What causes false positive results in antiglobulin testing?
Reasons for a false positive reaction could be the following: (1) improper sample (clotted cells), (2) spontaneous RBC agglutination, (3) elevation of serum immunoglobulin [22,23], (4) administration of intravenous immune globulin [24], (5) elevated serum globulin and blood urea nitrogen levels [25], (6) over …
Which of the following will cause false positive AHG results?
False-positive results may be caused by the following:
- Overcentrifugation or contaminated reagents.
- Insufficient washing of the patient’s RBCs.
- If the test tubes were left to stand following centrifugation or if the RBCs were left in suspension for an extended period before testing.
What is the principle of AHG testing?
Principle of the AHG Test Because antibodies are gamma globulins, an antibody to gamma globulin can form bridges between red cells sensitized with antibody and cause them to agglutinate (Figure 3-1). Since most incomplete antibodies are IgG, polyspecific AHG serum contains anti-IgG.
What is the principle of indirect Antiglobulin test?
[1] For indirect antiglobulin testing, serum from a blood sample gets isolated, and native RBCs removed. The isolated serum sample then gets incubated with foreign RBCs of known antigenicity. Antiglobulin reagent is then added, and the presence of agglutination indicates a positive result.
Which of the following will cause false negative AHG results?
The most common causes for false negative results are improper or under-washing or under-centrifuging the sample that allows residual unbound antibodies to remain in the tube and adsorb the AHG reagent [4].
What is the function of AHG reagent?
This AHG reagent is designed to detect IgG and/or C3b, and/or C3d components on the surface of human red blood cells.
Does AHG detect IgM?
Since the binding of AHG requires warming the sample to 37C, AHG cannot be used to directly detect the binding of IgM antibodies, which tend to elute off the surface of red cells at that temperature.
What does a positive indirect antiglobulin test signify?
An abnormal (positive) result means that the mother has developed antibodies to the fetal red blood cells and is sensitized. However, a positive Coombs test only indicates that an Rh-positive fetus has a possibility of being harmed.
What does DCT positive mean?
Abnormal. Direct Coombs test. A positive result means that your blood has antibodies that fight against red blood cells. This can be caused by a transfusion of incompatible blood. Or it may be related to conditions such as hemolytic anemia or hemolytic disease of the newborn (HDN).
What causes a false negative on the AHG test?
The washes are also decanted well, because residual saline will decrease the efficiency of protein removal. Also, residual saline after the last wash will dilute the AHG serum and can cause a false negative.
When does the AHG phase occur in a blood test?
In classic tube testing, the AHG phase occurs after the serum and red cells have undergone an incubation at 37 o C followed by a washing step to remove free antibodies. During this step, we add anti-human globulin (yes, that’s where “AHG” comes from) to the serum-RBC mix, centrifuge the tube, and examine to see if the AHG agglutinates red cells
What causes a false negative on the antiglobulin test?
The failure to add AHG reagents or the addition of inactive AHG reagents due to improper storage and handling may lead to false negative results. A delay in the addition of AHG after washing can also cause false negatives when bound immunoglobulin and complement come off the RBC.
Why is the washing stage of the AHG test important?
The washing stage is crucial, because if any unbound protein (IgG) remains, it could neutralize the AHG serum and cause a false negative. The washes are also decanted well, because residual saline will decrease the efficiency of protein removal.