Coombs' Antiglobulin, Direct

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Coombs’ Antiglobulin, Direct

Synonym/acronym: Direct antiglobulin testing (DAT).

Common use

To detect associated conditions or drug therapies that can result in cell hemolysis, such as found in hemolytic disease of newborns, and hemolytic transfusion reactions.


Serum (1 mL) collected in a red-top tube and whole blood (1 mL) collected in a lavender-top (EDTA) tube.

Normal findings

(Method: Agglutination) Negative (no agglutination).


Direct antiglobulin testing (DAT) detects in vivo antibody sensitization of red blood cells (RBCs). Immunoglobulin G (IgG) produced in certain disease states or in response to certain drugs can coat the surface of RBCs, resulting in cellular damage and hemolysis. When DAT is performed, RBCs are taken from the patient’s blood sample, washed with saline to remove residual globulins, and mixed with anti–human globulin reagent. If the anti–human globulin reagent causes agglutination of the patient’s RBCs, specific antiglobulin reagents can be used to determine whether the patient’s RBCs are coated with IgG, complement, or both. (See monograph titled “Blood Groups and Antibodies” and Effects of Natural Products on Laboratory Values online at DavisPlus for more information regarding transfusion reactions.)

This procedure is contraindicated for



  • Detect autoimmune hemolytic anemia or hemolytic disease of the newborn
  • Evaluate suspected drug-induced hemolytic anemia
  • Evaluate transfusion reaction

Potential diagnosis

Positive findings in:

  • Antibodies formed during these circumstances or conditions attach to the patient’s RBCs, and hemolysis occurs. Agglutination is graded from 1+ to 4+ in manual testing systems; with 4+ being the strongest degree of agglutination. Automated testing systems are capable of reporting 1+ to 4+ graded results, or providing images of the tested material so laboratory professionals can interpret the results, or providing computer assisted interpretation of the test results as positive or negative findings.

  • Anemia (autoimmune hemolytic, drug-induced)
  • Hemolytic disease of the newborn (related to ABO or Rh incompatibility)
  • Infectious mononucleosis
  • Lymphomas
  • Mycoplasma pneumonia
  • Paroxysmal cold hemoglobinuria (idiopathic or disease related)
  • Passively acquired antibodies from plasma products
  • Post–cardiac vascular surgery (increased incidence of positive DAT has been reported in patients following cardiac surgery, possibly related to mechanical RBC destruction while the patient is on cardiac bypass)
  • Systemic lupus erythematosus and other connective tissue immune disorders
  • Transfusion reactions (related to blood incompatibility)
Samples in which sensitization of erythrocytes has not occurred

Critical findings


Interfering factors

  • Drugs and substances that may cause a positive DAT include acetaminophen, aminopyrine, aminosalicylic acid, ampicillin, antihistamines, aztreonam, cephalosporins, chlorinated hydrocarbon insecticides, chlorpromazine, chlorpropamide, cisplatin, clonidine, dipyrone, ethosuximide, fenfluramine, hydralazine, hydrochlorothiazide, ibuprofen, insulin, isoniazid, levodopa, mefenamic acid, melphalan, methadone, methicillin, methyldopa, moxalactam, penicillin, phenytoin, probenecid, procainamide, quinidine, quinine, rifampin, stibophen, streptomycin, sulfonamides, and tetracycline.
  • Wharton’s jelly may cause a false-positive DAT.
  • Cold agglutinins and large amounts of paraproteins in the specimen may cause false-positive results.
  • Newborns’ cells may give negative results in ABO hemolytic disease.
  • Tube methods for DAT are less sensitive than gel methods, and false-negative findings are possible in cases where weak, incompletely developed antigen sites on newborns’ RBCs may not allow detectable amounts of anti-A and/or anti-B to bind to the RBC membrane. Neonates who have received multiple intrauterine transfusions of antigen-negative (group O) cells may also have a negative DAT because the results represent circulating donated red blood cells rather than the neonate’s native red blood cells.

