Comparison of gel test and conventional tube test for antibody detection and titration in D-negative pregnant women: study from a tertiary-care hospital in North India

Conventional tube testing was used for antibody screening and titration in D– pregnant women in our hospital until the recent introduction of the gel test. In this study we assessed the sensitivity of the gel test in our setup and tried to establish a correlation between these tests for determining antibody titer. We collected 652 blood samples from 223 antenatal D– women during a span of 1 year. The samples were tested separately by the conventional tube technique and the gel test for antibody detection and titration. The tube test detected 84 (12.8%) positive samples as compared with 93 (14.2%) by gel test, indicating the latter to be more sensitive (p < 0.01). The gel test picked up weakly reactive anti-D that the tube test missed. We did not use any enhancing media such as LISS in titration studies performed by either method in an effort to establish a correlation. However, much higher titers (one- to fivefold) were obtained by the gel test with no clear correlation with the corresponding tube values. When comparing the titer values to the finding of hydrops on ultrasound and Liley’s chart OD reading on amniocentesis, a value of less than 128 (i.e., 64) by gel test corresponded to normal results. Through this study, we thus conclude that the gel test is more sensitive for antibody detection, although a linear correlation could not be established for titers. Clinical correlation may point toward a critical titer of 64 for the gel test, but further studies need to be done to support this finding. Immunohematology2010;26:174–77.