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Blood Bank / Transfusion Medicine

Indirect Antiglobulin Test (IAT)

Indirect Antiglobulin Test (IAT) is a Blood Bank / Transfusion Medicine laboratory test reference in the LabPedia Medical Laboratory Library. Detects in vitro sensitization of red cells after incubation with plasma/serum and AHG; the serologic engine behind antibody screens, AHG crossmatches, and weak D testing.

Also known asIndirect Coombs test; Indirect AHG

Overview

The IAT incubates red cells with plasma/serum (± enhancement), washes away unbound immunoglobulin, and adds AHG to detect bound IgG (and sometimes complement, method-dependent).

Clinical Importance

Antibody detection and crossmatching at AHG phase

Weak D and selected antigen typing applications

Specimen Requirements

  • Specimen: EDTA plasma/cells and/or clotted serum as validated by the method
  • Tube: pink/lavender EDTA and/or red-top serum per SOP
  • Identity: strict patient identification at collection
  • Handling: separate cells and plasma/serum per method; store refrigerated within validated limits

Analytical Method

After 37 °C incubation (tube with LISS/PEG, or gel/solid-phase equivalents), cells are washed (tube) and AHG is added. Agglutination indicates IgG binding. Gel cards embed AHG in the matrix.

Instruments Used

Automated analyzers

  • Ortho Vision / Ortho Clinical Diagnostics automated immunohematology systems
  • Bio-Rad IH-1000 / IH-500 and related gel/column systems
  • Grifols Erytra / Wadiana automated blood typing systems
  • Immucor NEO / Echo luminescent immunohematology systems
  • Manual tube testing with centrifugation and macroscopic reading
  • Column agglutination (gel/bead) card systems
  • Solid-phase red cell adherence platforms

Manual methods

  • Manual tube testing with immediate-spin and AHG phases as applicable

Reference Values

Immunohematology interpretations follow institutional SOPs aligned with AABB Standards, ISBT terminology, and applicable CLSI / BSH guidance. Reagent lots, method (tube, gel, solid-phase), and patient history critically affect results; always verify against the performing laboratory’s current procedure and applicable standards edition.

Negative IAT expected when no reactive antibody is present under test conditions. Positive results are interpreted in the context of the specific application (screen, XM, typing).

Interpretation

Common Causes of Increased Results

  • Positive IAT; antibody bound in vitro; specificity depends on cells used

Common Causes of Decreased Results

  • Negative IAT; no detectable IgG binding under method conditions

Clinical Significance

  • Antibody screen and identification
  • AHG crossmatch
  • Weak D testing

Factors Affecting Results

Pre-analytical

  • Patient misidentification or unlabeled/mislabeled specimens
  • Wrong tube type or clotted EDTA specimen when plasma is required
  • Specimen older than institutional pretransfusion dating limits
  • IV fluid contamination or draw above an infusion

Analytical

  • Inadequate washing (tube) causing neutralization of AHG
  • Omitting IgG-coated check cells on negative tube IATs

Post-analytical

  • Transcription/LIS mapping errors of ABO/Rh or antibody results
  • Issuing products before resolving ABO discrepancies or positive screens per policy
  • Incomplete documentation of special requirements (antigen-negative, irradiated, etc.)

Advantages and Limitations

Advantages

  • Sensitive detection of most clinically significant IgG antibodies

Limitations

  • May miss IgM-only antibodies that do not react at AHG
  • Method-dependent sensitivity

Clinical Pearls

In tube IAT, check cells are not optional paperwork; they prove your negative wash actually worked.

Related Laboratory Tests

References

Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.

Textbooks

  • Cohn CS, Delaney M, Johnson ST, Katz LM, eds. Technical Manual. 21st ed. AABB; 2023.
  • Fung MK, Eder AF, Spitalnik SL, Westhoff CM, eds. Technical Manual. 20th ed. AABB; 2020.
  • Harmening DM. Modern Blood Banking & Transfusion Practices. 7th ed. F.A. Davis; 2019.
  • McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
  • Bain BJ, Bates I, Laffan MA, eds. Dacie and Lewis Practical Haematology (verify current edition). Blood transfusion chapters.

CLSI and Professional Guidelines

  • AABB. Standards for Blood Banks and Transfusion Services (verify current edition and institutional adoption).
  • U.S. Food and Drug Administration. Code of Federal Regulations Title 21 . Blood and Blood Components (verify current institutional adoption).
  • World Health Organization. Blood safety and availability / transfusion guidance (verify current WHO publication and institutional adoption).
  • Clinical and Laboratory Standards Institute. Related immunohematology and specimen identity standards (verify current documents and institutional adoption).
  • International Society of Blood Transfusion (ISBT). Blood group terminology and transfusion guidance (verify current ISBT publications).
  • British Society for Haematology (BSH). Guidelines for blood grouping, antibody testing, and transfusion practice (verify current BSH guideline editions).
  • Clinical and Laboratory Standards Institute. Immunohematology, specimen identification, and related transfusion laboratory documents (verify current CLSI editions).

WHO Publications

  • World Health Organization. Blood safety, availability, and clinical transfusion guidance (verify current WHO publication).

Frequently Asked Questions

Common questions about using this Indirect Antiglobulin Test (IAT) laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.

What is the Indirect Antiglobulin Test (IAT) laboratory test reference used for?

This Medical Laboratory Library page summarizes the clinical importance of Indirect Antiglobulin Test (IAT). Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.

Where can I find Indirect Antiglobulin Test (IAT) specimen requirements?

See the Specimen Requirements section on this page for specimen information related to Indirect Antiglobulin Test (IAT). Confirm collection details against your laboratory protocol.

Where are Indirect Antiglobulin Test (IAT) reference values listed?

See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.

How do I interpret Indirect Antiglobulin Test (IAT) results?

Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.

What analytical method is used for Indirect Antiglobulin Test (IAT)?

See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.

Are related laboratory tests linked from Indirect Antiglobulin Test (IAT)?

Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.

How can I continue learning after reading Indirect Antiglobulin Test (IAT)?

Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Blood Bank / Transfusion Medicine topic.

What are the clinical pearls for Indirect Antiglobulin Test (IAT)?

See the Clinical Pearls section for concise laboratory practice notes associated with Indirect Antiglobulin Test (IAT). Apply pearls alongside institutional protocols.

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