1. Skip to Menu
  2. Skip to Content
  3. Skip to Footer

Direct Antiglobulin Test

The antiglobulin test is either direct (DAT) or indirect (IAT). Medical applications of the DAT and IAT are summarized in the following table.

Medical Applications of the Direct & Indirect Antiglobulin Tests

Direct Antiglobulin Test

Indirect Antiglobulin Test

Hemolytic disease of the newborn

Detection of unexpected antibodies in plasma

(Antibody screen)

Autoimmune hemolytic anemia

Compatibility testing

Drug induced red cell sensitization

Detection of some RBC antigens not demonstrable

by other techniques

Hemolytic transfusion reactions

 

The direct antiglobulin test (DAT) is performed to determine if a patient's red cells are coated in vivo with IgG or complement components. In the DAT, red cells are taken from the patient, washed to remove unbound IgG and then directly tested with antiiglobulin reagent (anti-IgG and/or anti-complement). If antibody is coating the patient’s red cells, they are agglutinated by antiglobulin. The DAT is extremely sensitive; it can detect as few as 100 IgG and 400 C3d molecules per red cell.

Approximately 1 in 9000 healthy persons has a positive direct antiglobulin test with no evidence of hemolysis. Some diseases may be associated with a positive DAT, even though the patient does not appear to be actively hemolyzing their red cells. Examples include chronic lymphocytic leukemia, multiple myeloma, systemic lupus erythematosis, infectious mononucleosis, mycoplasma infection, and AIDS. Different studies have reported that 0.3 to 1.5% of hospitalized patients have a positive DAT.

Autoimmune hemolytic anemia is classified as warm or cold autoantiobody types based on the temperatures at which the antibodies maximally react with red blood cells in vitro. Warm autoantibodies are more reactive at 37oC than at lower temperatures, whereas cold autoantibodies react optimally at 5oC and less strongly at higher temperatures.

Characteristic Serological Findings in Autoimmune Hemolytic Anemias

Type of AIHA

DAT Result

Antibody Screen

Antibody Specificity

Warm antibody

IgG, C3 or both

Positive in 55%

Nonspecific or Rh

Cold Agglutinin

C3 alone

Positive up to 30oC

Anti-I or i

Paroxysmal Cold Hemoglobinuria

C3 alone

Biphasic hemolysin

Anti- P

In warm autoimmune hemolytic anemia, RBCs may be coated with IgG, IgG and complement, or complement alone. IgG is found alone in about 60% of cases and in association with complement in about 30% of cases. In contrast, cold autoimmune hemolytic anemia is caused by complement-fixing IgM antibodies. In these cases, the direct antiglobulin test detects only complement.

The following table lists numerous drugs that have been associated with a positive DAT.

Medications Associated with a Positive Direct Antiglobulin Test

Acetaminophen

Fenoprofen

6-mercaptopurine

Sulbactam

Amoxicillin

Fludarabine

Methicillin

Sulindac

Amphotericin

Fluoroquinolones

Methotrexate

Sulfonamides

Ampicillin

Fluorouracil

Methyldopa

Sulfasalazide

Carbenicillin

Hydralazine

Metrizoate contrast

Tazobactam

Carbimazole

Hydrochlorothiazide

Nafcillin

Teicoplanin

Carboplatin

Ibuprofen

Norfloxacine

Temafloxacin

Cephalosporins

Insulin

Oxaliplatin

Teniposide

Chlordiazepoxide

Interferon

Penicillin G

Tetracycline

Chlorpromazine

Interleukin 2

Piperacillin

Ticarcillin

Chlorpropamide

Isoniazid

Probenacid

Tolbutamide

Cisplatin

Latamoxef

Quinidine

Tolmetin

Clavulanate

Levodopa

Quinine

Triamterene

Declofenac

Levofloxacin

Ranitidine

Zomepirac

Diphenylhydantoin

Mefenamic acid

Rifampicin

Zosyn

Erythromycin

Mefloquine

Streptokinase

Etodolac

Melphalan

Streptomycin

Drug induced hemolytic anemia is very rare. The incidence has been estimated to be one case per 1 million individuals. The most common cause of drug induced hemolytic anemia is the 2nd and 3rd generation cephalosporins. Of these, cefotetan appears to be the worst offender. The purine analogue, fludarabine, is used to treat chronic lymphocytic leukemia and produces a positive DAT is almost 35% of cases.

A DAT should be performed whenever there is:

  • A physician order
  • Hemolytic transfusion reaction investigation
  • Hemolytic disease of the newborn investigation
  • An antibody panel has a positive autocontrol
  • An unexpected positive antiglobulin crossmatch (on donor RBCs)

The strength of the direct antiglobulin test does not predict the biological activity of antibodies. For instance, some patients with a strongly positive direct antiglobulin test have little hemolysis, while other patients with weakly positive or negative direct antiglobulin test hemolyze extensively. Also, the strength of the direct antiglobulin test often does not change following treatment, even though the clinical condition greatly improves.

AddThis Social Bookmark Button

Stay Informed

Amazon Book

Our Sponsors

Login Form

Mobile Applications

iPad mini Horz Vert 300w

Get it for: iPhoneiPad

ClinLab Navigator Information

McAfee SECURE sites help keep you safe from identity theft, credit card fraud, spyware, spam, viruses and online scams
© 2015 ClinLab Navigator, LLC.