Figure 2From: Prospective observational evaluation of the particle immunofiltration anti-platelet factor 4 rapid assay in MICU patients with thrombocytopeniaComparison of PIFA results (positive and negative) with the Gen-Probe PF4 optical density. An optical density of 0.40 or greater is considered a positive result. PIFA, Particle Immunofiltration Anti-Platelet Factor 4 Rapid Assay.Back to article page