38.0 seconds, within its own 29.0 to 38.0 second range. The resulting dRVVT normalized screen-to-confirm ratio was 1.42, above the local positive cutoff of greater than 1.20. The silica-based system showed the same pattern: a normalized screen-to-confirm ratio of 1.28, above its local positive cutoff of greater than 1.16.

The dRVVT 1:1 mix screen was 52.0 seconds, above the local mix cutoff of 45.0 seconds, so the mix did not fully correct. That supports an inhibitor, but a weak inhibitor can dilute out in a mix, so this step is read alongside the confirm ratio rather than in isolation. CRP and factor VIII were not available for this specimen, so an acute-phase contribution cannot be assessed and that gap belongs in the report as a stated limitation, not a silent assumption.

Both assay systems show an abnormal screen and an abnormal, disproportionate confirm ratio, which is consistent with phospholipid dependence. With no known anticoagulant and adequate specimen preparation, a defensible release states: results support a phospholipid-dependent inhibitor pattern consistent with lupus anticoagulant by dRVVT and silica clotting time systems; this laboratory result does not diagnose APS; correlate with anticoagulant exposure and clinical context; persistence, when required for classification, is assessed on a subsequent specimen at least 12 weeks later.

Two concordant assay systems, an addressed confounder list, and explicit limitation language make this result defensible to release; a single system or an unaddressed confounder would not.