Definition

 When a particulate or insoluble antigen is mixed with its antibody in the presence of electrolytes at a suitable temperature and pH, the particles are clumped or agglutinated.

- Advantage: Agglutination is more sensitive than precipitation test and the clumps are better visualized and interpreted as compared to bands or floccules. Hence, agglutination tests are widely used even in today’s modern era of diagnosis

- Applications: Agglutination reactions are classified as direct, indirect (passive) and reverse passive agglutination reactions. All these agglutination tests are performed either on a slide, or in tube or in card or sometimes in microtiter plates.

Direct Agglutination Test

Here, the antigen directly agglutinates with the antibody.

Slide Agglutination

 It is usually performed to confirm the identification and serotyping of bacterial colonies grown in culture. It is also the method used for blood grouping and cross matching.

Bacterial colony is mixed with a drop of saline on a slide to form a uniform smooth milky white suspension

↓

To this, a drop of the antiserum (serum containing appropriate antibody) is added and the slide is shaken thoroughly (manually or by rotator) for few seconds

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A positive result is indicated by visible clumping with clearing of the suspension (Fig. 1)

or

If the milky white suspension remains unchanged, indicates a negative result (Fig. 1)

Fig1. slide agglutination test.

Tube Agglutination

This is a quantitative test done for estimating antibody in serum. The antibody titer can be estimated as the highest dilution of the serum which produces a visible agglutination.

Tube agglutination is routinely used for the serological diagnosis of various diseases, such as:

- Typhoid fever (Widal test): It detects antibodies against both H (flagellar) and O (somatic) antigens of Salmonella Typhi

* H antigen–antibody clumps appear as loose fluffy clumps

* antigen–antibody clumps appear as chalky white granular dense deposits.

- Acute brucellosis (Standard agglutination test)

- Coombs antiglobulin test

- Heterophile agglutination tests:

* Typhus fever (Weil Felix reaction)

* Infectious mononucleosis (Paul Bunnell test)

* Mycoplasma pneumonia (Cold agglutination test).

Microscopic Agglutination

 Here, the agglutination test is performed on a microtiter plate and the result is read under a microscope. The classical example is microscopic agglutination test (MAT) done for leptospirosis.

Indirect or Passive Agglutination Test (for Antibody Detection)

As agglutination test is more sensitive and better interpreted than precipitation test, attempt has been made to convert a precipitation reaction into an agglutination reaction. This is possible by coating the soluble antigen on the surface of a carrier molecule (e.g. RBC, latex or bentonite), so that the antibody binds to the coated antigen and agglutination takes place on the surface of the carrier molecule.

Indirect Hemagglutination Test (IHA)

 It is a passive agglutination test where RBCs are used as carrier molecules. IHA was used widely in the past, but is less popular at present.

Latex Agglutination Test (LAT) for Antibody Detection

Here, polystyrene latex particles (0.8–1 µm in diameter) are used as carrier molecules which are capable of adsorbing several types of antigens. For better interpretation of result, the test is performed on a black color card.

- Drop of patient’s serum (containing antibody) is added to a drop of latex solution coated with the antigen and the card is rotated for uniform mixing

- Positive result is indicated by formation of visible clumps (Fig. 2). LAT is one of the most widely used tests at present as it is very simple and rapid

- It is used for detection of ASO (antistreptolysin O antibody).

Fig2. Passive (latex) agglutination test.

Reverse Passive Agglutination Test (for Antigen Detection)

In this test, the antibody is coated on a carrier molecule which detects antigen in the patient’s serum.

- Reverse passive hemagglutination assay (RPHA): Here, the RBCs are used as carrier molecules. RPHA was used in the past for detection of hepatitis B surface antigen (HBsAg); now obsolete

- Latex agglutination test for antigen detection: It is used widely for detection of CRP (C reactive protein), RA (rheumatoid arthritis factor), capsular antigen detection in CSF (for pneumococcus, meningococcus and Cryptococcus) and streptococcal grouping

- Coagglutination test: Here, Staphylococcus aureus (protein A) acts as carrier molecule. This test was used in the past to detect antigen from clinical specimens; now obsolete.

hemagglutination Test

It refers to the agglutination tests that use RBCs as source of antigen. Hemagglutination tests are of two types: direct and indirect (or IHA, obsolete now).

