How to Determine Blood Type

Blood group guess
Father O x mother O = son O
Father O x mother A = child A or O
Father O x mother B = child B or O
Father O x mother AB = child A or B
Father A x mother A = child A or O
Father A x mother B = child A, B, AB or O
Father A x mother AB = child A, B or AB
Father B x mother B = child B or O
Father B x mother AB = child A, B or AB
Father AB x mother AB = child A, B or AB
Blood types also include “Rh factor” (+ or -). If both parents have Rh- blood type (such as O- or AB-), you also have Rh- factor. If your parent has Rh+ factor, you won’t be able to tell if you have + or – factor without testing. ^[2]

Use a blood group test kit
Note that all at-home tests are less accurate than tests performed by a healthcare professional. Check the “Anti-A” and “Anti-B” tape for adhesion: Adhesion on Anti-A (on Anti-A only) means you have blood type A. Adhesion on Anti-B: you have blood type B. Stick on Anti-A and Anti-B: you are blood type AB.
Test the “Anti-D” tape: Adhesive: you are Rh positive. Add the ⁺ sign to your blood type. Non-adhesive: you are Rh negative. Add a ^– to your blood type.
Adhesive on contrp paper tape? If the contrp (plain paper) tape causes the blood to stick, or if you’re not sure which tape the blood is on, try a different card. ^[5]