No clumping of cells (agglutination), indicating that there are no antibodies to red blood cells, is normal.

Normal value ranges may vary slightly among laboratories. Talk to your doctor about the meaning of your specific test results.

An abnormal (positive) direct Coombs' test means you have antibodies that act against your red blood cells. This may be due to:

• Autoimmune hemolytic anemia without another cause
• Chronic lymphocytic leukemia or other lymphoproliferative disorder
• Drug-induced hemolytic anemia (many drugs have been associated with this complication)
• Erythroblastosis fetalis (hemolytic disease of the newborn)
• Infectious mononucleosis
• Mycoplasmal infection
• Syphilis
• Systemic lupus erythematosus or another rheumatologic condition
• Transfusion reaction, such as one due to improperly matched units of blood

The test is also abnormal in some people without any clear cause, especially among the elderly. Up to 3% of people who are in the hospital without a known blood disorder will have an abnormal direct Coombs' test.

An abnormal (positive) indirect Coombs' test means you have antibodies that will act against red blood cells your body views as foreign. This may suggest:

• Autoimmune or drug-induced hemolytic anemia
• Erythroblastosis fetalis hemolytic disease
• Incompatible blood match (when used in blood banks)