Coombs test: usability, process, and read test results

Definition

What is that Coombs test?

Coombs test or Coombs test is a blood test or test that is done to find certain antibodies that attack red blood cells.

Normally, antibodies protect the body from germs that cause disease. However, antibodies sometimes make mistakes and attack healthy cells instead. That is why, this test is done to find out this.

There are two types Coombs test commonly done, namely:

1. Coombs test live (direct)

Live Coombs Test (direct) or also known as direct antiglobulin testing (DAT), involves a direct examination of the red blood cells found in a blood sample.

This procedure is performed by washing a blood sample that is collected in a saline solution to isolate the patient's red blood cells. Coombs test direct removes unbound antibodies that could confuse the results.

2. Coombs test indirect (indirect)

Indirect Coombs Test (indirect) or also known as indirect antiglobulin testing (IAT). This examination is done by checking the blood plasma. In contrast to DAT, this procedure is used to detect antibodies that are not bound to red blood cells, which may be present in the patient's serum.

When Coombs test done?

Quoted from the Stanford University website, the following is an explanation of when Coombs test necessary:

Coombs test

Coombs test indirect performed on a maternal blood sample as part of a prenatal laboratory test. This test looks for a list of antigens that can cause problems in the newborn or cause problems to the mother if a blood transfusion is needed.

Other than that, Coombs test indirect (indirect) is usually used to determine whether the donor's blood is suitable and can be used for the person who will receive it.

Warnings and Precautions

What should be known before receiving the Coombs test?

Newborns (of mothers who have negative rhesus blood) can have a direct Coombs test (direct) to check for antibodies against the baby's red blood cells.

If the test is positive, the baby may need a transfusion with appropriate blood to prevent anemia.

There are several factors or reasons that make the Coombs test results useless and cannot be used as a reference, including:

• Have received blood transfusions in the past
• Are pregnant for the last three months
• Using several drugs, such as cephalosporins, sulfa drugs, tuberculosis drugs, insulin, and tetracyclines

If you have this condition, tell your doctor for specific instructions. You should wear short-sleeved clothing to make it easier for the nurse to collect your blood sample.

Although it is rare, the Coombs test may present a number of risks. This is because the size of the veins and arteries of different people. Drawing blood from some people can be more difficult than drawing blood in others.

In rare cases, risk does Coombs test that you might experience, include:

• Fainting or dizziness
• Repeated punctures to find a vein
• Hematoma (buildup of blood under the skin)
• Excessive bleeding
• Infection (the risk that occurs when the skin breaks)

Process

What should be done before undergoing the Coombs test?

No special preparations have been made for this type of blood test. The doctor will ask you to drink a normal amount of water before doing blood tests.

This is a relatively safe procedure, so the risk is small or almost non-existent. You also don't need to fast before having this test.

You may have to stop using some medications before the test is done, but only if your doctor asks you to do so. Make sure you ask your doctor about this.

How is the Coombs test process?

In general, the process of drawing blood to perform this test is the same as taking a normal blood sample.

Your upper arm will be tied with an elastic band and the nurse will insert a needle in the crease of your elbow to collect a blood sample.

If the nurse is having trouble finding a vein, you may be given multiple injections. Later, the nurse will then collect your blood sample into a tube to be examined in the laboratory.

Because this test is often performed on babies who may have different antibodies in the blood than the mother, the nurse will use a small, sharp needle, known as a lancet. The point of injection or blood draw is usually at the heel of the baby's foot.

The collected blood will be placed into a glass tube, on a glass slide, or on a test strip.

What should I do after receiving the Coombs test?

Generally, you can start your normal activities immediately after taking this test. The pain you feel usually depends on the skills of the nurse, the condition of your veins, and your sensitivity.

After the blood is drawn, you should bandage and apply pressure to the injection site slowly.

Explanation of Test Results

What does the Coombs test result mean?

After being examined in the laboratory, you will get the results of the Coombs test. Here's the explanation.

1. Normal

A normal result means that there are no antibodies in your red blood cells. This is also known as a negative test.

• Live Coombs Test (direct)
  Negative: your blood does not have antibodies attached to erythrocytes
• Indirect Coombs test (indirect)
  Negative: your blood is compatible with the blood that will be received during the transfusion. Coombs test which states negative for rhesus factor (Rh antibody titer) in a pregnant woman indicates that there are no antibodies against her baby's rhesus positive blood (rhesus sensitization).

2. Abnormal

Your Coombs test results are called abnormal if they are positive. The following is the full explanation.

• Live Coombs Test (direct)
  A positive test result shows that you have antibodies that fight (destroy) your own red blood cells. This could be due to a transfusion of incompatible blood or it may be related to conditions such as hemolytic anemia or hemolytic disease of the baby (HDN).
• Indirect Coombs test (indirect)
  A positive test result means that your blood does not match the blood of a donor and you cannot accept blood donations from that person. If the Rh (rhesus) antibody titer test is positive in a woman who is pregnant or planning to become pregnant, it means that she has antibodies against Rh positive blood (also known as Rh sensitization) and will be tested early in pregnancy to check the baby's blood type. If the baby has Rhesus positive blood, the mother should be closely monitored throughout the pregnancy to prevent problems with the baby's red blood cells. If sensitization has not occurred, this can be prevented with an injection of Rh immunoglobulin.