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Blood Bank: Spring 2024 > ABO Blood Groups > Flashcards

ABO Blood Groups Flashcards

1
Q

Name and construct antigens on the RBC in the ABO system: A, B, and H antigens

A

See pic

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1
Q

Given phenotypic expression of ABO antigens, predict ABO blood types of offspring from various mating combos.

A

See pic

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2
Q

Forward typing

A

Use commercial anti-sera (Ab) against patients RBCs to detect blood group antigen

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3
Q

Reverse typing

A

Use patient sera against commercial RBCs (A1 and B cells) to see which Ab the patient produces

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4
Q

Word of the day

Bombay

A
  • Rare phenotype first described in Bombay, India where pt does not express A, B, or H antigen
  • These pt still have ABO genes that can be transferred to offspring but just can’t express them on RBC bc no H antigen to lock onto
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5
Q

Parabombay

A
  • These pt have no H Ag on RBCs but may express small amounts of A or B Ag on RBC surface bc FUT2 generates small amounts of secrete A or B Ag that can absorb onto RBC (type I chain)
  • Or caused by FUT1 that makes fucosyltransferase with very low activity
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6
Q

Type I substances

A

Secretions, can be absorbed onto RBCs, FUT2

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7
Q

Type II substances

A

Directly linked to RBC, FUT1

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8
Q

On which chromosome is the ABO gene found?

A

Chromosome 9

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9
Q

What does the ABO gene encode?

A

Encodes a glycosyltransferase that adds an N-terminal sugar to the end of H Ag attached to RBC

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10
Q

A transferase adds which sugar to H Ag?

A

N-acetyl-galactosamine (GalNAc)

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11
Q

B transferase adds which sugar to H Ag?

A

Galactose

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12
Q

If a stop codon is within the ABO gene, what does this imply?

A
  • No transferase is created, thus no sugar added to Type II substance
  • Patient is Type O
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13
Q

The H gene is found on which chromosome?

A

Chromosome 19

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14
Q

What does the H gene encode?

A

Fucosyltransferase that adds a fucose to outer-most sugar of a Type I or Type 2 precursor chain

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15
Q

T/F
The more H substance transferred to an A or B antigen, less detectible the H Ag

A

True

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16
Q

List the H Ag detectability in each blood type from greatest to lowest detectability

A

O > A2 > B > A2B > A1 > A1B

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17
Q

Why is H Ag not easily detectable in A1 or A1B patients?

A
  • Because almost all H Ag sites are converted to A1 or B, thus serologically masking H Ag
  • A1 and H have an inverse reciprocal relationship (more A1, less H)
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18
Q

T/F
Type 2 chain precursor can express A or B without conversion to H Ag

A

False
Must convert to H Ag before A or B can be expressed

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19
Q

T/F
As patients mature, Type 2 substance can become more branchy

A

True

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20
Q

Subgroup

A

When a pt may appear a weaker version of the blood type due to fewer branchy H Ag transferred to A or B

21
Q

What would cause a patient to form an antibody against anti-branchy H?

A

If only linear H Ag is transferred to A or B, then the branchy H may appear foreign if introduced through transfusion

22
Q

List the 2 most common A phenotypes

A
  • A1 = 80-90%
  • A2
23
Q

Describe the A1 phenotype

A
  • Branched A Ag (means that A attached to branched H Ag)
  • More A1/RBC than A2/RBC
  • Positive with anti-A Ab
  • Positive with anti-A1 lectin
  • Highly functioning A transferase transfers N-terminal sugar to branchy or linear H Ag no problem
  • Most common Ag expression of A
24
Q

Describe the A2 phenotype

A
  • Linear A antigens (means that A attached to linear H Ag)
  • Fewer A2/RBC than A1/RBC
  • Positive with anti-A Ab
  • Negative with anti-A1 lectin
  • Weaker A transferase only transfers N-terminal sugar to linear H Ag
  • Second most common expression of A
25
Q

anti-A1 lectin

A
  • Plant-derived compound with the purpose of distinguishing between A1 and A2 blood types
  • Positively reacts with A1 and negatively reacts with A2 bc it detects branchy substances
26
Q

T/F
B subgroups are more common than A subgroups

A

False
A subgroups (20% of time) are more common than B subgroups

27
Q

Which A subgroups weakly agglutinate with anti-A and/or anti-A,B?

