This study is about a condition called cold agglutinin disease (CAD) or cold agglutinin syndrome (CAS). These are health problems where the body’s immune system attacks its own red blood cells. The study is collecting information from patients who have these conditions. It is a real world evidence registry, which means it looks at how things work in everyday life, not just in a lab. The study will follow patients over time to gather data. Some patients may be treated with a medicine called sutimlimab. You can join if you are 18 years or older and have CAD or CAS. You can't join if you have other similar blood diseases or are in another active study for CAD or CAS.

• This is an observational study, meaning no new treatments will be given.
• Participation involves providing health information over time.
• Patients may have been in previous sutimlimab trials.