Finding the right tests…
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Finding the right tests…
Serology
The indirect Coombs test looks for antibodies floating free in your blood serum, before they have attached to any red blood cell - the opposite of what the direct version checks. A lab mixes your serum with red blood cells carrying a known set of surface markers, then adds a reagent that would clump the cells together if your serum contains an antibody against one of those markers. It is used most in two situations - to screen an Rh-negative pregnant woman's blood for antibodies against her baby's blood type, and to check that a unit of donor blood is compatible before a transfusion. Neither situation needs a bleeding symptom to justify testing.
This test screens serum for antibodies against red blood cell markers the person has never carried themselves - antibodies made only after past exposure, through pregnancy or a previous transfusion. It reports a plain positive or negative, and a positive result during pregnancy is usually followed by a titre, a measurement of how concentrated that antibody is. Before a transfusion, a positive result means the donor unit being tested needs to be swapped for one that will not react with the antibody found.
If you are Rh-negative and carrying an Rh-positive baby, small amounts of the baby's blood can cross into your bloodstream during pregnancy or delivery. Your immune system can respond by making antibodies against Rh-positive cells. This test looks for those antibodies early enough that a preventive injection - Rh immune globulin - can be given before your immune system builds a response that could affect a future pregnancy.
Donor blood is matched to your blood group, but group alone does not guarantee compatibility - a person can carry antibodies against markers separate from the main ABO and Rh groups, usually from an earlier pregnancy or transfusion. Running this test on your serum against a panel of test cells catches those less common antibodies before a transfusion, rather than after a reaction has already started.
- In pregnancy, a positive result is followed by a titre, to see how strong the antibody is and whether closer monitoring is needed - Before a transfusion, a positive result means the blood bank finds a matching unit that avoids the antibody - The specific antibody identified changes what happens next more than the fact that the test is positive at all
Your doctor or the blood bank explains what a positive result means for your specific situation, since the antibody identified matters more than a single positive or negative reading.
It means your serum contains an antibody against a red blood cell marker you don't carry yourself, most often related to Rh factor. Your doctor follows this up with a titre test to see how concentrated the antibody is and whether your pregnancy needs closer monitoring.
No, Rh-negative women are typically screened early in pregnancy and again later, since sensitization can develop at any point, particularly around delivery. Your doctor sets the schedule based on your specific history.
Not automatically. A positive result means an antibody is present, but whether it affects the baby depends on the antibody type, its concentration, and the baby's blood type, which is why further monitoring follows a positive result rather than an immediate conclusion.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
A blood type test identifies which ABO and Rh group your blood belongs to. The indirect Coombs test separately checks whether your serum contains antibodies against blood group markers, which a blood type test alone does not reveal.
Blood banks typically run an antibody screen, which is this test, as a standard part of preparing any transfusion, alongside blood typing and crossmatching. Your care team can explain exactly what's being checked before your specific transfusion.
The blood bank identifies the specific antibody and selects a donor unit that lacks the matching marker, so the transfusion doesn't trigger a reaction. This can take extra time, which is one reason antibody screening is done ahead of a planned transfusion whenever possible.