A
  • A3
  • Aend
  • Ax
28
Q

Which A subgroups show no agglutination and must be detected by elution testing?

A
  • Am
  • Ay
  • Ael
29
Q

A3 subgroup

A
  • Mixed-field appearance (some parts agglutinate and some do not, appearing smoky)
  • 35k Ag
  • May make anti-A1 and secrete A Ag
30
Q

Aend subgroup

A
  • 10% RBCs hav enough A Ag to agglutinate serologically
  • About 3,500 Ag
31
Q

Ax subgroup

A
  • Does not agglutinate with anti-A
  • Does agglutinate with anti-A,B
  • 4k Ag
  • Almost always have anti-A1 in serum
32
Q

Am

A
  • Do not react strongly serologically
  • No anti-A1 in serum
  • Have detectable amounts of A enzyme in serum
  • 200-300 Ag
33
Q

Ay

A
  • Does not agglutinate serologically with anti-A
  • Does secrete A Ag in saliva
  • Recessive
  • No anti-A1
34
Q

Ael

A
  • Ag presence only detectible by adsorption/elution procedures
  • Have Ab that reacts with A1 and sometimes A2 cells
  • Only H substance in secretors and no A Ag in saliva
35
Q

B subgroup

A
  • Very efficient transferase activity
  • Strong serological activity
  • Detected by bandeirea simplicifolia lectin
  • 600k-800k Ag on RBC
36
Q

B3 subgroup

A
  • Mixed field agglutination with anti-B and anti-A,B
  • Weak transferase
  • Does not make anti-B
37
Q

Bx subgroup

A
  • Reacts weakly with anti-B and anti-A,B
  • NO detectible amounts of transferase
  • Makes weakly reactive anti-B Ab
38
Q

Bm subgroup

A
  • Detectible transferase but does not work well
  • Normal amount of B Ag on secretions
  • No anti-B detected (more freq in Japan)
39
Q

Bel subgroup

A
  • Must be detected by adsorption and elution studies
  • Weak anti-B may be present
  • B Ag not in secretions
40
Q

Why is there no B2 subgroup?

A

Bc no anti-B2 lectin exists to detect B attached to branchy H Ag

41
Q

Which lectin detects A1?

A

Dolichos biflorus

42
Q

Which lectin detects B?

A

Bandeiraea simplicifolia

43
Q

Which lectin detects H?

A

Ulex europaeus

44
Q

Describe Cis-AB anomaly

A
  • Rare splicing anomaly
  • A and B transferases are inherited on the same chromosome
  • Can pass AB blood type with O mate and can possibly produce type O children
45
Q

Describe B(A) pt anomaly

A
  • Mainly B antigen with some A present
  • Transferase prefers to transfer galactose but can also transfer GalNAc
  • Genetic variant of B gene
  • Polyclonal anti-sera
46
Q

Describe acquired B pt anomaly

A
  • If patient is originally A1 but has colon/rectal cancer, intestinal obstruction, gram-neg septicemia, then this can cause breakage of Ag to look like B Ag in a few RBCs
  • Mostly apparant with acified anti-sera
47
Q

Give example of acquired B anomaly

A

If pt is infected with E.coli, the bacteria have a deacetylating enzyme that removes the acetyl group from the A sugar, leaving a sugar that resembles D-galactose (appearance B)

48
Q

What does acquired B anomaly look like serologically?

A
  • anti-A: 4+
  • anti-B: 1+
  • anti-A, B: 4+
49
Q

Why is the ABO system important?

A
  • ABO system is the ONLY system where reciprocal (antithetical) Ab are consistent and predictable
  • Ab present in human plasma that have not been exposed to other human Ag (naturally occurring)

Blood Bank: Spring 2024 (10 decks)

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