Transfusion medicine

• Type: peptide
• M and N are present on glycophorin A protein, while S, s and U are present on glycophorin B protein
• Glycophorins A and B are encoded by 2 homologous genes, GYPA and GYPB, respectively, both of which are located on chromosome 4
• ~50 antigens in total (Fung: Technical Manual, 19th Edition, 2017)
• Glycophorin molecules contribute to RBC membrane structure with an association to band 3 and likewise act as ligands for Plasmodium falciparum (Fung: Technical Manual, 19th Edition, 2017)
• U is a high frequency antigen found on glycophorin B (Fung: Technical Manual, 19th Edition, 2017)
• Mur antigen is present in ~10% of Chinese and Thai individuals (Fung: Technical Manual, 19th Edition, 2017)

Race / ethnicity	M+N-	M+N+	M-N+	M-N-	S+s-	S+s+	S-s+	S-s-
White	30%	49%	21%	Rare	10%	42%	48%	Rare
Black (U.S.)	25%	49%	26%	Rare	6%	24%	68%	2%

• Adapted from Fung: Technical Manual, 19th Edition, 2017

• Antibodies to M and N are usually cold reactive, not clinically significant and naturally occurring, while S, s and U antibodies are clinically significant
• M antibodies tend to be IgM and are generally not associated with hemolytic disease of the fetus and newborn (HDFN) (rarely reported), though assessment for IgG conversion should be considered (AJP Rep 2017;7:e205)
• N antibodies are generally IgM
• S, s, U and other antibodies tend to be IgG and can cause hemolytic transfusion reactions and HDFN (Fung: Technical Manual, 19th Edition, 2017)
• N antigen exists on the N terminus of the glycophorin A peptide, similar to the N terminus of all glycophorin B peptides; hence antibodies against N are less common (Fung: Technical Manual, 19th Edition, 2017)
• Mur antibodies are common in Southeast Asia (Fung: Technical Manual, 19th Edition, 2017)

A gravida 1 para 0 mother is found to have an anti-M antibody. The clinical team wants to determine if the antibody is IgG or IgM. Treatment of the patient serum with which reagent destroys IgM antibodies and helps to determine if this is an IgG antibody?

1. Addition of antihuman globulin
2. Dithiothreitol (DTT)
3. Enzyme treatment
4. Polyethylene glycol (PEG) enhancement

B. Dithiothreitol (DTT)

Comment Here

Reference: MNSU system

A Jehovah's Witness patient agrees to receive plasma products only. A type and screen is found to be positive. The patient is disturbed when he sees this result in the patient portal, as he has no transfusion history. What is the best explanation to provide to the patient?

1. He has likely been transfused with RBCs at some point and this is evidence
2. These antibodies can be naturally occurring
3. This is likely passive transfer from his recent FFP transfusion
4. This patient needs a RBC transfusion

B. This could be a naturally occurring anti-M antibody

Comment Here

Reference: MNSU system