TWO CAS

            

                       

E REPORTD

      

TS OF RARDURING RO

RE WEAK ‘OUTINE TE

  

‘B’ SUBGRESTING 

ROUP DETECTED

Case Report

ABO system of blood groups forms the backbone oftransfusion medicine. However, apart from the usual A, B,AB and O groups, there also exist many variantphenotypes. The mechanisms underlying unusual bloodgroup expressions are not very well understood, althoughdecreased activity of the enzyme transferase, which areresponsible for the conversion of precursor substance H toA substance of blood group A (N-acetylgalactosaminyl-transferase) or to B substance of blood group B(galactosyl-transferase) have been postulated. Otherpossibilities, such as secondary decomposition of theblood group substances by a putative glycosidase anddecrease in concentration of the sugar donor (i.e., UDP-Ga1NAc and UDP-Gal) are also conceivable [1-4].

Variants of Type B blood, with weak expression of theB antigen, have been previously described and are knownto be rare. Race and Sanger [5] have divided them intothree subgroups according to the presence or absence of Bsubstance in the saliva and the presence or absence of anti-B in the serum. More recently, Salmon and colleagues [6]have used red cell agglutination, in conjunction with theguidelines proposed by Race and Sanger, to define fourweak B variant subgroups which were fairly similar tothose described for blood group A i.e., B3, Bx, Bm and Bel. In addition a category of Bw was incorporated for casesthat could not be classified into either of the categories. Inanother classification Lopez, et al [7] described 3 classesnamely B60, B20 and B0, based on mean percentageagglutination with anti-B.

B3: This subgroup is characterized by Mixed Field

Haemagglutination with anti-B and anti-AB and theabsence of anti B in the serum. B antigen is present in thesaliva normally [8].

Bx: This rare subgroup of B shows weak reaction withanti B and anti AB, the serum contains weak anti B andsaliva of Bx secretors contains some B substance [8].

Bm: In individuals with Bm subgroup, the B antigenrequires highly sensitive techniques for detection. Thesewould include adsorption and elution techniques. Noreaction is obtained with anti B or anti AB. Secretion of Bsubstance in saliva is fairly normal [8].

Bel: These cells do not show agglutination with anti A,or anti AB and no B substance is detected in saliva of Belsecretors. Anti B may be detected in plasma [8].

CASE REPORTS

We present two similar cases of rare B subgroupsidentified at our department within a span of one week.

Case 1

This was 35 year old male, who came for a regularhealth check at our hospital. His sample for ABO and Rhgrouping was received at our department. This wasperformed on the fully automated immunohematologyanalyzer (Galileo; Immucor Inc. Norcross, US). However,the results were flagged by the apparatus indicating somesort of discrepancy.

Grouping was then performed by tube technique using

217 Apollo Medicine, Vol. 7, No. 3, September 2010

TWO CASE REPORTS OF RARE WEAK ‘B’ SUBGROUP DETECTEDDURING ROUTINE TESTING

R N Makroo*, M Chowdhry**, A Bhatia***, R Gupta@, N L Rosamma# and J Phillip##

*Director, **Associate Consultant, ***Registrar, @DNB-Student, #Senior Technologist, ##Technologist,Department of Transfusion Medicine, Indraprastha Apollo Hospitals, Sarita Vihar, New Delhi 110 076, India.

Correspondence to: Dr RN Makroo, Director, Department of Transfusion Medicine, Immunology & Molecular Biology,Indraprastha Apollo Hospitals, Sarita Vihar, New Delhi 110 076, India.

E-mail: makroo@apollohospitals.com

Apart from the usual A, B, AB and O groups, there also exist many variant phenotypes. Variants of Type Bblood, with weak expression of the B antigen, have been previously described and are known to be rare. Theseusually require advanced techniques like ‘Adsorption and Elution’ for their detection. We present 2 similarcases of rare B subgroups identified at our department.

Key words: Weak B, Variant phenotypes, Adsorption, Elution.

Apollo Medicine, Vol. 7, No. 3, September 2010 218

Case Report

reagents provided by Tulip Diagnostics Pvt. Ltd.

