European Journal of Cardiovascular Medicine

Ensuring compatibility through pretransfusion testing is crucial for patient safety during blood transfusions.⁽¹⁾ The primary objective of blood transfusion services is to provide safe, compatible, and adequate blood supplies.⁽²⁾ Compatibility testing helps prevent transfusion reactions caused by of incompatible donor red cells that might result in an immune mediated hemolytic transfusion reaction.⁽³⁾ Since the discovery of the ABO system and red cell agglutination by Landsteiner in 1900 and development of the antiglobulin test by Coombs et al. in 1945, the immune hematologists are trying to establish and improve various serological investigations in human blood.⁽⁴⁾

Historically, the conventional spin tube method has been widely used for crossmatching, often involving enhancement techniques such as bovine albumin, enzymes, and the indirect antiglobulin test (IAT) using anti-human globulin (AHG).⁽⁵⁾ In contrast, the gel card method, developed by Lapierre, relies on controlled centrifugation of red blood through Sephadex gel contained within a microtube. The gel technique is useful for ABO and Rh typing, cross‑matching direct antiglobulin tests and IATs, and identification of alloantibodies.⁽⁶⁾

While the conventional method is still regarded as the standard, it has limitations, including potential antibody elution during washing, variable serum-to-cell ratios, and inconsistent interpretation due to observer subjectivity.^(7,8) The gel card method addresses these issues by offering faster testing, ease of result interpretation, long-term result retention and suitability for automation, though it comes at a higher cost.^(9,10)

This study aims to evaluate and compare the clinical utility of the gel card method versus the conventional tube technique in compatibility testing.

Aim and Objective

To assess the efficiency and reliability of the gel card method compared to the conventional tube method for blood compatibility testing.

This is a retrospective data-based study of samples received between 1^st January 2022 to 31^st March 2022, included 1048 samples referred for crossmatching to a tertiary care hospital's blood bank.

Materials used: Donor and recipient blood samples, test tubes, microscope slides, Gel card and tabletop centrifuge, Incubator, ABO and RhD antisera, Coombs reagent (AHG), Coombs gel cards, Normal saline, Diamed centrifuge.

Testing procedures:

1. Conventional Tube Method (Saline Method):

A 2–4% red cell suspension was prepared. Two drops of recipient serum and one drop of red cell suspension were mixed in a labeled tube, incubated at 37°C for 30–50 minutes, and centrifuged at 1000 RPM for 1 minute. The sample was examined for agglutination or hemolysis, and all negative results were confirmed microscopically.

1. Conventional Tube Method with Anti Human Globulin (AHG):

Similar to the saline method, with additional steps: after incubation and centrifugation, cells were washed three times to remove unbound antibodies. Two drops of AHG reagent were added, followed by another centrifugation and observation. IgG-coated control cells were added to all negative tests for confirmation.

1. Gel Card Method:

1ml of LISS (Low Ionic Strength Solution) was taken to which 10 micro liters of donors packed cells were added in same tube (0.8% cell suspension). 50 micro liters of prepared donors 0.8% cell suspension & 25 micro liters of patient's serum were added in Coombs card. (Cells are always added prior to the serum). Coombs card were incubated at 37°C for 15 mins and then centrifuged at 1000 RPM for 10 minutes in the Diamed centrifuge.

Results were observed and graded:

• No agglutination – compatible
• Agglutination – incompatible
• Grade 4: solid band at the top
• Grade 3: agglutinates in upper half
• Grade 2: agglutinates throughout the column
• Grade 1: agglutinates mainly in the lower half

All samples underwent crossmatching using both conventional (saline and AHG) and gel card techniques.

In our study, 1048 blood samples were cross-matched using Conventional Tube Method without ( (Saline Method) and with AHG and Gel Card method. Various observations of the study are explained in tables below.

Table 1. Sex distribution of the cases

Table 1 shows, out of 1048 cases, majority cases were female 68% and 32% were male. Male to female ratio was 1:2.1.

Table 2. Age distribution of among cases

Table 2 shows, out of 1048 cases, most of cases (24%) belong to age group of 21 to 30 years followed by 31 to 40 years (20%), more than 50 years (16%), 41 to 50 years (15.5%), 1 to 10 years (12%), 11 to 20 years (9.5%) and up to one year (3%) respectively.

Table 3: Observation seen on different crossmatch methods.

Table 3 shows that Out of 1048 samples, 1040 (99.23%) samples were compatible and 08 (0.76%) samples were incompatible in Gel card method and conventional tube technique with AHG, but in CTT (Saline method), 1046 (98.8%) samples were compatible, and 02 (0.2%) were incompatible. Incompatibility of another 06 (0.57%) samples appeared after incubation with AHG reagent at 37◦C saline tube method and the same samples case positive with gel card method as well.

