Red Cell Antibody Screen (Indirect Coombs)

A blood-bank test that checks whether your plasma has antibodies to red blood cell types you don't have. It is routine in pregnancy and before transfusions.

AI-verified against cited sources. Awaiting expert reviewAlso called IATLOINC 890-4

What it is

Your plasma can contain antibodies against red blood cell types that you don't have. They can form after a blood transfusion or a pregnancy. The antibody screen, also called the indirect Coombs test or indirect antiglobulin test, mixes your plasma with test red cells and looks for clumping. It is reported as negative or positive. If it is positive, the blood bank runs more tests to name the antibody. It is not the same as the direct Coombs test, which looks for antibodies already stuck to your own red cells.

Why it matters

Blood banks use the screen to find compatible blood for a transfusion. In pregnancy it is part of the 'type and screen' done at the first prenatal visit, because some antibodies can cross the placenta and affect the baby's red cells. Antibodies are uncommon: they turn up in about 1 to 2 in 100 first-trimester screens. Many are harmless, and when one does matter, finding it early lets the care team monitor and plan.

If it’s high

A positive screen means your plasma has an antibody that reacts with red cells. It does not say which antibody it is or whether it matters. The blood bank identifies it next. Some antibodies are harmless, and some can affect transfusions or pregnancy. In pregnancy, a positive screen after an Rh immune globulin injection is often passive anti-D from the medicine rather than a new antibody. That can be hard to tell apart, so earlier results and the timing of the injection matter.

Common causes

A past blood transfusion
A past pregnancy, when some of the baby's red cells got into your blood
Rh immune globulin given earlier in the pregnancy (passive anti-D)
Antibodies that don't cause problems, such as Lewis or P1 antibodies, which are not linked to disease in newborns
Antibodies against your own red cells (autoantibodies), which blood banks also look for when red cells may be breaking down early
Anti-CD38 antibody medicines used for multiple myeloma

What can help

Ask which antibody was found and whether your lab considers it clinically significant
If you are pregnant, ask how often the antibody will be rechecked and who will follow it
Ask how your result will be recorded so that any future care team or blood bank knows about it

What can affect your result

Recent pregnancy, transfusion, or an Rh immune globulin injection
Anti-CD38 antibody medicines used for multiple myeloma
The method and reagents the lab uses (tube, gel or solid-phase testing)
Timing: the result reflects the day of the draw, and new antibodies can appear later
Anti-CD38 antibody medicines used for multiple myeloma can make the screen react with every test cell, which can hide or mimic real antibodies. Tell the blood bank if you take one.
Rh immune globulin given during pregnancy leaves passive anti-D in your blood. It can show up as a positive screen and can be hard to tell apart from a new antibody, so a screen done before the injection is a useful baseline.
Your result only covers the day your blood was drawn. New antibodies can appear after a transfusion or after pregnancy-related bleeding or injury, which is why the screen is repeated at set times.

The result shows antibodies present on the day of the draw. New antibodies can form after a transfusion or after pregnancy-related bleeding.

When to talk to a clinician

A positive antibody screen is not an emergency by itself. If you are pregnant, tell your prenatal clinician soon so follow-up testing can be planned. If you are Rh negative and pregnant, tell your care team right away about vaginal bleeding, a hit to the belly or a pregnancy loss, because you may need repeat testing and treatment to prevent antibodies.

Questions you could ask

Is my result recorded so future care teams and blood banks can see it?
Which antibody was found, and does it matter for my pregnancy or for a transfusion?
How often will it be rechecked, and who will follow it?
Could an earlier injection or a medicine I take explain this result?

Questions people ask

Is the antibody screen the same as the Coombs test?

It is the indirect Coombs test. The direct Coombs test (direct antiglobulin test) is a different test that looks for antibodies already stuck to your own red blood cells.

My screen is positive. Does that mean something is wrong?

Not by itself. A positive screen means an antibody was found, and the blood bank then works out which one and whether it matters. Some are harmless, and in pregnancy a positive result can come from an Rh immune globulin injection. Your care team will explain the follow-up.

Why am I having this test again at 28 weeks?

If you are Rh negative, your care team usually repeats the screen at about 28 weeks to check that you have not made new antibodies. If you are Rh positive and your first screen was negative, no more routine screens are needed unless something like bleeding or an injury happens.

Show the science and sources

For clinicians and researchers

The antibody screen (indirect antiglobulin test) incubates the patient's serum or plasma with reagent red cells of known antigen types, then adds antihuman globulin and looks for agglutination or hemolysis. Methods include tube, gel and solid-phase; LOINC has a separate code for gel (75263-4). In pregnancy the screen looks for non-ABO antibodies such as anti-D, anti-Kell, anti-c, anti-E, anti-Jka, anti-Jkb, anti-Fya and anti-Fyb. Red cell antibodies are found in about 1% to 2% of first-trimester screens, and the antibodies most often linked with hemolytic disease of the fetus and newborn are anti-D, anti-Kell, anti-E and anti-c; anti-D, anti-c and anti-Kell are linked with severe disease, and anti-Kell can harm the fetus even at low titers. Lewis, I and P1 antibodies are not associated with HDFN (Canadian Family Physician 2020). Mayo Clinic Laboratories runs the screen (ABYSR) by hemagglutination on EDTA whole blood, with a reference result of 'Negative' and automatic reflex to antibody identification if positive; it lists pretransfusion testing, transfusion reactions and hemolytic anemia as uses, and detects allo- or autoantibodies. A positive screen leads to antibody identification (Mayo's ABIDR, hemagglutination, reference value 'Negative' with antibodies identified if positive), assessment of clinical significance and, when a significant antibody is found in a pregnancy, titration, usually every 2 to 4 weeks. Passive anti-D after Rh immune globulin is hard to separate from new alloanti-D, so a baseline before the injection helps (Canadian Family Physician 2020); Mayo notes its identification test is not useful for monitoring the effect of Rh immune globulin. Anti-CD38 therapies bind CD38 on red cells and cause panagglutination on the indirect antiglobulin test (Lancman 2018). This is not the direct antiglobulin test, which detects antibody already bound to the patient's own red cells.

LOINC 890-4 (primary), 75263-4. Specimen: serum-or-plasma.

Sources

Approach to red blood cell antibody testing during pregnancy: Answers to commonly asked questions, Canadian Family Physician (2020)
Coombs test, MedlinePlus Medical Encyclopedia, National Library of Medicine
The Rh Factor: How It Can Affect Your Pregnancy, American College of Obstetricians and Gynecologists (2022)
Blood Transfusion Management for Patients Treated With Anti-CD38 Monoclonal Antibodies, Frontiers in Immunology (2018)
Antibody Screen with Reflexed Antibody Identification, Blood (test ABYSR), Mayo Clinic Laboratories
Antibody Identification, Blood and Serum (test ABIDR), Mayo Clinic Laboratories

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.