Direct Hemagglutination Test

 Serum antibodies directly agglutinate with surface antigens of RBCs to produce a matt. Examples include:

- Paul Bunnell test: It employs sheep RBCs as antigens to detect Epstein-Barr virus antibodies in serum. The test is performed in tubes

- Cold agglutination test: It uses human RBCs as antigens to detect Mycoplasma antibodies in serum. Test is performed in tubes

- Blood grouping (ABO and Rh grouping)

- Coombs test or antiglobulin test: It is performed to diagnose Rh incompatibility by detecting Rh antibody from mother’s and baby’s serum

* Rh incompatibility is a condition when a Rh negative mother delivers a Rh positive baby (Rh Ag +ve). During birth, some Rh Ag +ve RBCs may pass from fetus to the maternal circulation and may induce Rh Ab formation in the mother, which may affect future Rh positive pregnancies

* Rh antibodies are incomplete or blocking antibodies of IgG type. They can cross placenta and bind to Rh Ag on fetal RBCs, but does not result in agglutination; instead, they block the sites on fetal RBCs

* This reaction can be visualized by Coombs test, which is carried out by adding Coombs reagent. It contains antibody to human IgG, which can bind to Fc portion of Rh Ab bound on RBCs, resulting in visible agglutination.

Technical Issues in Agglutination Reactions

Two main problems pertaining to agglutination are prozone phenomenon and blocking antibody; both can cause false-negative agglutination test.

- Prozone phenomenon: Serum containing excess antibodies may fail to agglutinate with its antigen. This can be obviated by serial dilution of the serum and testing the antigen with each dilution of the serum sample

- Blocking antibodies: They are incomplete IgG antibodies. When they bind to antigens, they themselves cannot produce a visible agglutination; however, they can block the sites on antigens, thus prevent binding of any other antibodies to the antigens. Such blocking antibodies may be detected by performing the test in hypertonic (4%) saline or more reliably by adding antiglobulin or Coombs reagent.

اخر الاخبار

اخبار العتبة العباسية المقدسة

خدمات فكرية وثقافية عديدة قدمها مركز مُلتقى القمر الثقافي لزائري الأربعين

إحياءً لذكرى زيارة الأربعين.. العتبة العباسية المقدسة تواصل إقامة مجلسها العزائي

عبر كاميرات تعمل بالذكاء الاصطناعي.. قسم الاتصالات يوضح تفاصيل جديدة حول آلية عدِّ زائري الأربعين

شعبة الخطابة الحسينية النسوية تواصل نشاطاتها الفكرية والثقافية في مجمع الشيخ الكليني

المزيد

الآخبار الصحية

حجم جزء محدد من الجسم يعكس الصحة العامة ومخاطر الأمراض

تفشي عدوى بكتيرية بفرنسا يحتمل ارتباطها بنوع من الجبن الطري

دراسة حديثة تكشف ما تفعله الشاشات بـ"قلوب الأطفال" !

متلازمة المبنى المريض.. هكذا يتحول تكييف الهواء إلى خطر صحي ؟؟

المزيد

الآخبار التكنلوجية

كيف تتعامل مع حرارة الطقس أثناء القيادة؟

لماذا يجب عليك إيقاف تكييف السيارة قبل إطفاء المحرك؟

دراسة تكشف سببا محتملا وراء زيادة خطر إصابة الأطفال بالتوحد

تشيلي.. العثور على متحجرة حيوان ثديي صغير من زمن الديناصورات

المزيد

مواضيع ذات صلة

protein C, protein S

prostate-specific antigen (PSA), prostate cancer gene 3 (PCA3), MI-prostate score (MiPS)

prolactin levels (PRLs)

Enzyme-Linked Immunosorbent Assay (ELISA)

Precipitation Reaction

Heparins and Fondaparinux

Activated Partial Thromboplastin Time (aPTT)

Prothrombin Time (PT)

Diagnosis of Community-Acquired Pneumonia

progesterone receptor assay (PR assay, PRA, PgR)

progesterone assay

pregnancy-associated plasma protein-A (PAPP-A)