Direct Coombs Test

Anemia

Report in 4Hrs

At Home

No Fasting Required

Details

It is primarily used to diagnose immune-mediated hemolytic anemia, which occurs when the immune system attacks its own red blood cells

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Direct Coombs Test - Comprehensive Information Guide

Section 1: Why is it done?
- Test Purpose: Detects antibodies and complement proteins attached to the surface of red blood cells (RBCs), indicating immune-mediated destruction of these cells
- Primary Indications: Evaluation of hemolytic anemia, investigation of jaundice in newborns, assessment of transfusion reactions, monitoring patients with autoimmune hemolytic anemia (AIHA)
- Clinical Scenarios: Performed when patients present with unexplained anemia, fever, dark urine, pallor, or jaundice; also used pre- and post-transfusion; ordered during pregnancy to screen for hemolytic disease of the newborn
Section 2: Normal Range
- Normal Result: NEGATIVE (or 0 IgG molecules per RBC)
- Reference Range Interpretation: Measured in antiglobulin units; negative indicates no detectable antibodies or complement on RBC surface; weakly positive (1+ to 2+) may occasionally be seen in normal individuals
- Units of Measurement: Graded on scale from 0 (negative) to 4+ (strongly positive); expressed as IgG molecules per RBC or as semi-quantitative titer
- Negative vs. Abnormal: Negative result suggests absence of immune-mediated RBC destruction; any positive result (1+ or greater) is abnormal and warrants clinical correlation
Section 3: Interpretation
- Negative Result (0): No antibodies or complement bound to RBCs; excludes immune-mediated hemolysis; rules out AIHA, hemolytic disease of newborn (HDN), and acute transfusion reactions in most cases
- Weakly Positive (1+ to 2+): Light to moderate coating of antibodies/complement; suggests mild immune sensitization; may be clinically insignificant or indicate early/resolving hemolysis; requires clinical context
- Moderately Positive (3+): Significant antibody coating; strongly suggestive of active immune-mediated RBC destruction; associated with symptomatic hemolytic anemia
- Strongly Positive (4+): Heavy antibody/complement coating; indicates severe immune-mediated hemolysis; associated with rapid RBC destruction and significant clinical symptoms
- IgG vs. IgM vs. Complement Patterns: IgG positivity suggests warm-type AIHA or HDN; IgM positivity suggests cold agglutinin disease or drug-induced hemolysis; complement (C3) positivity indicates classical pathway activation
- Factors Affecting Results: Recent transfusions, medications (methyldopa, penicillins, NSAIDs), infections, autoimmune diseases, lymphoproliferative disorders, pregnancy, and recent vaccination may influence results
Section 4: Associated Organs
- Primary Organ Systems: Hematologic system (blood/bone marrow); immune system; potentially liver and spleen (involved in RBC removal)
- Associated Diseases and Conditions: Autoimmune hemolytic anemia (warm and cold types); hemolytic disease of the newborn; transfusion reactions; drug-induced hemolysis; secondary hemolysis from systemic lupus erythematosus, lymphomas, leukemias, infectious mononucleosis, and other infections
- Clinical Complications: Severe anemia leading to hypoxia and tissue damage; acute kidney injury from hemoglobinuria; thrombosis from hemolysis; congestive heart failure from chronic compensatory responses; kernicterus in severe neonatal jaundice
- Diagnostic Value: Essential for confirming immune-mediated RBC destruction; positive result provides objective evidence of hemolysis mechanism and guides treatment decisions
Section 5: Follow-up Tests
- Confirmatory and Complementary Tests: Complete blood count (CBC) to assess degree of anemia; reticulocyte count to evaluate bone marrow response; peripheral blood smear for spherocytes and polychromasia
- Hemolysis Markers: Indirect bilirubin, lactate dehydrogenase (LDH), haptoglobin levels, urobilinogen, and hemoglobinuria testing
- Antibody Identification: Indirect Coombs test (Indirect Antiglobulin Test - IAT) to identify specific antibodies in serum; blood typing and cross-matching for transfusions
- Additional Workup: Cold agglutinin titer for suspected cold-type AIHA; direct antiglobulin test with anti-IgG and anti-C3 components; drug testing if drug-induced hemolysis suspected
- Monitoring Frequency: Repeat DAT after 2-4 weeks to assess treatment response; periodic monitoring (monthly) in chronic AIHA patients; pre-transfusion repeat testing
- Etiology Investigation: ANA for autoimmune disease; viral serology; imaging studies; bone marrow biopsy if lymphoproliferative disorder suspected
Section 6: Fasting Required?
- Fasting Requirement: NO - Fasting is not required for the Direct Coombs Test
- Patient Preparation: No special dietary restrictions; patient may eat and drink normally; no overnight fasting needed
- Sample Collection Timing: Test can be performed at any time of day; no time-of-day restrictions; STAT testing available if clinically urgent
- Medication Considerations: Continue all current medications including corticosteroids, immunosuppressants, and antibiotics; do NOT discontinue medications without physician approval; medications known to cause hemolysis should be documented
- Pre-Test Instructions: Inform laboratory of recent transfusions; report all current medications; notify staff of fever or acute symptoms; avoid strenuous exercise immediately before collection; stay hydrated
- Special Circumstances: For cold agglutinin disease patients, samples should be kept warm (37°C) during transport; inform laboratory if patient is hypothermic; priority handling for transfusion-related urgent testing

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