There are several reasons why errors may occur when determining blood grouping.
Three groups stand out among them:
- biological characteristics of the blood under test;
- technical errors;
- use of defective standard erythrocytes and standard sera.
Consider each of the groups more details.
Technical errors in blood typing include:
- incorrect recording of test blood;
- incorrect ratio of erythrocyte and serum volumes;
- dirty plates and other items in contact with blood. A separate pipette is used for each serum, washing is performed with 0.9% sodium chloride solution;
- incorrect placement of sera on a plate or plate;
- over- or undercentrifugation;
- incorrect accounting of the time required for the agglutination reaction to pass;
- lack of agglutination due to ambient temperatures above 25 ºC.
To obtain unreliable results that depend on the use of inferior standard sera and erythrocytes include:
- the use of non-sterile or insufficiently preserved erythrocytes or sera, the use of which provokes non-specific “bacterial” agglutination;
- use of weak sera with an expired expiration date or with a titer lower than 1:32, which can cause weak or late agglutination.
Blood typing errors due to the biological characteristics of the studied red blood cells include:
- “weak” forms of erythrocyte antigens, which are the cause of weak and late agglutination. To identify A2 agglutinogen in a simple reaction, a repeat test should be performed using a different batch of tsoliclones, using a different glassware and increasing the registration time;
- “Autoagglutination” (“panagglutination”) – the ability of blood to show an identical non-specific reaction with all sera, including one's own. It is most clearly manifested during the first 5 minutes of the reaction. The problem can be solved by washing the studied erythrocytes three times;
- “coin columns” into which the erythrocytes of the studied blood sample are added. The addition of a few drops of isotonic NaCl solution is recommended;
- incomplete (mixed) agglutination, in which some of the red blood cells remain free, and some agglutinate.
To errors due to biological characteristics of the studied serum include:
- the absence of anti-A and anti-B antibodies, which occurs in patients with suppressed humoral immunity and in newborns;
- agglutination of standard erythrocytes due to the presence of nonspecific and specific cold antibodies. Serum interacts with various samples of standard erythrocytes, including group 0 (I). To determine the specificity of antibodies, a study is carried out with a panel of erythrocytes typed according to the P, MNS systems;
- detection of antibodies that appeared as a result of previous sensitization. The recipient needs a personal selection of the donor's blood;
- identification of “coin columns” of standard erythrocytes. The problem is solved by adding isotonic NaCl solution. To determine the “coin columns”, you need to add a couple of drops of isotonic sodium chloride solution and gently shake the plate or tablet. The “coin columns” are destroyed.
For more information about errors in determining blood groups, see the website of Sangvitest LLC.