Any of a group of disorders marked by hemolytic anemia, obstruction of the microcirculation, or both. It is caused by agglutination of red blood cells by immunoglobulins that precipitate at cool or cold temperatures. The most common symptom is Raynaud’s phenomenon. Cold agglutinin disease often occurs transiently after infection with Mycoplasma pneumoniae or Epstein-Barr virus. Often the cause is idiopathic.