Subvisible particles

Particles in injectable solutions too small to see by eye, roughly 2 to 100 µm across, counted by light obscuration or flow imaging. The pharmacopoeial test for injections, harmonized between USP <788> and its Japanese and European counterparts, sets limits for particles of 10 µm and 25 µm and larger. For protein products, smaller particles are also monitored because they signal aggregation and may affect immunogenicity. The Japanese term is the one used in the JP test title, so a Japanese specification line with this word usually refers to that compendial test.