The Direct Antiglobulin Test: Still a Place for the Tube Technique?

Abstract

Objectives: Antibodies of different immunoglobulin isotypes, or complement, may coat red blood cells in vivo. They are detected by the direct antiglobulin test (DAT), usually performed by the conventional tube technique. The purpose of this study was to compare the latter technique with the gel test. Methods: Three hundred and ninety–eight consecutive samples, sent to our laboratory for direct antiglobulin testing, were analyzed with the tube technique and the gel test, using reagents from different manufacturers. Eighty–seven samples had been collected from newborns and 23 from fetuses. Results were expressed as positive or negative. Results: In 162 out of 398 cases, the DAT was negative with both methods, whereas in 178 out of 398 cases, the DAT was positive with both techniques using polyspecific antibodies (observed agreement: 84.5%; κ = 0.71). Discrepancies between the two methods were observed in 58 cases: 51 samples appeared as DAT positive using the tube method and negative with the gel test, whereas only 7 were positive exclusively with the gel test. Among the 178 samples that were positive with both techniques, 93 samples showed discordant results when evaluated with monospecific antisera (11 with anti–IgG and 82 with anti–C3d, respectively). The sensitivity of the DAT performed by the gel test, in comparison with the conventional tube technique, was 75.4% (95% confidence interval (CI): 69.4–80.8). 96.8% (95% CI: 92.8–99.0), and 16.3% (95% CI: 9.8–24.9) with polyspecific, anti–IgG and anti–Cd3 reagents, respectively. Conclusions: The gel test appeared to be less sensitive than the conventional tube technique when utilized for DAT, praticularly when C3d was present on red blood cells. These results emphasize that before implementing a new technique in the laboratory, comparison with existing techniques, using different reagents, is mandatory.

Comparison of conventional tube test technique and gel microcolumn assay for direct antiglobulin test: A large study

“…This is consistent with several other studies that have found the DATs by GMA to be more sensitive than those tests performed by CTT at detecting red blood cell-bound IgG (9,21,22). Also, contrary to the results reported by Tissot et al (16), gel showed to be more sensitive at detecting C3d on red blood cells in our study. Moreover, the results of efficiency test calculations confirm that gel is superior to tube for DATs.…”

“…Some authors concluded that this technique is equal to or better than the CTT (9). On the other hand, Tissot et al (16) concluded that the GMA appeared to be less sensitive than the CTT when utilized for DATs.…”

Multi‐centre evaluation of pre‐transfusional routine tests using 8‐column format gel cards (DG Gel®)

“…Six weakpositive DAT were missed by DiaMed-ID ® and one was missed by using the conventional tube technique whereas only three were missed by DG Gel ® . It is important to point out that although there is a trend to replace conventional tube test by microtube gel tests (Lapierre et al, 1990), the former is still a widely used reference method (Tissot et al, 1999).…”

Comparison of DATs using traditional tube agglutination to gel column and affinity column procedures

“…It is not certain if either assay correlates with the clinical sequelae in these patients. When Tissot and colleagues 16 compared DATs with anti-C3d by tube agglutination and gel microcolumn assays, they found that tube agglutination assays were more likely to be reactive, but different sources of anti-C3d were used for the assays. They concluded that the tube agglutination assay was more sensitive for detection of RBC-bound C3d than gel microcolumn assays.…”