The main difference between direct and indirect Coombs test is that the direct Coombs test detects the antibodies or the complement proteins attached to the surface of red blood cells whereas the indirect Coombs test detects antibodies against foreign blood cells in the serum. Furthermore, the direct Coombs test helps to test for autoimmune hemolytic anemia in which the immune system breaks down red blood cell, causing anemia. In contrast, the use of indirect Coombs test is in blood transfusion and prenatal testing of pregnant women.
Direct and indirect Coombs test are the two types of Coombs tests, which are clinical blood tests used in immunohematology.
Key Areas Covered
1. What is Direct Coombs Test
– Definition, Importance, Procedure
2. What is Indirect Coombs Test
– Definition, Importance, Procedure
3. What are the Similarities Between Direct and Indirect Coombs Test
– Outline of Common Features
4. What is the Difference Between Direct and Indirect Coombs Test
– Comparison of Key Differences
Key Terms
Antibodies, Autoimmune Hemolytic Anemia, Blood Transfusion, Direct Coombs Test, Indirect Coombs Test, Red Blood Cells
What is Direct Coombs Test
Direct Coombs test is a type of clinical blood test used to detect the antibodies or complement proteins attached to the red blood cells. The test helps to determine whether the origin of the hemolytic anemia is auto immunogenic. Generally, in hemolytic anemia, the breakdown of red blood cells occurs at a higher rate, causing anemic conditions. Autoimmunity can be a cause for hemolytic anemia. That means; immune system components like antibodies and complement proteins cause the destruction of red blood cells. And, this test allows the detection of these components of the immune system attached to the red blood cells.
Figure 1: Direct and Indirect Coombs Test
During the direct Coombs test, the red blood cells are washed to remove the blood plasma. Thus, this removes the dissolved antibodies and complement proteins in the serum. Next step is to incubate these red blood cells with the Coombs reagent, which contains anti-human globulin. The binding of anti-human globulin to the human antibodies or complement proteins on the surface of the red blood cells results in the agglutination of the red cells. It visually indicates the positive results of the direct Coombs test; indicating the auto immunogenic version of hemolytic anemia. However, hemolytic anemia with negative results in the direct Coombs test indicates that this type of hemolytic anemia is not mediated by the immune system.
What is Indirect Coombs Test
Indirect Coombs test is the other type of Coombs test used to detect antibodies produced against foreign red blood cells. It is used in testing prior to a blood transfusion and in prenatal testing of pregnant women. In general, our immune system produces antibodies in response to foreign substances. Here, the antibodies produced against foreign red blood cells remain in the serum. Foreign red blood cells can enter the body during a blood transfusion. Moreover, the type of red blood cells of the fetus may differ from the red blood cells of the mother. Therefore, the indirect Coombs test is important in the detection of the immune reaction to the foreign red blood cells.
During the indirect Coombs test, the first step is to incubate the serum with the foreign red blood cells known antigenicity. Next is the addition of the Coombs reagent or the anti-human globulin. If red blood cells become agglutinated, the test is positive, and if not, the test is negative. Positive results mean the presence of antibodies against foreign red blood cells and negative results mean the absence of such antibodies.
Similarities Between Direct and Indirect Coombs Test
- Direct and indirect Coombs test are the two types of Coombs tests.
- They are two types of clinical blood tests that help to test different conditions related to red blood cells.
- Also, both tests use an anti-human globulin also known as “Coombs reagent”. And, this anti-human globulin binds to the human antibodies including IgG and IgM.
- Agglutination of red blood cells is the observation for the positive result for both types of tests.
Difference Between Direct and Indirect Coombs Test
Definition
Direct Coombs test is a type of clinical blood test used to detect the antibodies or complement proteins attached to the red blood cells. Indirect Coombs test, in contrast, is another type of Coombs test used to detect antibodies produced against foreign red blood cells. Thus, this is the main difference between direct and indirect Coombs test.
Components Detected by the Test
Moreover, direct Coombs test detects antibodies or complement proteins attached to the red blood cells while the indirect Coombs test detects the developed antibodies against foreign red blood cells. Hence, this is another difference between direct and indirect Coombs test.
Type of Components of Blood Being Tested
Also, washed red blood cells without plasma are used in the Direct Coombs test while serum is used to the indirect Coombs test.
Uses
Another difference between direct and indirect Coombs test is that direct Coombs test detects autoimmune hemolytic anemia while the indirect Coombs test is used prior to the blood transfusion and in prenatal testing of pregnant women.
Conclusion
Direct Coombs test is a type of clinical blood test that helps to detect antibodies or complement proteins attached to red blood cells. On the other hand, the indirect Coombs test is another type of clinical blood test that helps to detect antibodies developed against foreign red blood cells. Therefore, the main difference between direct and indirect Coombs test is the use of the test.
References:
1. “What Is a Coombs Test? – Definition, Direct & Indirect.” Study.com, Study.com, Available Here
Image Courtesy:
1. “Coombs test schematic” By No machine-readable author provided. A. Rad~commonswiki assumed (based on copyright claims). – No machine-readable source provided. Own work assumed (based on copyright claims). (CC BY-SA 3.0) via Commons Wikimedia
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