The essentials

The Coombs test, also called the antiglobulin test, looks for antibodies aimed at red blood cells. The direct test (DAT) checks whether antibodies are already stuck to your red cells; the indirect test (antibody screen) looks for antibodies circulating in your plasma, before a transfusion or during pregnancy. A normal result is negative. A positive result is a clue, not a diagnosis: it is read with your blood count and signs of red cell breakdown.

How do I read my Coombs test result?

The test does not give a number in units. The lab adds an antiglobulin reagent to red cells: if they clump together, the result is positive[1]. Here is a fictitious US report with a direct test and an antibody screen.

Fictitious example of a lab report line (United States format)
TestResultReference rangeFlag
Direct antiglobulin test (DAT), polyspecificPositive (2+)NegativeA
DAT, anti-IgGPositiveNegativeA
DAT, anti-C3dNegativeNegative-
Antibody screen (indirect antiglobulin test)NegativeNegative-
  1. Polyspecific DAT: the first screening line. Positive means antibodies or complement proteins coat your red cells[3].
  2. Strength (2+): labs grade how strong the clumping is. A stronger reaction means more antibody on the cells, but it does not always match how sick you are[3].
  3. Anti-IgG and anti-C3d lines: they tell which protein is attached. IgG points toward a warm autoimmune form; complement (C3d) alone points toward cold agglutinin disease[5].
  4. Antibody screen: a separate test of your plasma. Negative here means no circulating antibody against the test red cells was found[1].
  5. Flag A: abnormal. A positive DAT means something only next to your hemoglobin level and the markers of red cell breakdown.

A positive DAT, a plus sign or an antibody screen you do not understand? BloodSense explains every line of your report and helps you prepare questions for your doctor.

Get my Coombs result explained

What is the difference between the direct and indirect Coombs test?

Direct and indirect Coombs test side by side
Direct (DAT)Indirect (antibody screen)
What is testedYour own red cellsYour plasma or serum
What it findsAntibodies or complement already attached to your red cellsAntibodies circulating in your blood that could attack other red cells
Main usesUnexplained anemia or jaundice, suspected transfusion reaction, newborn jaundiceBefore a transfusion, during pregnancy

Your doctor may order a direct test if you have signs of anemia or jaundice (yellow skin or eyes)[1]. The indirect test is most often done to check whether you could react to a blood transfusion, and in pregnancy to look for antibodies against Rh-positive blood[1][2]. It is usually ordered with your blood type and Rh factor.

What is a normal Coombs test result?

A normal result is called negative: no clumping, and no antibodies to red blood cells were found[1]. There is no age or sex range, and your laboratory's report prevails.

How Coombs test results are reported
ResultWhat it meansSource
NegativeNormal: no antibody or complement detectedMedlinePlus[1]
Positive, with a strength (weak to strong)Antibodies or complement present; the strength reflects the amount, not the severityTesting.com[3]
Positive for IgG and/or C3dWhich protein coats the red cells; used to classify autoimmune hemolytic anemiaBarcellini 2015[5]

What does a positive direct Coombs test mean?

It means antibodies act against your red cells. The cells may be destroyed too early (hemolysis), but not always[1][3]. Possible causes, from the most frequent situations to the rarest:

  • Common No disease at all: a small share of healthy people have a positive DAT with no hemolysis[3], more often in older people[1]. In 152,564 blood donors, 16 had a positive DAT (about 1 in 10,000); published rates range from 1 in 1,000 to 1 in 36,000[7].
  • Common A newborn and mother with different blood groups: today the most frequent cause of hemolytic disease of the newborn is ABO incompatibility between a group O mother and her baby[3].
  • Possible Autoimmune hemolytic anemia: warm forms make up about 70% of cases (IgG), cold agglutinin disease about 20% (complement), mixed forms under 10%[5]. Your doctor will also look for a cause behind it[6]; see our guide to anemia symptoms and causes.
  • Possible A medicine, such as penicillin; the hemolysis usually settles once the drug is stopped[3]. Never stop a treatment on your own.
  • Possible Infections such as mycoplasma pneumonia or infectious mononucleosis[1].
  • Possible Autoimmune diseases, especially lupus[1].
  • Rare A transfusion reaction, for example after a poorly matched unit[1].
  • Rare Blood cancers such as chronic lymphocytic leukemia or lymphoma[1][3].

A positive DAT after a transfusion, an infection or a medicine may stay positive for 48 hours to 3 months; with an autoimmune condition it can stay positive for a long time[3]. The reverse also exists: some cases of autoimmune hemolytic anemia have a negative DAT and are often more difficult to treat[5].

Which other blood tests show that red cells are breaking down?

A Coombs test shows antibodies, not destruction itself. Hemolysis is shown by a raised reticulocyte count (young red cells), a high LDH, a low haptoglobin and a raised unconjugated bilirubin[5]. These markers can also change for other reasons[5]. Reticulocytes are not always high: they stay low in about 20% of adults with autoimmune hemolytic anemia[5]. Your complete blood count shows whether you are anemic at all.

Why is the indirect Coombs test done in pregnancy?

