Mitogen Stimulated Direct Antiglobulin Test Compared with Traditional Methods for the Detection of Anti-RBC Autoimmunity.

The diagnosis of autoimmune hemolytic anemia (AIHA) is based on a positive direct antiglobulin test (DAT), which is performed by various methods with different sensitivity. Recently mitogen stimulated (MS)-DAT was suggested able to disclose a latent anti-erythrocyte autoimmunity Aims: To compare different traditional (tube, microcolumn and solid phase) and new (mitogen stimulated, MS)-DAT methods in different diagnostic conditions: 54 consecutive cases of hemolytic anemia of suspected autoimmune origin, 28 idiopathic AIHA in clinical remission, and 12 difficult cases of DAT-negative AIHA, and 2) to correlate results with hematologic and hemolytic parameters.

DAT tube, microcolumn, solid phase, and eluates were performed by standard techniques. MS-DAT was performed by stimulating whole blood with PHA, PMA and PWM and antibodies were detected by competitive solid phase ELISA.

Forty out of 54 consecutive cases of suspected AIHA were positive by one or more tests namely 14 DAT-tube, 19 microcolumn, 19 solid phase and 35 MS-DAT. Among the 14 DAT-tube positive cases, 11 were confirmed by all test, and 3 by one or more (1 microcolumn, 1 solid phase, and 1 MS-DAT), eluates were positive in 11, and the majority of patients (10/14) showed hemolytic anemia. As regards the 26 DAT-tube negative cases, 7 were positive in microcolumn and solid-phase (eluates positive in 2/8, panreactive), and 16 in MS-DAT, although in both groups anemia and hemolytic signs were less clear. Mitogen stimulation increased the amount of RBC-bound IgG in all groups, suggesting that MS-DAT could disclose a latent autoimmunity. Tube-negative/other methods positive cases included patients with B-CLL, myelodysplasia/aplasia, and thalassemia intermedia, in which autoimmune phenomena are more frequently observed than overt clinical autoimmune diseases. MS-DAT failed to detect anti-erythrocyte antibodies in half cases AIHA in clinical remission which still were tube-positive. Finally, MS-DAT was the only positive test in 10 cases of AIHA of difficult diagnosis, and mitogen stimulation allowed the identification of autoantibody specificity in culture supernatants of 2 cases which gave weak positive results in microcolumn/solid phase only.

We concluded that a battery of tests rather than a single test is recommended for the diagnosis of AIHA, depending on the specific clinical context: tube is still a good choice for first screening, microcolumn and solid-phase, which are the automated routine, should be confirmed by a positive eluate to diagnose AIHA, although positivity without a clinical equivalent may be taken into account as part of an autoimmune habitus. MS-DAT could be considered as an additional test for selected cases of difficult diagnosis.

No relevant conflicts of interest to declare.