Understanding the Lupus Coombs Test: Know your labs! (October 2024 Update)

posted in Diagnosing Lupus on June 11, 2024 by

Gavin Abson

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The Direct Coombs test is also known as the direct Coombs antibody test and the direct antiglobulin test (DAT). The Coombs test (pronounced like Kooms test) is a pivotal diagnostic tool in lupus diagnostics. This test plays a crucial role in identifying the presence of antibodies that target red blood cells. A positive result can provide valuable insights into conditions such as autoimmune hemolytic anemia commonly associated with lupus.

Like other labs seen in lupus, like anti-SSA, chromatin antibody, antinuclear antibody (ANA), anti-RNP, and urine tests, I (Don Thomas, MD) encourage all lupus patients to get copies of their labs and doctors’ notes. See what labs are abnormal and that are part of your lupus. Read about them to understand how they are important in your case. In the case of the direct Coombs antibody test, this test can help diagnose systemic lupus erythematosus. A positive Coombs test may also increase the risk for a type of anemia called autoimmune hemolytic anemia. Read on…

October 2024 Update

Understand more about antinuclear antibodies: The medical newspaper, The Rheumatologist, published my article about “A Practical Guide to Autoantibody Testing in Rheumatic Diseases.” Though it is written for healthcare providers, it gives lots of interesting information about these tests.

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This blog post article was edited and contributed to by Donald Thomas, MD; author of “The Lupus Encyclopedia.” Parts of this blog post come from “The Lupus Encyclopedia: A Comprehensive Guide for Patients and Health Care Providers, edition 2.“

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Understanding the Lupus Coombs Test

The  Coombs test involves collecting a blood sample to detect antibodies bound to the surface of red blood cells. In a laboratory setting, technicians perform this test using specific reagents to identify immunoglobulins.

Diagnostic Significance in Lupus

The test holds diagnostic significance in identifying immune-mediated hemolytic anemia (or autoimmune hemolytic anemia). This condition occurs when the immune system mistakenly attacks and destroys its own red blood cells.

However, people with systemic lupus erythematosus (SLE) are more likely to have a positive direct Coombs test in the absence of hemolytic anemia than people who have other autoimmune diseases. Therefore, a positive direct Coombs antibody test became a part of the SLE classification criteria in 2012. Lupus experts developed the classification criteria for research purposes. However, most rheumatologists also use them as a guide in diagnosing SLE patients. Consequently, the test aids in confirming lupus diagnosis and assessing the severity of associated complications. A 2018 study suggested that SLE patients who are positive for the direct Coombs test are more likely to have more severe disease than SLE patients who are Coombs negative.

Conducting the Lupus Coombs Test

Typically, a healthcare provider draws a blood sample from a vein in the patient’s arm to perform the test. The sample then goes to a laboratory where technicians process it to detect the presence of immunoglobulins attached to the surface of red blood cells.

Interpreting Lupus Coombs Test Results

Lupus Coombs Test and Autoimmune Hemolytic Anemia

A positive test result indicates the presence of antibodies on the surface of red blood cells. In the setting of hemolytic anemia, a positive result suggests autoimmune hemolytic anemia. Autoimmune hemolytic anemia can occur by itself or it may exist as one complication in someone who has systemic lupus erythematosus. Distinguishing this type of anemia from other types (like anemia of inflammation, anemia of chronic disease, or iron deficiency) is important because it needs to be treated with drugs that suppress the immune system and keep the immune system from attacking its own red blood cells.

Lupus Coombs Test Can Help Diagnosis Systemic Lupus Erythematosus

A positive direct Coombs antibody test is seen much more commonly in people with systemic lupus erythematosus (SLE) than those with other systemic autoimmune diseases. Therefore, a positive Coombs test became one of the SLICC SLE Classification Criteria in 2012. A positive result can support a diagnosis of possible SLE in people with symptoms seen in SLE. Further investigations are often conducted, including clinical assessments and additional laboratory tests.

Although having a positive direct Coombs antibody test in SLE increases a person’s risk for autoimmune hemolytic anemia, I (Don Thomas, MD) have rarely seen this occur (only one patient from 1993-2024). I suspect this most likely involves treating the SLE patient well. Using hydroxychloroquine and other therapies (like UV light protection and vitamin D) to calm down the immune system most likely reduce this risk.

Healthcare professionals involved in diagnosing and managing lupus must understand the Lupus Coombs test. This diagnostic tool is critical in identifying autoimmune complications, guiding treatment decisions, and improving patient outcomes.

Understand more about antinuclear antibodies

The medical newspaper, The Rheumatologist, published my article about “A Practical Guide to Autoantibody Testing in Rheumatic Diseases.” Though it is written for healthcare providers, it gives lots of interesting information about these tests.

For more in-depth information on Understanding the Lupus Coombs Test: Know your labs! (October 2024 Update):

Read more in The Lupus Encyclopedia, edition 2

Look up your symptoms, conditions, and medications in the Index of The Lupus Encyclopedia

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