EN 421 covers two quite different risks that are often confused. Ionizing radiation is energy that passes through material; radioactive contamination is physical particles that can land on the hand.
Protection against radiation
Such a glove contains lead or a lead-equivalent material and must be marked with its lead equivalence in millimetres (0.25 mm Pb, for example). It is used in radiology, nuclear medicine and industrial radiography.
Protection against contamination
Here lead is not needed — leak-tightness is. The glove is tested with the EN 374 air-leak method and often for abrasion resistance too, since a single small hole is enough to let contamination through.
Nuclear facilities often use glove-box gloves built into the working enclosure. EN 421 applies to those too, with additional requirements on puncture resistance and resistance to cracking.