Home blood typing card kit, which uses the basic forward antibody method of blood haematology. In this method, blood samples are mixed with sera against A type blood, B type blood, and Rh positive blood. 100ml of such serum reagent is composed of 10ml of serum, 90ml of 6% dextran, and 2 drops of 5% heparin solution. The blood type is determined by examining which sample coagulates.

Each Eldon card has four panels covered with cellophane.

The first three panels are impregnated with dried monoclonal antibody sera anti-A, anti-B (for ABO grouping), and anti-D (for Rhesus grouping), respectively, and the last, control, panel does not contain antibodies:

Adding a few drops of water to each panel activates the antibody sera. Samples of blood (drawn from a fingertip or an ear lobe) can then be added spread across each test area. Within a few minutes, the results can be read:

Type A blood clots when mixed with anti-A serum.

Type B blood clots when mixed with anti-B serum.

Type AB blood clots when mixed with both anti-A and anti-B serums.

Type O blood does not clot when mixed with either anti-A or anti-B serum.

Rh-positive blood clots when mixed with anti-Rh serum.

Rh-negative blood does not clot when mixed with anti-Rh serum