Cold agglutinin syndrome secondary to Mycoplasma pneumoniae

A 47-year-old female presented with dyspnea, dry cough, and fatigue for ten days. On examination, she had severe pallor and bilateral crepts in the lungs. Complete blood count (CBC) showed a hemoglobin of 7.3 g/dL, reticulocyte count of 5.6%, and chest X-ray was normal. Her extended Direct Coombs test (DCT) showed C3d +3 and cold agglutinin titer of 1:256 at 4°C. A comprehensive respiratory panel showed positivity for Mycoplasma pneumonia. Thus, a diagnosis of cold agglutinin syndrome secondary to M. pneumonia was made, and she was started on injection doxycycline 100 mg IV twice a day, following which her symptoms and anemia improved without transfusion support.