Nursing Implications and Procedure

Potential nursing problems

ProblemSigns & SymptomsInterventions
Injury risk (Related to Rh incompatibility; blood incompatibility)Jaundice in newborn; infant cardiac stress (heart failure); infant death Administer prescribed Rh-immune immunoglobulin to mother; obtain maternal blood type and crossmatch; use bilirubin light for newborn; use infant treatment with prescribed erythropoietin and iron supplements; administer prescribed blood transfusion to infant; follow blood transfusion guidelines; monitor degree of jaundice and associated laboratory results (bilirubin); monitor HGB/HCT
Fear (Related to possible loss of newly born child; long-term effects of elevated bilirubin)Expression of fear; preoccupation with fear; increased tension; parental complaints of diarrhea, nausea; parental expressions of fatigue or insomnia; crying; withdrawal; panic attacks Access social services; provide specific and culturally appropriate education; assist the patient and family to recognize effective coping strategies; assist the patient to acknowledge fear; provide a safe environment to decease fear; explore cultural influences that may enhance fear; utilize therapeutic touch as appropriate to decrease fear
Gas exchange (Related to destruction of red cells secondary to maternal-child Rh incompatibility)Shortness of breath; orthopnea; cyanosis; increased heart rate; increased respiratory rate; use of respiratory accessory muscles Auscultate and trend breath sounds; use pulse oximetry to monitor oxygenation; administer oxygen as ordered; collaborate with physician to consider intubation and/or mechanical ventilation; elevate the infant’s head; administer ordered blood or blood products; monitor HGB/HCT


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient/parent this test can assist in assessing for disorders that break down red blood cells.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s hematopoietic system as well as results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture. If a cord sample is to be taken from a newborn, inform parents that the sample will be obtained at the time of delivery and will not result in blood loss to the infant.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • There are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications:
  • Acute hemolytic reactions can be immediate and life threatening for patients of any age. Chronic hemolytic anemia is also a significant condition that requires timely identification of the problem in order to treat the condition.

  • Assess the newborn’s bilirubin and hematocrit levels. Increased bilirubin and decreased hematocrit may be indicative of RBC breakdown. Kernicterus, or deposition of bilirubin in the brain, is a serious and significant development that can lead to permanent brain damage or death.

  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture. Cord specimens are obtained by inserting a needle attached to a syringe into the umbilical vein. The specimen is drawn into the syringe and gently expressed into the appropriate collection container.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Recognize anxiety related to test results, and inform the postpartum patient of the implications of positive test results in cord blood; also assess newborn’s bilirubin and hematocrit levels. The results may indicate the need for immediate exchange transfusion of fresh whole blood that has been typed and crossmatched with the mother’s serum in order to identify the presence of unusual antibodies. Observation of the neonatal patient, especially for the development of jaundice, is an important way to identify a hemolytic process. Facilities not equipped for neonatal exchange transfusion may elect to transfer the neonate to a facility where the appropriate level of care can be provided. Hand-Off communication is a standardized approach to sharing information in an effort to minimize the risk of error or injury during transition between caregivers. Use of the SBAR-R format (situation, background, assessment, recommendation, and read-back) may be used as a communication tool to ensure mutual understanding of the clinical situation.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.
  • Patient Education

    • Inform the postpartum patient of the implications of positive test results in cord blood.
    • Prepare the newborn for exchange transfusion, on medical direction.
    • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP.
    • Answer any questions or address any concerns voiced by the patient or family.
  • Expected Patient Outcomes

    • Knowledge
    • Parents state their understanding of the purpose for the recommended infant blood transfusion.
    • Mother states her understanding of the purpose of Rh-immune immunoglobulin injection in relation to future pregnancies.
    • Skills
    • Parents demonstrate proficiency in placing the infant under the bilirubin light and adhering to identified precautions.
    • Parents demonstrate proficiency in administering prescribed iron supplements to infant.
    • Attitude
    • Complies with the request to bring the infant in for bilirubin blood checks as designated by the HCP
    • Complies with the recommendation to receive Rh-immune immunoglobulin

Related Monographs

  • Related tests include bilirubin, blood groups and antibodies, CBC hematocrit, CBC hemoglobin, Coombs’ indirect antiglobulin (IAT), Ham’s test, and haptoglobin.
  • Refer to Effects of Natural Products on Laboratory Values online at DavisPlus at the end of the book for further information regarding laboratory studies used in the investigation of transfusion reactions, findings, and potential nursing interventions associated with types of transfusion reactions.
  • Refer to the Hematopoietic System table at the end of the book for related tests by body system.
Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners
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