(4)Blood Test Compatibility

8/3/2019 (4)Blood Test Compatibility

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COMPATIBILITY TESTING

The purpose of pre-transfusioncompatibility testing is to PREVENThemolytic transfusion reaction


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DIFFERENT LEVELS OF COMPATIBILITY TESTING

Landsteiner,

1899

Landsteiner is noted for hisdevelopment in 1902 of themodern system of classification of bloodgroups from hisidentification of thepresence of agglutinins inthe blood


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ABO typing has two stages: one direct red blood cells -RBCs-typing using commercial antisera (anti-A, anti-B) and oneindirect typing utilizing plasma/serum and known - A and B -RBCs suspensions.

1. Direct ABO blood typing (or front grouping)

This test detects the presence of A and B antigens on RBCssurface by means of agglutination utilizing commercialantisera. It is a basic and simple test, it can be performed onfew drops of venous or capillary blood (i.e. obtained byfinger pricks) .

The RBCs are then examined for clumping (gross observation,gel suspension)

ABO TYPING

Antisera- serum containing antibodies


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Anti A Anti B Anti A Anti B

Anti A Anti B Anti A Anti B

A B

O AB
http://en.wikipedia.org/wiki/Image:ABO_blood_type.svg


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False positives Are rarely seen and they are essentially caused by the plasma

proteins when whole blood is used as specimen.These plasma-related agglutinations may be false or they may

be real agglutinations caused by auto-antibodies. These

apparently positive results turn generally negative whensaline-suspended RBCs are tested instead of whole blood.

Remember that auto-antibodies usually cause agglutination of all tested blood drops so beware of AB positive results ! Inthese cases the reverse typing will help to clarify the

situation .


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False negative

In theory it is possible if antisera are no longer working. Soantisera should be checked regularly with RBCs samples of known A and B type.

If reagents are working properly the only false negatives maybe due to the presence of very rare group A or B variants.

These may be also suspected because of discrepanciesbetween the direct typing and the reverse or indirect serum grouping.


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The H antigen is an essential precursor to the ABO blood group antigens

The H locus is located on chromosome 19. It contains 3 exons that span more than 5 kb of genomic DNA, and it encodes a fucosyltransferase that produces the H antigen on RBCs.


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This H substance is present in all RBCs, except those of hh (i.e.,Bombay blood group) and also produce antibody to both Aand B antigens, and are therefore compatible only with otherhh donors.

So, in the Bombay blood in serum or in reverse grouping thereis anti-A, anti-B, and anti-H.


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Reverse serum groupingThis test is used to confirm and must not substitute the front

grouping that remains the pillar of ABO typing.Reverse grouping helps to identify the rare cases of false

negative and false positive results.

The test puts in evidence the presence of naturally occurring Anti-A and Anti-B that are present after 6 months of life inall subjects that lack the reciprocal A/B antigen.

In order to perform the reverse test we need a saline 3-5%suspension of fresh RBCs of group A, B and O. The O type

RBCs suspension represents a negative control.Technique: 1) Mix 2 drops of serum or plasma under

investigation with one drop of each 3-5% RBCs suspension(group A, B and O); and 2) read for agglutination


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ABO TYPING

Back or reverse type with A and B cellsCommercially available A and B cells are added to

two tubes of plasma

AB B A O A B A B A B A B

Note: another sample of blood is usually added for Rh-D typing


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How do we know whether or not the host (or

recipient) has antibodies to minor bloodgroup antigens?

Add commercial RBCs with known importantminor antigens on their surface to host (orrecipient) plasma and centrifuge. Thenincubate at body temperature for 15-30

minutesThen add antiglobulin

Ex. of minor blood group [MNSs, Duffy (Fy) and Lewis (Le)].


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Antiglobulin reagent

Purification, concentrate and specific test


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Composition of antiglobulin reagent

1. Anti human globulins ( 1:32)2. Anti-complement (C3d, low titer

agglutinins to prevent false positive

from cold autoantibody

polyspecific

These natural cold autoantibodies occur at low titers, less than 1:64 measured at 4C, and have no activity athigher temperatures


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Classification of antiglobulin test

1. Direct antiglobulin test:To detect IgG bound on redcell

2. Indirect antiglobulin test:To detect free IgG in serum


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Direct antiglobulin test

Antihuman globulin (AHG)


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Antiglobulin test


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Indirect antiglobulin test


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If recipient antibodies have coatedcommercial RBC surfaces


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Method of antiglobulin test

Tube test

Gel test
http://2.bp.blogspot.com/_l3tH0cTgUmM/S7WZ1o4sc1I/AAAAAAAAAE0/0B_v2VxivuM/s1600/gruppi+3c.jpg


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Application of Direct Antiglobulin Test

(DAT)1. Hemolytic disease of the new born (HDN)2. Autoimmune hemolytic anemia (AIHA)

3. Drug -induced hemolytic anemia

4. Transfusion reaction hemolytic anemia


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Application of indirect antiglobulin test

1. Antibody identification2. Crossmatch / compatibility test3. Red cell typing4 . Investigate for HTR

Hemolytic transfusion reaction (HTR)


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Factors influence in antiglobulin test

Sensitization phase- Temperature- Reaction medium- Antigen-antibody ratio- Time

Washing phase: wash out unbound IgG


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False negative in antiglobulin test

1. Expired or out date serum, cells,reagents

2. Labile complement in aged plasma3. Improper time and temperature4. Washing:

- Inadequate

- longer time- low speed- non-continuous

5. Contamination in reagent serum


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False positive in antiglobulin test

1. Auto-aggregation of red cell2. Contamination of colloidal silica in saline3. Contamination of metallic ion in saline4. Contamination of detergent in container5. Longer time in centrifugation


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Hemolytic disease of the new born


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Rh incompatibility occurs when the mother'sblood type is Rh negative and her fetus' bloodtype is Rh positive (inherited the Rh-positiveantigen from the father)

If some of the fetus' blood passes into themother's blood stream, her body will produceantibodies in response

These antibodies could passback through the placenta andharm the fetus' red blood cells,causing mild to serious anemiain the fetus


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How to treat the HDN Before birth, options for treatment include intrauterine

transfusion or early induction of labor when pulmonary

maturity has been attained, fetal distress is present, or 35 to 37weeks of gestation have passed. The mother may also undergo

plasma exchange to reduce the circulating levels of antibody by

as much as 75%.

After birth, treatment depends on the severity of the condition,

but could include temperature stabilization and monitoring, phototherapy, transfusion with compatible packed red blood,

exchange transfusion with a blood type compatible with both

the infant and the mother, sodium bicarbonate for correction of

acidosis and/or assisted ventilation.

Rhesus-negative mothers who have had a pregnancy with/are pregnant with a rhesus-positive infant are given Rh immune

globulin (RhIG) at 28 weeks during pregnancy and within 72

hours after delivery to prevent sensitization to the D antigen. It

works by binding any fetal red cells with the D antigen before

the mother is able to produce an immune response and form

anti-D IgG.


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Whats new?

2007 Nature BiotechnologyUSA, Denmark, France, SwedenConvert blood types A, B, and ABto O, using bacterial glycosidaseenzymes to cleave the antigensfrom the RBC surface.Need D negative cells


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Red blood cell compatibility table

AB+

AB-B+

B-

A+

A-

O+

O-

AB+AB-B+B-A+A-O+O -

DonorRecipient
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Plasma compatibility table

O

B

A

AB

AB

B AO

DonorRecipient
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(4)Blood Test Compatibility

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