A 21-year-old woman is suspected of having mycoplasma pneumonia based on symptoms of a dry cough, fever, normal lung examination but abnormal chest x-ray with bilateral infiltrates. She is also anemic with hemoglobin of 10.5 g/dL, reticulocyte count of 7%, and WBC 12,000/mL. Hemolytic anemia from cold agglutinins is suspected as the cause. Which of the following tests will confirm autoimmune causation as the cause of the anemia?
positive antinuclear antibody (ANA)
positive rheumatoid factor
positive Coombs’ test
The diagnosis of autoimmune hemolytic anemia requires demonstration of immunoglobulin and/or complement in the patient’s RBC. The broad-spectrum Coombs’ test is an excellent screen.