The following reactions were noted at roomtemperature:

Forward grouping: O- Rh Positive

Reverse grouping: B

Reaction with anti H: 4+.

Blood grouping by tube technique was then performedat 4ºC and 37ºC to obtain the results as given in Table 1.

Since these results were inconclusive, furtherevaluation was done.

Cold adsorption and heat elution of the sample inquestion was performed with monoclonal as well aspolyclonal anti B sera in parallel. These tests are based onthe principle that red cells with weak expression of A or Bantigen may adsorb specific antibodies but do not showagglutination when tested with that antibody. Identifyingthe adsorbed antibody with after elution makes it possibleto demonstrate the presence of weak antigens [9].

Cold Adsorption

One ml of washed patient’s RBCs were mixed withone ml of anti B (monoclonal by Immucor Inc.) andincubated for one hour at 4ºC. The cells were then washedand last wash was preserved.

Heat Elution

Equal volumes of washed patient’s red cells and 6%bovine albumin were mixed in a tube and kept at 56º for 10minutes. The eluate was transferred into a fresh tube.

Both the test eluate and supernatant of last wash weretested for reverse grouping. The results were as shown inTable 2.

The results indicated the presence of anti B in theeluate, thereby demonstrating the presence of B antigen onthe surface of adsorbing (patient) cells.

The group was confirmed as weak subgroup of B.

Case 2

In a very similar case, a sample of a 28 year old lady,again coming for a master health check was received forABO & Rh grouping. The grouping was run on the fullyautomated platform: Galileo (Immucor Inc. Norcross US)that flagged the results. A similar discrepancy wasdetected between forward and reverse grouping, withforward group being O positive and reverse group being‘B’.

Grouping was repeated by tube technique followed bycold adsorption and heat elution as in case 1 to resolve thediscrepancy. The final ABO group in this case was alsoconfirmed to be weak subgroup of ‘B’.

To summarise, weak subgroups of ‘B’ are highlyuncommon and require advanced techniques like‘Adsorption and Elution’ for their detection. Moleculartesting is usually required for confirmation and exacttyping of the subgroups. However, for the purposes oftransfusion, such patients may be safely transfused with“O” group blood with corresponding Rh group.

REFERENCES

1. Watkins WM. Biochemistry and genetics of the ABO,Lewis, and P blood group systems. Adv Hum Genet1980; 10: 1.

2. Hearn VM, Smith ZG, Watkins WM. An a-N-acetylgalactosaminyl transferase associated with thehuman blood group A character. Biochem J 1968; 109:315.

3. Race C, Ziderman D, Watkins WM. An a-D-galactosyltransferase associated with the blood group Bcharacter. Biochem J 1968; 107: 733.

4. Yoshida A, Yamato K, Dave V, Yamaguchi H, and OkuboY. A Case of Weak Blood Group B Expression (Bm)

Table1

Temperature Anti A Anti B Anti AB Anti D A1 cell A2 cell B cell O cell

RT 0 0 0 4+ 4+ 4+ 0 0

4ºC 0 0 0 4+ 4+ 4+ 3+ 2+

37ºC 0 0 0 4+ 3+ 3+ 0 0

Table 2

Test Sample A cell B cell O cell

4ºC eluate 0 3+ 0

Last wash 0 0 0

Case Report

219 Apollo Medicine, Vol. 7, No. 3, September 2010

Associated with Abnormal Blood Group Galactosyl-transferase. Blood, 1982; 59 (2).

5. Race RR, Sanger R. Blood groups in man. 6th ed.Oxford: Blackwell Scientific Publications, 1975

6. Salmon C, Cartron JP, Rouger P. The human bloodgroups. New York: Masson Publishing, USA, 1984

7. Lopez M, Le Meud J, Gerbal A, Salmon C. Mesuresd’agglutination quantitative des phénotypes B faibles.Nouv Rev Franc Hémat 1973;13:107-118.

8. Geoff Daniels: Human Blood Groups. 2nd ed.

9. AABB Technical Manual. 15th ed.

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