Table 4: Comparison of Sensitivity and Specificity of different cross matching methods.

Table 4 shows that the sensitivity of all three crossmatch methods is 100% but specificity of Conventional Tube Technique without AHG (Saline method) is 99.8% and while that of gel card and Conventional Tube Technique with AHG is 100%.

Table 5 - Time taken by different methods

Table 5 shows The average time taken by Gel card method was 30 minutes for a single compatibility test whereas in conventional tube method with the use of AHG (IAT), average time required was 68 minutes and without AHG it was 45 minutes.

The study aimed to compare blood cross-matching using the gel card method against the traditional tube technique. Blood samples from 1048 patients were tested with all three approaches. In a referenced study by Sharma PK et al.⁽¹¹⁾, 36% of the subjects were male and 64% were female, yielding a male-to-female ratio of 1:1.7. In our study, 68% of participants were female and 32% were male, with a male-to-female ratio of 1:2.1.

When using the conventional tube method without anti-human globulin (Saline method), 1046 out of 1048 samples were compatible—classified as true negatives. Among the 06 more became incompatible with CTT plus AHG, while the remaining, suggesting these were false negatives.

With the gel card method, 1040 samples were compatible (true negatives), and 08 were incompatible (true positives), closely matching the results of the tube method.

These outcomes align with earlier research by Gond SK et al.⁽⁹⁾, Singh N et al.⁽¹⁰⁾, Dhariwal SK et al.¹²⁾, Gulati P et al.⁽¹³⁾, Singh R et al.⁽¹⁴⁾, Ranjitha V et al.⁽¹⁵⁾, and Sharma PK et al.⁽¹¹⁾.

In our study, the gel card method achieved 100% sensitivity and 100% specificity compared to the tube method—results consistent with Sharma R et al.⁽¹⁶⁾, and Gulati P et al.⁽¹³⁾. Additionally, the conventional tube method with AHG showed 100% sensitivity and 99.8% specificity, comparable to findings by Sharma PK et al.⁽¹¹⁾, who reported 100% sensitivity for the gel card and 99.5% for the saline tube method.

In our study the average time taken for the compatibility test for gel card and convention tube technique was 30 min and 68 min respectively which is comparable with the study of  Sharma PK et al⁽¹¹⁾ in which average time required for a single compatibility test by Gel card method was approximately 30 minutes while that for conventional spin tube method was approximately 64 minutes including use of AHG (IAT).

Gel card technology has revolutionized serological testing by offering a more sensitive, standardized, and automation-friendly platform. One of its key strengths lies in its superior sensitivity, particularly for clinically significant IgG antibodies, which may be weak or missed in the conventional tube method. This feature enhances patient safety by reducing the risk of undetected alloantibodies in crossmatching or antibody screening.

Moreover, the gel method is highly reproducible, with less inter-operator variability, as interpretation does not rely heavily on subjective visual reading. The results are clear-cut: agglutinates trapped at the top of the gel column indicate positivity, while a pellet at the bottom suggests a negative result. This clarity greatly reduces the risk of misinterpretation and improves quality control. Additionally, smaller volumes of both sample and reagents are sufficient, which is particularly advantageous in pediatric and resource-conscious settings.

Another major benefit of gel card systems is their compatibility with automated platforms, making them ideal for high-throughput laboratories. The reduced manual workload and shorter hands-on time enhance laboratory efficiency and reduce the chances of technical errors.

However, these advantages come with some drawbacks. Gel cards and the associated equipment involve higher upfront and running costs, which may be prohibitive for smaller or resource-limited settings. Furthermore, the method may have slightly reduced sensitivity to complement-mediated IgM antibodies, though this is generally less significant clinically, as IgG antibodies are the primary concern in transfusion reactions and crossmatching.

On the other hand, the tube method, while cost-effective and simple, is more suited to low-volume laboratories or resource-constrained environments. It remains particularly effective for the detection of IgM antibodies in the immediate spin phase, which can be important in certain clinical scenarios such as ABO incompatibility.

Nonetheless, the tube method is labor-intensive and involves multiple manual steps such as incubation, washing, and centrifugation, all of which increase the risk of human error and inconsistent results. Furthermore, the interpretation of weak reactions can be subjective, making the technique operator-dependent and potentially less reliable in detecting low-titer or weakly reactive antibodies.

In conclusion, while both methods have their place in immunohematology, the gel card method outperforms the traditional conventional tube method in view of high-sensitivity applications, standardization, and automated workflows, especially in larger institutions. It minimizes inter-operator variability, simplifies result interpretation, and supports long-term documentation—key features that are crucial for modern transfusion services. Despite its higher cost and equipment needs, wider adoption of gel card technology, especially in developing countries like India, could improve transfusion safety and standardize practices across institutions.

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