Gel Card and Saline Tube Techniques for Blood Cross-Matching: A Comparative Assessment Study

Introduction

ABO blood grouping system was discovered by Landsteiner during 1901 and the first anti-globulin test was performed in 1945. Since then, more specific serological methods are being developed and to avoid ABO and Rh incompatibility between blood donors and recipient¹ and also to analyze the presence of any antibody in recipient serum which can react with donor red cells and can cause serious complications after blood transfusion.² The purpose of cross match is to select blood component that will have acceptable survival when transfused and will not cause any adverse reaction to the recipient.

Compatibility testing or cross matching is performed to ensure safe transfusion therapy. Cross matching is an integral part of routine pre transfusion testing. The terms “cross matching” and “compatibility test” are sometimes used interchangeably. It is necessary to perform cross match as final serological test of incompatibility even if the blood group of recipient and donor are known, because this will show if any mistakes have been done in ABO grouping, which may cause fatal hemolytic transfusion reactions.³

The Conventional tube technique (CTT) has been the cornerstone of compatibility testing over last 40 years, but the enhanced sensitivity of the gel card technique has made the interpretation of the tests more objective.⁴ Lappiere et al. introduced the gel card method which is used for cross matching of blood along with saline tube method. The gel card is a reliable, advantageous method and suitable for routine use to detect and identify the alloantibody.⁵

Sephadex gel is used in gel cards which holds agglutinate in semisolid medium and helps in clear visualization of agglutination than that of tube method [4]. When RBCs are added on to a gel card, gel acts as a trap. RBCs which agglutinate are seen trapped in gel at the bottom of the tube, which can be seen for hours. For easy handling, reading and testing there are 6 micro tubes in a single gel card.

Aim of this study is to compare the accuracy and sensitivity of gel card technique (LISS / COOMBS) and saline tube method, also to assess the compatibility test by gel card and saline tube method with coomb’s and without coomb’s test.

Materials and methods

The present study was carried out at Mallasandra urban primary health care center, Bangalore Karnataka in India to evaluate the matrix gel card technique and compare the matrix gel card method with conventional tube method for pre transfusion compatibility testing.

A total of 100 samples were collected, and compatibility testing was done using CTT and gel card Method. Donor samples were collected from the pilot tubes of the blood donations collected from healthy donors with >45 kg body weight having negative serology of HIV, HBsAg, HCV, VDRL and Malaria. Patient samples were received from the ward with the blood requisition form.

Cross-matching was carried out using the technique given below. Blood grouping of patient blood and donor blood with the help of anti-sera A, B, D was done. After confirmation of blood group, cross matching of both donor and patient’s blood was carried out by two methods - spin saline tube method with and without AHG reagent and Matrix Gel card method.

All samples were cross matched by the following techniques:

1. Saline Tube Method: Major and minor cross match was performed using saline tube method. After preparing 5% red cell suspension, cross matching was done by adding serum and red cell suspension in the ratio of 2:1 and incubated at 37°C for 30-60 minutes. The tubes were centrifuged and observed for agglutination. The cells were washed 3-4 times to remove any unbound antibody. After adding AHG, the tubes were centrifuged, and were observed for agglutination. Check cells were added to all negative tubes for cross verification.

2. Gel card technique for Coombs test - The micro tubes of the ID-Card LISS / Coombs containing poly specific AHG, were used for cross matching. Patientserum and donor red cells were added to the micro tubes. The card was incubated at 370 C for 15 minutes, centrifuged for 10 minutes and results were observed.

Statistical Analysis was carried out using frequency percentage and chi square test.

Results

In our study, 100 blood samples were cross-matched using Spin saline tube method with and without AHG and Matrix Gel Card. We compared both methods of cross-matching for sensitivity & specificity, the accuracy of results, and time taken. 96 (99.2%) samples were compatible, and 04 (0.8%) samples were incompatible in Gel card method. In CTT, 94 samples were compatible, and 06 samples were incompatible without AHG. In CTT with AHG 96 (99.2%) samples were compatible and 04 samples (0.8%) were incompatible.

In our study, both sensitivity and specificity of matrix gel card method was found to be 100%. Whereas sensitivity of CTT without AHG was 100% but specificity was found to be 97.9%. Further positive predictive value and negative predictive value of gel card method was 100% and positive predictive value and negative predictive value of CTT without AHG was 66.6% and 100% respectively.

Discussion

CTT is the most commonly used method for pre-transfusion compatibility testing, but it is associated with certain disadvantages like being laborious and time-consuming method. These are nullified in gel card method.

In our study, 94 samples showed compatibility in CTT without AHG and considered as true negative. Out of 06 samples which were incompatible, 04 samples were found to be incompatible, and 02 samples were compatible, when subjected to CTT with AHG. Hence these two samples appear to be false positive. The findings of our study are in concordance with the studies conducted by Gond SK et al⁰⁶, Singh DN et al⁰⁷, Dhariwal SK et al⁰8, Gulati P et al⁰⁹, Singh R et al¹⁰, Sharma R et al⁰². The benefits of gel cards include simple micro tube reading, convenient long-term recording, handling, and disposal. Hence specificity and sensitivity of Gel card method is found to be higher than CTT without AHG. The Two false positive results can be attributed to technical insufficiency while performing the test. Results of this study is compared with other studies as shown in Table 3.

Conclusion

Gel card is more sensitive and more specific than conventional tube methods and also less time consuming. The results of Gel card method is on par with results of CTT with AHG. This method is simple to perform, gives reliable, reproductive, stable end point result which can be preserved and photocopied for future record. Moreover gel cards are easy to dispose by incineration thus preventing blood bank personnel from exposure to transfusion transmitted diseases.

Gel card method of compatibility testing can be reliable method to check for pre transfusion cross matching in health centers with high workload as it is can be carried out quickly and easily. It can also be used in suspected cases along with CTT with AHG method for confirmation of compatibility in centers which cannot afford routine gel card. As the results of our study were in concordance with previous studies, we conclude that matrix gel card method testing is more sensitive and specific. A larger cohort study is necessary to analyze the efficacy of matrix gel card method over CTT without AHG.

Limitations of the present study: Low sample size and high cost of matrix gel card when compared to CTT method.

Conflict of Interest

Nil

Acknowledgement

We would like to thank; Dr. Jayanthi V, the principal and dean for her encouragement and support, the statistician Mrs. Lavanya, Department of Community Medicine and coordinator/tutor Mr.Vamsi Krishna Tokala, Department of Pathology, Sapthagiri Institute of Medical Science and Research Centre, for valuable information and guidance provided to us in carrying out this research work.