How to Determine Your Blood Type: Positive and Negative Groups

Knowing your blood type is essential, especially if you frequently need blood transfusions or are planning to conceive. The ABO blood system categorizes blood types using the letters A, B, AB, and O. Your blood also carries the Rhesus factor, or Rh, which can be either positive or negative. You inherit both your blood type and Rh factor from your parents. To determine your Rh factor, learn about your parents' Rh status or undergo a blood test at a clinic.

Understand the factors that determine your Rh factor. The Rh factor is a protein found in your red blood cells, which you either inherit or don't inherit from your parents. If you have this protein, you're Rh positive. If not, you're Rh negative.

• People with the Rh factor are categorized as Rh positive, such as A+, B+, AB+, or O+. Those without the Rh factor are Rh negative, such as A-, B-, AB-, or O-.
• The majority of people have the Rh factor in their blood.

Check your health chart. If possible, request that your blood test includes an Rh factor analysis. Ask your doctor if they have your blood type on file. If you frequently need blood transfusions, your blood type may already be recorded, similar to when you donate blood.

• If your blood contains the Rh positive factor, you can receive both Rh+ and Rh- blood during a transfusion. However, if you have Rh- blood, you can only accept Rh- blood (unless in a life-threatening emergency, when Rh+ may be necessary).

Learn about your parents' Rh factors. Ask your parents about their blood types. You can determine your Rh factor by analyzing your parents' blood types. If both of your parents have Rh- blood types, it's likely you will have Rh- as well (with some exceptions mentioned below). If your mother has Rh- and your father has Rh+, or vice versa, you may have either Rh+ or Rh-. In this case, further testing by a doctor at a laboratory or hematology center is needed. It’s also worth noting that even if both parents are Rh+, you could still have Rh- blood.

• Because individuals with Rh+ blood can carry either two Rh+ genes (Rh+/Rh+) or one Rh+ gene and one Rh- gene (Rh+/Rh-), it’s possible for two Rh+ parents to have an Rh- child.

Ask your doctor about blood type testing. If your parents have different Rh factors, or if both parents have Rh+ blood types and you want to confirm your status, you can request a blood type test. The procedure is quick and minimally painful, and you can return home right after.

Undergo a blood test. Your doctor or nurse will clean the inside of your elbow or wrist with an antiseptic wipe. They will then locate the most accessible vein for drawing blood. After tying a tourniquet above your arm to stop blood flow, a needle will be inserted into your vein. The needle is usually connected to a syringe, which will extract your blood. Once enough blood has been collected, the needle will be removed and a sterile cotton ball will be pressed on the puncture site. Afterward, the area will be bandaged. The sample will be labeled and sent to the lab for analysis.

• For children, blood samples are usually taken from the back of the hand.
• If you feel faint, let the nurse know. They will assist you in lying down.
• You might feel a brief sting or discomfort when the needle is inserted. Afterward, you may experience some bruising at the puncture site. This discomfort usually fades quickly.

Check your blood sample. At the laboratory, a technician will test for the Rh factor in your blood sample. They will mix your blood with anti-Rh serum. If your cells clump together, you have Rh+ blood. If your cells do not clump together, you have Rh- blood.

• The lab may also test your blood type using the ABO system during this process.

Understand the importance of your results. Keep your blood type information in a secure place and share it with your emergency contact list. You will need this information if you ever require a blood transfusion or organ transplant. Additionally, knowing your Rh blood type is crucial if you're planning to become pregnant.

Be aware of pregnancy risks. If you are a woman with Rh- blood, your partner needs to undergo an Rh factor test. If you have Rh- blood and your partner has Rh+, you may encounter Rh incompatibility. This means if your baby inherits Rh+ blood from your partner, your antibodies may attack the baby's red blood cells, causing severe anemia and a potential threat to the baby’s life.

• Throughout pregnancy, if you have Rh- blood, you should have blood tests to check if your body is producing antibodies against Rh+. The first test occurs in the first trimester, and the second test happens at 28 weeks. If no antibodies are present, you will be given Rh immunoglobulin. This injection prevents your body from creating harmful antibodies against your baby.
• If your body produces antibodies against Rh+, you cannot receive Rh immunoglobulin. Instead, your doctor will closely monitor the baby’s development, and the baby may receive a blood transfusion before or after birth.
• Once the baby is born, the doctor can test the baby's Rh factor. If the baby shares the same Rh type as you, no further treatment is necessary. However, if you have Rh- blood and your baby has Rh+, you will need another dose of Rh immunoglobulin.