If you are Rh negative and your baby is Rh positive, your body can make antibodies against the baby's red cells. A first pregnancy is usually not affected, but a later Rh-positive baby can develop anemia and jaundice[2][9]. In the United States, the antibody screen is usually done in the first trimester and may be repeated at 28 weeks, when Rh-negative women receive Rh immune globulin[9]. About 15% of people in North America are Rh D negative. Immune globulin after birth cut the rate of immunization in at-risk pregnancies from about 13-16% to 0.5-1.8%, and adding a dose during pregnancy brought it to 0.14-0.2%[8]. Other blood groups can also cause antibodies; see how rare each blood type is.

After birth, a baby with significant jaundice may have a DAT together with both blood groups. The result is read according to the strength of the reaction and whether the mother received anti-D during pregnancy. A DAT on cord blood should not be used alone to predict severe jaundice[10].

What can affect a Coombs test, and do I need to fast?

No preparation or fasting is needed[1][2]. The DAT is a simple, widely used test, but it can give false-positive and false-negative results[4]. Before the draw, tell the lab or your doctor:

  • If you received Rh immune globulin (anti-D) during this pregnancy: it changes how your newborn's DAT is read[10].
  • If you had a transfusion in the last 3 months[3].
  • All the medicines you take, including recent antibiotics[3].
  • If you are treated with daratumumab for myeloma: it makes the antibody screen react with every test cell, and the blood bank uses a special method[11].

Practical tips are in our guide to what to expect at a blood draw.

When should I see a doctor about a positive Coombs test?

When to see a doctor

  • Emergency: call 911 for fever, chills, back pain or dark or red urine during or after a transfusion, severe shortness of breath, fainting, or a newborn who is very yellow, very sleepy or feeding poorly.
  • Within 24 to 48 hours if a positive DAT comes with new tiredness, paleness, yellow eyes or dark urine, or if you are pregnant and your antibody screen is positive.
  • At your next appointment if you feel well and a positive DAT was found by chance with a normal hemoglobin.

Questions to ask your doctor

  1. Is my result a direct test or an antibody screen?
  2. Are my hemoglobin, LDH, haptoglobin and bilirubin consistent with red cell breakdown?
  3. Is it IgG, complement, or both?
  4. Could one of my medicines explain this result?
  5. If I am pregnant: which antibody was found, and do I need extra monitoring?

Frequently asked questions

Is a positive Coombs test serious?

Not always. Some healthy people have a positive DAT with no hemolysis[3]. It matters when it comes with anemia and signs of red cell breakdown[5].

My baby's Coombs test is positive. What happens next?

The team checks the baby's bilirubin and blood count over the following hours and days, and reads the result with the mother's and baby's blood groups[10].

Is the Coombs test the same as a crossmatch?

Not exactly. The antibody screen looks for any antibody in your plasma before a transfusion; the crossmatch then checks your plasma against the donor blood chosen for you. Both are part of compatibility testing in the blood bank[1][11].

  1. MedlinePlus Medical Encyclopedia. Coombs test. US National Library of Medicine. medlineplus.gov (accessed October 30, 2026)
  2. Cleveland Clinic. Coombs Test: Purpose, Procedure & Results. my.clevelandclinic.org (accessed October 30, 2026)
  3. Testing.com. Direct Antiglobulin Test. testing.com (accessed October 30, 2026)
  4. Parker V, Tormey CA. The Direct Antiglobulin Test: Indications, Interpretation, and Pitfalls. Arch Pathol Lab Med. 2017;141(2):305-310. doi:10.5858/arpa.2015-0444-RS (accessed October 30, 2026)
  5. Barcellini W, Fattizzo B. Clinical Applications of Hemolytic Markers in the Differential Diagnosis and Management of Hemolytic Anemia. Dis Markers. 2015;2015:635670. doi:10.1155/2015/635670 (accessed October 30, 2026)
  6. Jäger U, Barcellini W, Broome CM, et al. Diagnosis and treatment of autoimmune hemolytic anemia in adults: recommendations from the First International Consensus Meeting. Blood Rev. 2020;41:100648. doi:10.1016/j.blre.2019.100648 (accessed October 30, 2026)
  7. Bharti J, Solanki A, Singh A, Agarwal M. Prevalence of direct antiglobulin test positive in whole blood donors: study at a tertiary blood center Northern India. Asian J Transfus Sci. 2024;18(2):237-241. doi:10.4103/ajts.ajts_188_23 (accessed October 30, 2026)
  8. American College of Obstetricians and Gynecologists. Practice Bulletin No. 181: Prevention of Rh D Alloimmunization. Obstet Gynecol. 2017;130(2):e57-e70. doi:10.1097/AOG.0000000000002232 (accessed October 30, 2026)
  9. American College of Obstetricians and Gynecologists. The Rh Factor: How It Can Affect Your Pregnancy. acog.org (accessed October 30, 2026)
  10. National Institute for Health and Care Excellence. Jaundice in newborn babies under 28 days (CG98), recommendations. nice.org.uk (accessed October 30, 2026)
  11. Chapuy CI, Nicholson RT, Aguad MD, et al. Resolving the daratumumab interference with blood compatibility testing. Transfusion. 2015;55(6 Pt 2):1545-1554. doi:10.1111/trf.13069 (accessed October 30, 2026)

This page is general information. It does not replace the advice of a doctor, who interprets your results with your symptoms, history and examination.