Rh system is tested in presence of

• A. Rh negative
• B. Rh positive
• C. AB positive
• D. O negative

Answer: (B)

Rh typing determines whether the D antigen is present on red blood cells. The test uses anti-D reagent; if the D antigen is there, the antibodies bind and cause visible agglutination, which is read as Rh positive. If there’s no agglutination, it’s Rh negative. This is why the result is Rh positive when the Rh system is being tested in the presence of the D antigen—the defining feature of Rh positivity. AB positive and O negative are ABO/Rh reports that involve other antigens and aren’t what establishes Rh status.