Any Other Information
1) Result Interpretation
An abnormal (positive) indirect Coombs test means you have antibodies that will act against red blood cells that your body views as foreign.
A positive test result means that your blood is incompatible with the donor's blood and that you cannot receive blood from that person.
A normal (negative) result means that the mother has not developed antibodies against the fetus's blood. A negative Coombs test indicates that the fetus is presently not in danger from problems relating to Rh incompatibility.
For qualitative methods, the interpreter examines the test tube and assigns a score based on a graded scale:
M: Mixed field – any degree of agglutination in a pool of non-agglutinated cells.
W: tiny aggregates, background is turbid ,reddish
1: small aggregates, background is turbid reddish
2: small to medium-sized aggregates, background isvclear
3: several large aggregates, background is clear
4: aggregate or clump of cells.
2) What are the uses of ICT?
It is used to detect very low concentrations of antibodies present in a patient's plasma/serum before a blood transfusion. The IAT can also be used for compatibility testing, antibody identification, RBC phenotyping, and titration studies.
The ICT can detect IgG antibodies in the Rh, Kell, Kidd and Duffy systems. If clotted specimens and polyspecific AHG are used, it can also detect IgM antibodies that can bind C3 such as anti-Lea, anti-Leb, autoanti-I and anti-P1.
3) What are the uses of ICT in antenatal care?
In antenatal care, the IAT is used to screen pregnant women for antibodies which may cause hemolytic disease of the newborn. An indirect Coombs test may be used to determine whether there are antibodies to the Rh factor in the mother's blood. In this case, A normal (negative) result means that the mother has not developed antibodies against the fetus's blood.
4)What is the difference between direct and indirect Coombs test?
The direct Coombs test is performed on a sample of red blood cells from the body. The indirect Coombs test is performed on a sample of the liquid part of the blood (serum). It detects antibodies that are present in the bloodstream and could bind to certain red blood cells, leading to problems if blood mixing occurs.
5) What happens in ICT?
In indirect antiglobulin testing, serum from a blood sample is isolated, and native RBCs are removed. The isolated serum sample is then incubated with foreign RBCs of known antigenicity. Antiglobulin reagent is then added, and the presence of agglutination is indicative of a positive result.
6) What is the procedure for ICT?
- 4% OF saline suspension of the test cells is prepared.
- Two drops of cell suspension is then added to a small test tube.
- Two drops of antiserum is added to the cell suspension.
- It is incubated in a water bath at 37°C for 30 minutes
- The tube from the water bath is removed and washed around 3 to 4 times with large volume of saline. It is completely decanted after last washing.
- Two drops of anti-human globulin (AHG) is added immediately and mixed well.
- It is centrifuged at 1500 rpm for one minute and examined for haemagglutination.
- In case of negative haemagglutination, pre-sensitized reagent cells is added to test the reactivity of AHG. Agglutination must be seen with the addition of Coombs’ control cells.
7) What are the limitations of the procedure?
Inadequate washing of the red cells, contamination with human serum protein of the anti-serum, incorrect incubation or centrifugation times and inadequate temperature ranges may give false negative reactions. The Test cells, which have a positive Direct Antiglobulin Test, will also give a false positive reaction with all Indirect Antiglobulin Tests. Test serum should not be stored for longer than 24 hours at 2-8ºC or 1 month at –20ºC in order to detect complement-binding antibodies. The reagent will not agglutinate red cells coated with C4d fragments. No single test can be capable of detecting all clinically significant antibodies. The reagent must be used as supplier without dilution or addition. - Use of reagents and interpretation of results must be carried out by properly trained and qualified personnel.
8) What is the coombs reagent?
Coombs reagent (also known as Coombs antiglobulin or antihuman globulin) is used in both the direct Coombs test and the indirect Coombs test. Coombs reagent is an antihuman globulin. This reagent is made by injecting human globulin into animals, which produce polyclonal antibodies specific for human immunoglobulins and human complement system factors. There are more specific Coombs reagents or monoclonal antibodies, which can be used.
9) What happens if ICT test is positive during pregnancy?
The antibodies kill the Rh-positive red blood cells. If the patient gets pregnant with an Rh-positive baby (fetus), the antibodies can destroy the fetus's red blood cells. This can cause anemia.
10) Which are the confounding variables that affect the accuracy of DAT and the Type of antibody present
Most commercial antiglobulin tests screen for antibodies to IgG, complement C3, or both. As such, false-negative results may occur in cases of AIHA caused by autoantibodies other than IgG or C3, such as IgM or IgA.
Amount of antibody present - in some rare cases, autoimmune anemia may be induced by levels of antibody below the detection limit of DAT, which is approximately 150 to 500 molecules of IgG per red cell Thus, RBCs may undergo phagocytosis when opsonized by a level of antibody below the threshold of detection, resulting in a falsely negative result.
High serum protein - certain conditions, such as myeloproliferative diseases, may cause a falsely positive agglutination study due to abnormally high levels of protein unrelated to antibody-RBC agglutination. Exogenous sources of excess protein or immunoglobulin, such as cases in which a patient is receiving intravenous immune globulin (IVIG), may also result in a falsely positive result.
Infection - the serum of individuals infected, certain microorganisms may create a false positive agglutination result. Examples for these include human immunodeficiency virus (HIV), malaria, hepatitis C virus (HCV), and in rare cases, the hepatitis E virus (HEV)
Antiphospholipid syndrome - cross-reactivity between antiphospholipid antibodies and RBC membranes can result in falsely positive DAT testing.
Wharton Jelly - in neonatal umbilical cord blood samples, the presence of mucopolysaccharide-rich Wharton’s Jelly has been shown to produce false-positive antiglobulin result.
care.phadkelabs@agilus.in
9111591115
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