Transcription
We have been talking about autoimmune hemolytic anemia for a while, and you know there are two different types of immune hemolytic anemia: we have the warm subtype and the cold subtype. Direct Coombs test is diagnostic to both the warm and the cold subtypes. So let's get started. So what's our goal? Our goal is to detect antibodies bound to the red blood cell surface. So this is a difference between direct and indirect Coombs test. Direct test detects antibodies on the red blood cell surface; indirect test detects antibodies in the plasma.
So here are the steps: we get some nice red blood cells from a blood sample from the patient. So these are the patient red blood cells; these are covered with antibodies, and these antibodies are contacting the antigens. Then we add something called Coombs reagent, which is antibodies to human globulin; could be against IgG and IgM or the complement. If they agglutinate, that's a positive test; that's a positive direct Coombs test, and it's diagnostic of hemolytic anemia, both the warm and the cold subtype.
Please note: after we agglutinated the test, then we can do something else: the antibody can be eluted from the red cell surface and tested against a panel to determine what type it was: was it an IgG, IgM, or a complement? Okay. Please note that direct Coombs test can be negative in the presence of brisk or fast hemolysis. If the hemolysis occurs rapidly, maybe the Coombs test will be negative in the beginning. Also note that about 10% of warm autoimmune hemolytic anemia patients are Coombs test negative. So just because you have warm autoimmune hemolytic anemia doesn't necessarily mean that the Coombs test will come back positive; it can come back negative in 10% of the patients, or if the hemolysis is rapid in the beginning.
Okay, why do we use direct Coombs test? We use direct Coombs test in many scenarios, such as to diagnose autoimmune hemolytic anemia, as you know, also hemolytic disease of the newborn, as well as transfusion reactions. That's it for the direct Coombs test. See you next video; we will discuss the indirect Coombs test. Thank you.