The Coombs test or antiglobulin test is a blood test that looks for antibodies in your blood that are either free flowing (indirect Coomb test) or that may stick to your red blood cells (direct Coombs test)  and may cause red blood cells to die too early. It is often part of a routine prenatal blood test panel.

There are two types of the Coombs test: Direct Coombs Test and Indirect Coombs Test

• The direct Coombs test is used to detect antibodies that are stuck to the surface of red blood cells. Many diseases and drugs can cause this. These antibodies sometimes destroy red blood cells and cause anemia. Some of the diseases associated with a positive direct Coombs test include: Hemolytic anemia; Chronic lymphocytic leukemia or similar disorder; Infectious mononucleosis; Mycoplasmal infection; Syphilis; Systemic lupus erythematosus; Transfusion reaction, such as one due to improperly matched units of blood; The test may also be abnormal without any clear cause, especially among the elderly.
• The indirect Coombs test looks for free-flowing antibodies against certain red blood cells. It is important especially during pregnancy to know if the indirect Coombs test is positive because these antibodies can potentially move across the placenta to the fetus and attack it's blood.The next step is usually to identfy exactly which antibodies those are and whether they can do potential harm to the fetus during pregnancy.