There have been rapid technological advances in blood banking in our region over the past decade with an increasing emphasis on quality and safety of blood products. The conventional pre-transfusion testing techniques in immunohematolgy are quite cumbersome. The most commonly employed, tube technique, though still considered as a gold standard has some inherent limitations in the form of; elution of low affinity antibodies during washing, variability in the red cell concentrations, improper cell serum ratio, and lack of consistency in reporting the results due to inter observer variability.[1
] The introduction of newer techniques such as column agglutination technique (CAT), Solid Phase Red Cell Adherence Assay (SPRCA), and erythrocyte-magnetized technique (EMT) have tried to overcome these short comings and bring about an improvement in the quality of testing and the reproducibility of results.[1
] These new technologies are amenable to automation and major manufacturers in this field have come up with user-friendly semi-automated and fully automated equipments for immunohematology tests with varying throughputs depending upon the work load of a blood bank. We, here, present a brief introduction of major equipments available and the requirements for shifting from the conventional technology to the automated systems.
Automation in Blood bank serology was introduced in the developed countries in the 1960s.[4
] Automation in blood banks is being adopted by more and more centers and is rapidly becoming a standard testing technology in developed nations.[5
] In India automation has come up in a big way with the larger centers shifting to totally automated platforms for serologic testing. Automation provides the advantage of improving quality of testing by:[6
- Decreasing human errors in sample identification which has often been quoted as a significant cause of near miss events and transfusion reactions due to mismatched blood transfusion.
- Reducing human errors while performing tests and subjective variations during interpretation of results.
- Preventing transcription errors during documentation of results.
- Improving objectivity, reproducibility, and storage and retrieval of results of immunohematology tests.
- Improving traceability of all variables during testing including, samples, reagents and operating staff.
- It reduces manual input and therefore results in manpower economy.
- High throughput devices with lesser turnaround time improve the quality of services in large tertiary care settings.
The selection of the optimum equipment for a blood center depends on the workload, resources, and space available. In India at present the following manufacturers are providing fully automated and semi-automated Immunohematology platforms:
- BIO-RAD (Switzerland) - IH-1000/Techno Twin Station/Saxo ID Reader.
- DIAGAST (France) - Qwalys 3/FREELYS Mini Lab.
- Ortho-Clinical Diagnostics (Johnson & Johnson, USA) - Autovue Innova/Biovue.
- IMMUCOR (USA) - Galileo/NEO.
- Grifols (Singapore) - WADIANA/Semi-automated.
The automated platforms from BIO-RAD, Ortho-Clinical Diagnostics, and Grifols are based on the column agglutination technology. The IMMUCOR platform is based on SPRCA principle, while DIAGAST is based on the innovative erythro-magnetic technology. The detailed methods are described below:
Column Agglutination Technology[1
] : The column agglutination test system consists of a plastic card with six to eight inbuilt microtubes. The microtubes have a broad reaction chamber in the upper part, while the lower part contains either a clear gel (BIO-RAD and Grifols) or a glass microbead matrix (Ortho-Clinical). Antihuman globulin (AHG) or other antisera are incorporated in the gel or microbead matrix as per requirements for a particular test. A weak suspension (0.8–1%) of red cells is prepared in a low ionic strength solution (LISS) and a measured amount of red blood cell (RBC) suspension is mixed with plasma. The cards are incubated if required and then centrifuged. The sensitized red cells agglutinate in the presence of AHG in the gel/bead matrix and get trapped while unsensitized cells form a button at the bottom of the microtube. The reactions may be graded from 1 + to 4 + and a card reader if used provides objectivity to the grading. Omission of the washing steps during testing reduces the turnaround time and elution of antibodies. The tests results may be preserved for up to 24 h in the testing card, however, they can be stored for longer periods in electronic formats. The column agglutination system is an open system and can fulfill a variety of red cell serology testing requirements.
Solid Phase Red Cell Adherence Assay[1
]: This is a technique in which one of the components of an antigen–antibody reaction is immobilized onto a solid medium and after reaction with a free antigen/antibody the end point of the reaction is indicated by use of red cells, which may be a part of the antigen–antibody reaction or may be added as indicator cells. In forward grouping U shaped micro plate wells are coated with Anti-A antiserum, Anti-B antiserum, and Anti-D antiserum, A drop of 0.5% bromelin-treated red cells are added to the well. On centrifugation antigen positive cells spread out while antigen negative cells form a button at the bottom of the well. In case of reverse grouping a monolayer of RBC membrane is attached to the bottom of the well and plasma to be tested is added after incubation for 5 min, the excess plasma is blotted and anti-IgG bound indicator red cells are added to give a visible reaction. SPRCA may be adapted to other red cell serology tests such as antibody screening, identification, and cross matching. It may also be adapted to platelet serology.
] : This technology is based on the magnetization of RBCs. Paramagnetic particles are adsorbed on to the surface of RBCs. Once antibodies in plasma/antisera react with antigens on RBCs in a micro plate well a magnetic force is applied at the bottom of the microplate using a magnetic plate, this causes the RBCs to be pulled toward the bottom of the microplate. In this manner the magnetic force replaces the centrifugation step. On shaking/resuspension the reactions may be deciphered. In forward grouping the test RBCs are suspended in a solution of iron chloride and bromelin, then the RBC suspension is dispensed into the microplate well precoated with antisera. This is followed by gentle shaking and incubation for 10 min, and then the microplate is put on a magnetic plate. The magnetized RBCs gather at the bottom of the plate. On shaking after this step the free RBCs are resuspended while agglutinated RBCs form a button at the bottom of the well. In case of reverse grouping premagnetized RBCs are mixed with test plasma in the microplate wells followed by the same steps as above. This technology may also be adapted to antibody screening and identification.
All the above described methods have reduced the manual input in putting up various serology tests and hence improved the laboratory efficiency. The gel (CAT) has shown a sensitivity as compared with conventional test tube (CTT) methods (93.5-100% for CAT vs. 50% for CTT).[11
] The sensitivity of SPRCA has been found to be superior to CTT and comparable with that of CAT.[14
] EMT is a relatively recent technology and not much has been published about it. In the available studies, it has been shown a performance comparable with that of gel CAT.[3
] A comparison of the newer technologies with the conventional tube testing has been compiled in
] The newer methods have added to the quality of testing but none of the methods has been found to be unequivocally superior to others. Detection of all antibodies during antibody screening is not the goal of antibody screening; rather detecting all clinically significant antibodies should be the aim for any technology, as detection of insignificant antibodies adds to the burden of further work up and delay in providing blood to the patients.[8
] While selecting an appropriate technology for automation there are a number of other issues to be considered and are discussed later.
Table 1 Comparison of technologies used for immunohematology tests[1,7–10,14,15]
There are several fully automated immunohematology work stations available at present which differ in the technology used, configuration of the immunohematology tests, throughput, turnaround time, sample loading options, priority sample facility. A comparison of the major fully automated immunohematology work stations available in our region has been compiled in . The information given in the table has been taken from the product literatures and the vendors. The decision to buy an automated system depends on the location of the blood bank, type of services provided; cost issues, space availability, staff competency, and feedback regarding the equipment and services of the vendor. We will be discussing the major issues one by one.
Comparison of Fully Automated Immunohematology Workstations