Mechanisms involved in DAT-negative WAIHA
| 1. Erythrocyte-bound antibody below the limit of detection of standard DAT |
| Erythrocytes from healthy individuals have up to 35 molecules of IgG bound to their surface.Standard DAT can detect >300-500 bound IgG molecules.WAIHA can occur with as few as 70-434 bound IgG molecules. |
| 2. Low-affinity IgG antibodies |
| Loosely bound antibodies are dislodged during the washing of erythrocytes or when samples are left standing at room temperature. |
| 3. IgA antibodies |
| IgA antibodies may trigger phagocytosis and antibody-dependent cell cytotoxicity, resulting in hemolysis.Standard anti–human globulin reagents do not have anti-IgA activity, as most polyspecific reagents contain a mixture of monoclonal anti-IgG and anti-C3d. |
| 4. Warm-reacting IgM and monomeric IgM antibodies |
| IgM antibodies reacting at warm temperatures and monomeric IgM may not fix complement.Standard anti–human globulin reagents do not detect IgM. However, these antibodies will detect C3d if the IgM antibody fixes complement. |
| 1. Erythrocyte-bound antibody below the limit of detection of standard DAT |
| Erythrocytes from healthy individuals have up to 35 molecules of IgG bound to their surface.Standard DAT can detect >300-500 bound IgG molecules.WAIHA can occur with as few as 70-434 bound IgG molecules. |
| 2. Low-affinity IgG antibodies |
| Loosely bound antibodies are dislodged during the washing of erythrocytes or when samples are left standing at room temperature. |
| 3. IgA antibodies |
| IgA antibodies may trigger phagocytosis and antibody-dependent cell cytotoxicity, resulting in hemolysis.Standard anti–human globulin reagents do not have anti-IgA activity, as most polyspecific reagents contain a mixture of monoclonal anti-IgG and anti-C3d. |
| 4. Warm-reacting IgM and monomeric IgM antibodies |
| IgM antibodies reacting at warm temperatures and monomeric IgM may not fix complement.Standard anti–human globulin reagents do not detect IgM. However, these antibodies will detect C3d if the IgM antibody fixes complement. |