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If you’re receiving or donating an organ or stem cells, you’ll undergo some human leukocyte antigen (HLA) tests. These include HLA typing and HLA antibody tests. If the HLA type of a donor and a recipient are similar, the chances of the body rejecting the transplant are lower.

Mismatches between donor and recipient HLA will not exclude organ transplantation. However, the presence of antibodies to donor-mismatched HLA will.

Other names for HLA typing include histocompatibility testing and tissue typing. Here’s what you need to know about this important test.

What Is HLA?

The HLA is a group of genes within human DNA that makes special proteins called human leukocyte antigens (HLA). They are present on the surface of various cells throughout the body. The proteins signal to the immune system that a cell is part of the body and shouldn’t attack it.

Because your genes determine your HLA types, people genetically related to you are likelier to have similar HLA than someone unrelated to you. The more HLA genes people share in common, the more their HLA proteins will match.

Each person inherits half of their HLA genes from one parent and half from the other. This means siblings have a 25% chance of inheriting the exact same HLA genes from parents. If this happens, though, it makes them a perfect match for a stem cell or organ transplant.

Although your HLA type is less likely to fully match that of someone unrelated to you, it’s still possible. People can take an HLA test and add their information to a stem cell donation registry. If their HLA type matches the HLA type of someone in need, they may donate stem cells.

To be a live donor for kidney transplantation, people will need a comprehensive assessment by the transplant doctors.

What Is Anti-HLA Antibody Testing?

An anti-HLA antibody test checks whether the recipient has antibodies for the donor’s HLA proteins. The immune system makes antibodies to recognize and destroy specific invaders.

Just like you can develop antibodies for a virus, you can also make antibodies for an HLA protein on a donor’s cells. Your body may make these antibodies if exposed to that protein through a blood transfusion, pregnancy, or a previous transplant.

If you have too many antibodies for the HLA proteins in the donor’s tissues, your doctor may suggest looking for another match. If another match is unavailable, they may suggest medicines that reduce the anti-HLA antibodies in your blood before a transplant.

The HLA antibody test is also used to monitor the risk of rejection after organ transplantations. Once rejection occurs, the test is critical in assessing how well the medication treats rejections.

Is your HLA type the same as your blood type?

No, your HLA type is separate from your blood type. You may have the same blood type someone else does but a very different HLA type, and vice versa.

When Do You Need a Histocompatibility or HLA Test?

An organ transplant recipient needs to have HLA typing and screening for anti-HLA antibodies before and after an organ transplant, such as a kidney, lung, heart, or liver transplant. A stem cell transplant recipient needs to have HLA typing before transplantation.

When the donor is HLA-mismatched, the recipient may also need anti-HLA antibody tests.

Live donors need an HLA typing test to see whether they can donate a kidney, liver, or stem cells to someone they know. In other cases, such as kidney, heart, liver, or lung donations, HLA typing happens on deceased donors before the organs are retrieved. This ensures they go to a compatible recipient.

What Can I Expect with Histocompatibility or HLA Testing?

HLA testing usually involves a blood test. Some labs may test your HLA type using a sample taken from inside your mouth. An HLA-antibody test requires a small blood sample.

A doctor will take a small blood sample with a needle for the blood test, usually from the arm. You may feel a poke or sting for a few seconds. The sample-taking part of the test only takes a few minutes.

For the cheek swab test, a doctor will put a swab in your mouth and rub it against the inside of your cheek. The swab picks up some of the cells that line the inside of your mouth.

Results for nonurgent HLA tests may take several days to a week. When necessary, labs rush the HLA test on the donor to find a match within hours.

People usually get an HLA test when doctors determine they need a transplant. In addition to a person’s name and phone number, transplant waiting lists often include their HLA type and other important information.

Why is HLA Testing Necessary for Stem Cell Transplantation?

The degree of matching HLA genes in stem cell transplantation is important to avoid graft-versus-host disease (GVHD).

When the donated stem cells have matured into blood cells, they can attack your body’s cells. This is known as graft-versus-host disease because the donated cells identify your body’s cells as foreign.

Graft-versus-host disease can cause nausea, diarrhea, and skin problems. Severe cases can be fatal. This is why HLA typing is very important in stem-cell donation. The more closely the HLA type matches, the lower the risk of graft-versus-host disease.

Doctors treat graft-versus-host disease with immunosuppressive and steroid medications.