The direct antiglobulin test commonly incorporates which reagent to detect coating on red cells?

• A. Monospecific anti-IgG only
• B. Complement components only
• C. Polyspecific antihuman globulin
• D. Monospecific anti-C3d only

Answer: (C)

The direct antiglobulin test detects antibodies or complement that are already bound to red cells in the patient. To reveal this coating, an antiglobulin reagent is added. A polyspecific antihuman globulin contains antibodies that recognize both human IgG and C3d (a complement component). Because red cells can be coated with either IgG or complement (C3d), using the polyspecific reagent catches either type of coating, increasing the test’s sensitivity. Monospecific reagents that target only IgG or only C3d could miss one form of coating, leading to a false negative. In practice, polyspecific AHG is used to maximize the chance of detecting immune coating on red cells.