Tube and slide methods<unk>  typing can be performed using test tubes, microplates, or<unk>  typing slides. The tube method involves mixing a suspension of red<unk>  cells with antisera (or plasma, for reverse grouping) in a test tube. The mixture is centrifuged to separate the cells from the reagent, and then resuspended by gently agitating the tube. If the antigen of interest is present, the red<unk>  cells agglutinate, forming a solid clump in the tube. If it is absent, the red<unk>  cells go back into suspension when mixed. The microplate method is similar to the tube method, except rather than using individual test tubes,<unk>  typing is carried out in a plate containing dozens of wells, allowing multiple tests to be performed at the same time. The agglutination reactions are read after the plate is centrifuged. Antibody screening and identification can also be carried out by the tube method. In this procedure, the plasma and red cells are mixed together in a tube containing a medium that enhances agglutination reactions, such as low ionic strength saline (LISS). The tubes are incubated at body temperature for a defined period of time, then centrifuged and examined for agglutination or hemolysis; first immediately following the incubation period, and then after washing and addition of anti-human globulin reagent. Crossmatching, likewise, may be performed by the tube method; the reactions are read immediately after centrifugation in the immediate spin crossmatch, or after incubation and addition of AHG in the full crossmatching procedure. The slide method for<unk>  typing involves mixing a drop of<unk>  with a drop of antisera on a slide. The slide is tilted to mix the cells and reagents together and then observed for agglutination, which indicates a positive result. This method is typically used in under-resourced areas or emergency situations; otherwise, alternative methods are preferred. Column agglutination<unk>  typing by column agglutination method: type O positive Column agglutination techniques for<unk>  (sometimes called the "gel test") use cards containing columns of dextran-polyacrylamide gel. Cards designed for<unk>  typing contain pre-dispensed<unk>  typing reagents for forward grouping, and wells containing only a buffer solution, to which reagent red<unk>  cells and plasma are added, for reverse grouping. Antibody screening and crossmatching can also be carried out by column agglutination, in which case cards containing anti-human globulin reagent are used. The gel cards are centrifuged (sometimes after incubation, depending on the test), during which red<unk>  cell agglutinates become trapped at the top of the column because they are too large to migrate through the gel. Cells that have not agglutinated collect on the bottom. Therefore, a line of red<unk>  cells at the top of the column indicates a positive result. The strength of positive reactions is scored from 1+ to 4+ depending on how far the cells have travelled through the gel. The gel test has advantages over manual methods in that it eliminates the variability associated with manually re-suspending the cells and that the cards can be kept as a record of the test. The column agglutination method is used by some automated analyzers to perform<unk>  typing automatically. These analyzers pipette red<unk>  cells and plasma onto gel cards, centrifuge them, and scan and read the agglutination reactions to determine the<unk>  type. Solid-phase assay Solid-phase assays (sometimes called the "antigen capture" method) use reagent antigens or antibodies affixed to a surface (usually a microplate). Microplate wells coated with anti-A, -B and -D reagents are used for forward grouping. The test sample is added and the microplate is centrifuged; in a positive reaction, the red<unk>  cells adhere to the surface of the well. Some automated analyzers use solid phase assays for<unk>  typing. Genotyping Genetic testing can be used to determine a person's<unk>  type in certain situations where serologic testing is insufficient. For example, if a person has been transfused with large volumes of donor<unk> , the results of serologic testing will reflect the antigens on the donor cells and not the person's actual<unk>  type. Individuals who produce antibodies against their own red<unk>  cells or who are treated with certain drugs may show spurious agglutination reactions in serologic testing, so genotyping may be necessary to determine their<unk>  type accurately. Genetic testing is required for typing red<unk>  cell antigens for which no commercial antisera are available. The AABB recommends RhD antigen genotyping for women with serologic weak D phenotypes who have the potential to bear children. This is because some people with weak D phenotypes can produce antibodies against the RhD antigen, which can cause hemolytic disease of the newborn, while others cannot. Genotyping can identify the specific type of weak D antigen, which determines the potential for the person to produce antibodies, thus avoiding unnecessary treatment with Rho(D) immune globulin. Genotyping is preferred to serologic testing for people with sickle cell disease, because it is more accurate for certain antigens and can identify antigens that cannot be detected by serologic methods. Genotyping is also used in prenatal testing for hemolytic disease of the newborn. When a pregnant woman has a<unk>  group antibody that can cause HDN, the fetus can be typed for the relevant antigen to determine if it is at risk of developing the disease. Because it is impractical to draw<unk>  from the fetus, the<unk>  type is determined using an amniocentesis sample or cell-free fetal DNA isolated from the mother's<unk> . The father may also be genotyped to predict the risk of hemolytic disease of the newborn, because if the father is homozygous for the relevant antigen (meaning having two copies of the gene) the baby will be positive for the antigen and thus at risk of developing the disease. If the father is heterozygous (having only one copy), the baby only has a 50% chance of being positive for the antigen.
Blood compatibility testing
Hematology analyzer
Calibrated automated thrombogram
Blood smear
Drug test
Viral disease testing
Iron tests
Clinical chemistry