Your results may indicate a Bombay (Oh) phenotype dependant on the reactivity of the apparent Anti-H.  
 
The patient cells are apparently group O but negative with Anti-H - this is indicative of Bombay or para-Bombay.  
The expression of H antigen is inversely proportional to the expression of A and/or B antigen due to conversion of H substance to A or B. Hence group A1 people express very little H antigen and group O people express the most H antigen.  
 
You have detected an antibody that reacts against O cells and need to determine that it has anti-H specificity.  
Test the patients plasma against the following cells if possible:  
- cells from a known Bombay sample (H negative),  
- baby cord blood cells (H positive, I negative)  
- a panel of O cells of known phenotype for Rh, K, Fy, Jk, MNSs, P1 and Le.  
 
Anti-H in Bombay individuals is typically so strong that it still reacts at 37oC and by IAT - this is important in determining its clinical significance.  
 
Bombays are non-secretors - mostly Le(a+b-) but some Le(a-b-) - as secretion of A,B and H substance prevents the production of a potent Anti-H.  
 
Para Bombay is where very small amounts of H is produced and converted to A and/or B that can usually only be detected by absorption/elution techniques. The Anti-H is generally weaker and may not react at 37oC and in such cases would not be considered clinically significant.  
 
If the patient's antibody is an anti-H with thermal properties that indicates Bombay, the patient should be encouraged to donate blood to be frozen where such facilities exist or to at least regularly donate blood for others like them that are in need of H negative blood.  

Thanks a lot Dr Metz. I did ICT for this patient, it is positive. The patient is 6-7 months pregnant. She has one daughter, four years old. Her daughter's bloodgroup is O positive(cell are reactive with anti-H)  
Is there any risk of HDN to the fetus?

I think that if the mother was sensitised and produced immune anti-H in the previous Group O pregnancy, and the current foetus is also Group O, then HDN in this pregnancy is possible.

Thanks Dr Metz & Dr Hurwitz,  
Sorry for being late, but I have following comments on the issue;  
1)Bombay phenotype mother has Anti-H in her serum/plasma. So, I think, prior immunization by foetus O cells is not required. Can maternal Anti-H transmit through placenta? If yes, it can case HDN in group O foetus in any pregnancy, including first.  
2)Can we predict the severity of the reaction? ABO-HDN is usually mild because A & B antigens are not fully developed in the infant RBCs. What about H-antigen? Is it fully developed in the infant RBCs? Or Not?  
 
 
 
 

IgG antibody, but not IgM, can pass through the placenta. The ant-H found in subjects with Bombay blood group is usually IgM, but may be partly IgG. Thus, theoretically, the anti-H present in the maternal blood, if IgG, can cause immunisation and HDN, and this has been reported (Moores et al 1975. Transfusion 15;237-243).  
The H antigen on red cells of the newborn is not fully developed, and these cells react less strongly than those of adults. The number of H antigen sites is one-sixth that on adult cells.  
However, future pregnancies in your patient would have to be monitored closely.

Thank you Dr Metz for providing valuable information. This will definitely help me to understand the case.